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Instead, have a DataLayoutPass that holds one. This will allow parts of LLVM don't don't handle passes to also use DataLayout. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202168 91177308-0d34-0410-b5e6-96231b3b80d8
1192 lines
42 KiB
C++
1192 lines
42 KiB
C++
//===-- LoopReroll.cpp - Loop rerolling pass ------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass implements a simple loop reroller.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "loop-reroll"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/AliasSetTracker.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Analysis/ScalarEvolutionExpander.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetLibraryInfo.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/LoopUtils.h"
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using namespace llvm;
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STATISTIC(NumRerolledLoops, "Number of rerolled loops");
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static cl::opt<unsigned>
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MaxInc("max-reroll-increment", cl::init(2048), cl::Hidden,
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cl::desc("The maximum increment for loop rerolling"));
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// This loop re-rolling transformation aims to transform loops like this:
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//
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// int foo(int a);
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// void bar(int *x) {
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// for (int i = 0; i < 500; i += 3) {
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// foo(i);
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// foo(i+1);
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// foo(i+2);
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// }
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// }
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//
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// into a loop like this:
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//
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// void bar(int *x) {
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// for (int i = 0; i < 500; ++i)
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// foo(i);
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// }
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//
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// It does this by looking for loops that, besides the latch code, are composed
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// of isomorphic DAGs of instructions, with each DAG rooted at some increment
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// to the induction variable, and where each DAG is isomorphic to the DAG
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// rooted at the induction variable (excepting the sub-DAGs which root the
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// other induction-variable increments). In other words, we're looking for loop
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// bodies of the form:
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//
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// %iv = phi [ (preheader, ...), (body, %iv.next) ]
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// f(%iv)
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// %iv.1 = add %iv, 1 <-- a root increment
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// f(%iv.1)
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// %iv.2 = add %iv, 2 <-- a root increment
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// f(%iv.2)
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// %iv.scale_m_1 = add %iv, scale-1 <-- a root increment
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// f(%iv.scale_m_1)
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// ...
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// %iv.next = add %iv, scale
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// %cmp = icmp(%iv, ...)
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// br %cmp, header, exit
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//
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// where each f(i) is a set of instructions that, collectively, are a function
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// only of i (and other loop-invariant values).
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//
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// As a special case, we can also reroll loops like this:
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//
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// int foo(int);
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// void bar(int *x) {
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// for (int i = 0; i < 500; ++i) {
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// x[3*i] = foo(0);
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// x[3*i+1] = foo(0);
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// x[3*i+2] = foo(0);
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// }
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// }
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//
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// into this:
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//
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// void bar(int *x) {
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// for (int i = 0; i < 1500; ++i)
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// x[i] = foo(0);
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// }
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//
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// in which case, we're looking for inputs like this:
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//
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// %iv = phi [ (preheader, ...), (body, %iv.next) ]
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// %scaled.iv = mul %iv, scale
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// f(%scaled.iv)
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// %scaled.iv.1 = add %scaled.iv, 1
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// f(%scaled.iv.1)
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// %scaled.iv.2 = add %scaled.iv, 2
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// f(%scaled.iv.2)
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// %scaled.iv.scale_m_1 = add %scaled.iv, scale-1
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// f(%scaled.iv.scale_m_1)
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// ...
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// %iv.next = add %iv, 1
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// %cmp = icmp(%iv, ...)
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// br %cmp, header, exit
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namespace {
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class LoopReroll : public LoopPass {
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public:
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static char ID; // Pass ID, replacement for typeid
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LoopReroll() : LoopPass(ID) {
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initializeLoopRerollPass(*PassRegistry::getPassRegistry());
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}
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bool runOnLoop(Loop *L, LPPassManager &LPM);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<AliasAnalysis>();
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AU.addRequired<LoopInfo>();
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AU.addPreserved<LoopInfo>();
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AU.addRequired<DominatorTreeWrapperPass>();
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AU.addPreserved<DominatorTreeWrapperPass>();
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AU.addRequired<ScalarEvolution>();
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AU.addRequired<TargetLibraryInfo>();
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}
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protected:
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AliasAnalysis *AA;
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LoopInfo *LI;
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ScalarEvolution *SE;
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const DataLayout *DL;
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TargetLibraryInfo *TLI;
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DominatorTree *DT;
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typedef SmallVector<Instruction *, 16> SmallInstructionVector;
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typedef SmallSet<Instruction *, 16> SmallInstructionSet;
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// A chain of isomorphic instructions, indentified by a single-use PHI,
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// representing a reduction. Only the last value may be used outside the
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// loop.
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struct SimpleLoopReduction {
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SimpleLoopReduction(Instruction *P, Loop *L)
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: Valid(false), Instructions(1, P) {
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assert(isa<PHINode>(P) && "First reduction instruction must be a PHI");
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add(L);
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}
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bool valid() const {
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return Valid;
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}
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Instruction *getPHI() const {
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assert(Valid && "Using invalid reduction");
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return Instructions.front();
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}
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Instruction *getReducedValue() const {
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assert(Valid && "Using invalid reduction");
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return Instructions.back();
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}
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Instruction *get(size_t i) const {
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assert(Valid && "Using invalid reduction");
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return Instructions[i+1];
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}
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Instruction *operator [] (size_t i) const { return get(i); }
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// The size, ignoring the initial PHI.
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size_t size() const {
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assert(Valid && "Using invalid reduction");
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return Instructions.size()-1;
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}
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typedef SmallInstructionVector::iterator iterator;
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typedef SmallInstructionVector::const_iterator const_iterator;
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iterator begin() {
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assert(Valid && "Using invalid reduction");
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return llvm::next(Instructions.begin());
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}
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const_iterator begin() const {
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assert(Valid && "Using invalid reduction");
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return llvm::next(Instructions.begin());
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}
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iterator end() { return Instructions.end(); }
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const_iterator end() const { return Instructions.end(); }
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protected:
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bool Valid;
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SmallInstructionVector Instructions;
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void add(Loop *L);
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};
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// The set of all reductions, and state tracking of possible reductions
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// during loop instruction processing.
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struct ReductionTracker {
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typedef SmallVector<SimpleLoopReduction, 16> SmallReductionVector;
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// Add a new possible reduction.
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void addSLR(SimpleLoopReduction &SLR) {
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PossibleReds.push_back(SLR);
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}
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// Setup to track possible reductions corresponding to the provided
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// rerolling scale. Only reductions with a number of non-PHI instructions
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// that is divisible by the scale are considered. Three instructions sets
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// are filled in:
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// - A set of all possible instructions in eligible reductions.
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// - A set of all PHIs in eligible reductions
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// - A set of all reduced values (last instructions) in eligible reductions.
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void restrictToScale(uint64_t Scale,
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SmallInstructionSet &PossibleRedSet,
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SmallInstructionSet &PossibleRedPHISet,
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SmallInstructionSet &PossibleRedLastSet) {
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PossibleRedIdx.clear();
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PossibleRedIter.clear();
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Reds.clear();
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for (unsigned i = 0, e = PossibleReds.size(); i != e; ++i)
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if (PossibleReds[i].size() % Scale == 0) {
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PossibleRedLastSet.insert(PossibleReds[i].getReducedValue());
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PossibleRedPHISet.insert(PossibleReds[i].getPHI());
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PossibleRedSet.insert(PossibleReds[i].getPHI());
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PossibleRedIdx[PossibleReds[i].getPHI()] = i;
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for (SimpleLoopReduction::iterator J = PossibleReds[i].begin(),
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JE = PossibleReds[i].end(); J != JE; ++J) {
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PossibleRedSet.insert(*J);
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PossibleRedIdx[*J] = i;
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}
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}
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}
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// The functions below are used while processing the loop instructions.
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// Are the two instructions both from reductions, and furthermore, from
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// the same reduction?
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bool isPairInSame(Instruction *J1, Instruction *J2) {
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DenseMap<Instruction *, int>::iterator J1I = PossibleRedIdx.find(J1);
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if (J1I != PossibleRedIdx.end()) {
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DenseMap<Instruction *, int>::iterator J2I = PossibleRedIdx.find(J2);
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if (J2I != PossibleRedIdx.end() && J1I->second == J2I->second)
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return true;
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}
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return false;
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}
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// The two provided instructions, the first from the base iteration, and
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// the second from iteration i, form a matched pair. If these are part of
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// a reduction, record that fact.
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void recordPair(Instruction *J1, Instruction *J2, unsigned i) {
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if (PossibleRedIdx.count(J1)) {
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assert(PossibleRedIdx.count(J2) &&
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"Recording reduction vs. non-reduction instruction?");
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PossibleRedIter[J1] = 0;
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PossibleRedIter[J2] = i;
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int Idx = PossibleRedIdx[J1];
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assert(Idx == PossibleRedIdx[J2] &&
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"Recording pair from different reductions?");
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Reds.insert(Idx);
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}
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}
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// The functions below can be called after we've finished processing all
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// instructions in the loop, and we know which reductions were selected.
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// Is the provided instruction the PHI of a reduction selected for
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// rerolling?
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bool isSelectedPHI(Instruction *J) {
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if (!isa<PHINode>(J))
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return false;
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for (DenseSet<int>::iterator RI = Reds.begin(), RIE = Reds.end();
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RI != RIE; ++RI) {
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int i = *RI;
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if (cast<Instruction>(J) == PossibleReds[i].getPHI())
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return true;
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}
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return false;
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}
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bool validateSelected();
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void replaceSelected();
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protected:
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// The vector of all possible reductions (for any scale).
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SmallReductionVector PossibleReds;
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DenseMap<Instruction *, int> PossibleRedIdx;
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DenseMap<Instruction *, int> PossibleRedIter;
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DenseSet<int> Reds;
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};
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void collectPossibleIVs(Loop *L, SmallInstructionVector &PossibleIVs);
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void collectPossibleReductions(Loop *L,
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ReductionTracker &Reductions);
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void collectInLoopUserSet(Loop *L,
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const SmallInstructionVector &Roots,
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const SmallInstructionSet &Exclude,
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const SmallInstructionSet &Final,
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DenseSet<Instruction *> &Users);
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void collectInLoopUserSet(Loop *L,
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Instruction * Root,
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const SmallInstructionSet &Exclude,
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const SmallInstructionSet &Final,
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DenseSet<Instruction *> &Users);
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bool findScaleFromMul(Instruction *RealIV, uint64_t &Scale,
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Instruction *&IV,
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SmallInstructionVector &LoopIncs);
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bool collectAllRoots(Loop *L, uint64_t Inc, uint64_t Scale, Instruction *IV,
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SmallVector<SmallInstructionVector, 32> &Roots,
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SmallInstructionSet &AllRoots,
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SmallInstructionVector &LoopIncs);
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bool reroll(Instruction *IV, Loop *L, BasicBlock *Header, const SCEV *IterCount,
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ReductionTracker &Reductions);
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};
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}
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char LoopReroll::ID = 0;
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INITIALIZE_PASS_BEGIN(LoopReroll, "loop-reroll", "Reroll loops", false, false)
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INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
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INITIALIZE_PASS_DEPENDENCY(LoopInfo)
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
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INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
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INITIALIZE_PASS_END(LoopReroll, "loop-reroll", "Reroll loops", false, false)
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Pass *llvm::createLoopRerollPass() {
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return new LoopReroll;
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}
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// Returns true if the provided instruction is used outside the given loop.
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// This operates like Instruction::isUsedOutsideOfBlock, but considers PHIs in
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// non-loop blocks to be outside the loop.
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static bool hasUsesOutsideLoop(Instruction *I, Loop *L) {
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for (Value::use_iterator UI = I->use_begin(),
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UIE = I->use_end(); UI != UIE; ++UI) {
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Instruction *User = cast<Instruction>(*UI);
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if (!L->contains(User))
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return true;
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}
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return false;
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}
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// Collect the list of loop induction variables with respect to which it might
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// be possible to reroll the loop.
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void LoopReroll::collectPossibleIVs(Loop *L,
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SmallInstructionVector &PossibleIVs) {
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BasicBlock *Header = L->getHeader();
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for (BasicBlock::iterator I = Header->begin(),
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IE = Header->getFirstInsertionPt(); I != IE; ++I) {
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if (!isa<PHINode>(I))
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continue;
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if (!I->getType()->isIntegerTy())
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continue;
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if (const SCEVAddRecExpr *PHISCEV =
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dyn_cast<SCEVAddRecExpr>(SE->getSCEV(I))) {
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if (PHISCEV->getLoop() != L)
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continue;
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if (!PHISCEV->isAffine())
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continue;
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if (const SCEVConstant *IncSCEV =
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dyn_cast<SCEVConstant>(PHISCEV->getStepRecurrence(*SE))) {
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if (!IncSCEV->getValue()->getValue().isStrictlyPositive())
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continue;
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if (IncSCEV->getValue()->uge(MaxInc))
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continue;
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DEBUG(dbgs() << "LRR: Possible IV: " << *I << " = " <<
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*PHISCEV << "\n");
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PossibleIVs.push_back(I);
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}
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}
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}
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}
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// Add the remainder of the reduction-variable chain to the instruction vector
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// (the initial PHINode has already been added). If successful, the object is
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// marked as valid.
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void LoopReroll::SimpleLoopReduction::add(Loop *L) {
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assert(!Valid && "Cannot add to an already-valid chain");
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// The reduction variable must be a chain of single-use instructions
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// (including the PHI), except for the last value (which is used by the PHI
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// and also outside the loop).
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Instruction *C = Instructions.front();
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do {
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C = cast<Instruction>(*C->use_begin());
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if (C->hasOneUse()) {
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if (!C->isBinaryOp())
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return;
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if (!(isa<PHINode>(Instructions.back()) ||
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C->isSameOperationAs(Instructions.back())))
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return;
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Instructions.push_back(C);
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}
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} while (C->hasOneUse());
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if (Instructions.size() < 2 ||
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!C->isSameOperationAs(Instructions.back()) ||
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C->use_begin() == C->use_end())
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return;
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// C is now the (potential) last instruction in the reduction chain.
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for (Value::use_iterator UI = C->use_begin(), UIE = C->use_end();
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UI != UIE; ++UI) {
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// The only in-loop user can be the initial PHI.
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if (L->contains(cast<Instruction>(*UI)))
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if (cast<Instruction>(*UI ) != Instructions.front())
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return;
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}
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Instructions.push_back(C);
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Valid = true;
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}
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// Collect the vector of possible reduction variables.
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void LoopReroll::collectPossibleReductions(Loop *L,
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ReductionTracker &Reductions) {
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BasicBlock *Header = L->getHeader();
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for (BasicBlock::iterator I = Header->begin(),
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IE = Header->getFirstInsertionPt(); I != IE; ++I) {
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if (!isa<PHINode>(I))
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continue;
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if (!I->getType()->isSingleValueType())
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continue;
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SimpleLoopReduction SLR(I, L);
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if (!SLR.valid())
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continue;
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DEBUG(dbgs() << "LRR: Possible reduction: " << *I << " (with " <<
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SLR.size() << " chained instructions)\n");
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Reductions.addSLR(SLR);
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}
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}
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// Collect the set of all users of the provided root instruction. This set of
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// users contains not only the direct users of the root instruction, but also
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// all users of those users, and so on. There are two exceptions:
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//
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// 1. Instructions in the set of excluded instructions are never added to the
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// use set (even if they are users). This is used, for example, to exclude
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// including root increments in the use set of the primary IV.
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//
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// 2. Instructions in the set of final instructions are added to the use set
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// if they are users, but their users are not added. This is used, for
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// example, to prevent a reduction update from forcing all later reduction
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// updates into the use set.
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void LoopReroll::collectInLoopUserSet(Loop *L,
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Instruction *Root, const SmallInstructionSet &Exclude,
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const SmallInstructionSet &Final,
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DenseSet<Instruction *> &Users) {
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SmallInstructionVector Queue(1, Root);
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while (!Queue.empty()) {
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Instruction *I = Queue.pop_back_val();
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if (!Users.insert(I).second)
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continue;
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if (!Final.count(I))
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for (Value::use_iterator UI = I->use_begin(),
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UIE = I->use_end(); UI != UIE; ++UI) {
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Instruction *User = cast<Instruction>(*UI);
|
|
if (PHINode *PN = dyn_cast<PHINode>(User)) {
|
|
// Ignore "wrap-around" uses to PHIs of this loop's header.
|
|
if (PN->getIncomingBlock(UI) == L->getHeader())
|
|
continue;
|
|
}
|
|
|
|
if (L->contains(User) && !Exclude.count(User)) {
|
|
Queue.push_back(User);
|
|
}
|
|
}
|
|
|
|
// We also want to collect single-user "feeder" values.
|
|
for (User::op_iterator OI = I->op_begin(),
|
|
OIE = I->op_end(); OI != OIE; ++OI) {
|
|
if (Instruction *Op = dyn_cast<Instruction>(*OI))
|
|
if (Op->hasOneUse() && L->contains(Op) && !Exclude.count(Op) &&
|
|
!Final.count(Op))
|
|
Queue.push_back(Op);
|
|
}
|
|
}
|
|
}
|
|
|
|
// Collect all of the users of all of the provided root instructions (combined
|
|
// into a single set).
|
|
void LoopReroll::collectInLoopUserSet(Loop *L,
|
|
const SmallInstructionVector &Roots,
|
|
const SmallInstructionSet &Exclude,
|
|
const SmallInstructionSet &Final,
|
|
DenseSet<Instruction *> &Users) {
|
|
for (SmallInstructionVector::const_iterator I = Roots.begin(),
|
|
IE = Roots.end(); I != IE; ++I)
|
|
collectInLoopUserSet(L, *I, Exclude, Final, Users);
|
|
}
|
|
|
|
static bool isSimpleLoadStore(Instruction *I) {
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(I))
|
|
return LI->isSimple();
|
|
if (StoreInst *SI = dyn_cast<StoreInst>(I))
|
|
return SI->isSimple();
|
|
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I))
|
|
return !MI->isVolatile();
|
|
return false;
|
|
}
|
|
|
|
// Recognize loops that are setup like this:
|
|
//
|
|
// %iv = phi [ (preheader, ...), (body, %iv.next) ]
|
|
// %scaled.iv = mul %iv, scale
|
|
// f(%scaled.iv)
|
|
// %scaled.iv.1 = add %scaled.iv, 1
|
|
// f(%scaled.iv.1)
|
|
// %scaled.iv.2 = add %scaled.iv, 2
|
|
// f(%scaled.iv.2)
|
|
// %scaled.iv.scale_m_1 = add %scaled.iv, scale-1
|
|
// f(%scaled.iv.scale_m_1)
|
|
// ...
|
|
// %iv.next = add %iv, 1
|
|
// %cmp = icmp(%iv, ...)
|
|
// br %cmp, header, exit
|
|
//
|
|
// and, if found, set IV = %scaled.iv, and add %iv.next to LoopIncs.
|
|
bool LoopReroll::findScaleFromMul(Instruction *RealIV, uint64_t &Scale,
|
|
Instruction *&IV,
|
|
SmallInstructionVector &LoopIncs) {
|
|
// This is a special case: here we're looking for all uses (except for
|
|
// the increment) to be multiplied by a common factor. The increment must
|
|
// be by one. This is to capture loops like:
|
|
// for (int i = 0; i < 500; ++i) {
|
|
// foo(3*i); foo(3*i+1); foo(3*i+2);
|
|
// }
|
|
if (RealIV->getNumUses() != 2)
|
|
return false;
|
|
const SCEVAddRecExpr *RealIVSCEV = cast<SCEVAddRecExpr>(SE->getSCEV(RealIV));
|
|
Instruction *User1 = cast<Instruction>(*RealIV->use_begin()),
|
|
*User2 = cast<Instruction>(*llvm::next(RealIV->use_begin()));
|
|
if (!SE->isSCEVable(User1->getType()) || !SE->isSCEVable(User2->getType()))
|
|
return false;
|
|
const SCEVAddRecExpr *User1SCEV =
|
|
dyn_cast<SCEVAddRecExpr>(SE->getSCEV(User1)),
|
|
*User2SCEV =
|
|
dyn_cast<SCEVAddRecExpr>(SE->getSCEV(User2));
|
|
if (!User1SCEV || !User1SCEV->isAffine() ||
|
|
!User2SCEV || !User2SCEV->isAffine())
|
|
return false;
|
|
|
|
// We assume below that User1 is the scale multiply and User2 is the
|
|
// increment. If this can't be true, then swap them.
|
|
if (User1SCEV == RealIVSCEV->getPostIncExpr(*SE)) {
|
|
std::swap(User1, User2);
|
|
std::swap(User1SCEV, User2SCEV);
|
|
}
|
|
|
|
if (User2SCEV != RealIVSCEV->getPostIncExpr(*SE))
|
|
return false;
|
|
assert(User2SCEV->getStepRecurrence(*SE)->isOne() &&
|
|
"Invalid non-unit step for multiplicative scaling");
|
|
LoopIncs.push_back(User2);
|
|
|
|
if (const SCEVConstant *MulScale =
|
|
dyn_cast<SCEVConstant>(User1SCEV->getStepRecurrence(*SE))) {
|
|
// Make sure that both the start and step have the same multiplier.
|
|
if (RealIVSCEV->getStart()->getType() != MulScale->getType())
|
|
return false;
|
|
if (SE->getMulExpr(RealIVSCEV->getStart(), MulScale) !=
|
|
User1SCEV->getStart())
|
|
return false;
|
|
|
|
ConstantInt *MulScaleCI = MulScale->getValue();
|
|
if (!MulScaleCI->uge(2) || MulScaleCI->uge(MaxInc))
|
|
return false;
|
|
Scale = MulScaleCI->getZExtValue();
|
|
IV = User1;
|
|
} else
|
|
return false;
|
|
|
|
DEBUG(dbgs() << "LRR: Found possible scaling " << *User1 << "\n");
|
|
return true;
|
|
}
|
|
|
|
// Collect all root increments with respect to the provided induction variable
|
|
// (normally the PHI, but sometimes a multiply). A root increment is an
|
|
// instruction, normally an add, with a positive constant less than Scale. In a
|
|
// rerollable loop, each of these increments is the root of an instruction
|
|
// graph isomorphic to the others. Also, we collect the final induction
|
|
// increment (the increment equal to the Scale), and its users in LoopIncs.
|
|
bool LoopReroll::collectAllRoots(Loop *L, uint64_t Inc, uint64_t Scale,
|
|
Instruction *IV,
|
|
SmallVector<SmallInstructionVector, 32> &Roots,
|
|
SmallInstructionSet &AllRoots,
|
|
SmallInstructionVector &LoopIncs) {
|
|
for (Value::use_iterator UI = IV->use_begin(),
|
|
UIE = IV->use_end(); UI != UIE; ++UI) {
|
|
Instruction *User = cast<Instruction>(*UI);
|
|
if (!SE->isSCEVable(User->getType()))
|
|
continue;
|
|
if (User->getType() != IV->getType())
|
|
continue;
|
|
if (!L->contains(User))
|
|
continue;
|
|
if (hasUsesOutsideLoop(User, L))
|
|
continue;
|
|
|
|
if (const SCEVConstant *Diff = dyn_cast<SCEVConstant>(SE->getMinusSCEV(
|
|
SE->getSCEV(User), SE->getSCEV(IV)))) {
|
|
uint64_t Idx = Diff->getValue()->getValue().getZExtValue();
|
|
if (Idx > 0 && Idx < Scale) {
|
|
Roots[Idx-1].push_back(User);
|
|
AllRoots.insert(User);
|
|
} else if (Idx == Scale && Inc > 1) {
|
|
LoopIncs.push_back(User);
|
|
}
|
|
}
|
|
}
|
|
|
|
if (Roots[0].empty())
|
|
return false;
|
|
bool AllSame = true;
|
|
for (unsigned i = 1; i < Scale-1; ++i)
|
|
if (Roots[i].size() != Roots[0].size()) {
|
|
AllSame = false;
|
|
break;
|
|
}
|
|
|
|
if (!AllSame)
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
// Validate the selected reductions. All iterations must have an isomorphic
|
|
// part of the reduction chain and, for non-associative reductions, the chain
|
|
// entries must appear in order.
|
|
bool LoopReroll::ReductionTracker::validateSelected() {
|
|
// For a non-associative reduction, the chain entries must appear in order.
|
|
for (DenseSet<int>::iterator RI = Reds.begin(), RIE = Reds.end();
|
|
RI != RIE; ++RI) {
|
|
int i = *RI;
|
|
int PrevIter = 0, BaseCount = 0, Count = 0;
|
|
for (SimpleLoopReduction::iterator J = PossibleReds[i].begin(),
|
|
JE = PossibleReds[i].end(); J != JE; ++J) {
|
|
// Note that all instructions in the chain must have been found because
|
|
// all instructions in the function must have been assigned to some
|
|
// iteration.
|
|
int Iter = PossibleRedIter[*J];
|
|
if (Iter != PrevIter && Iter != PrevIter + 1 &&
|
|
!PossibleReds[i].getReducedValue()->isAssociative()) {
|
|
DEBUG(dbgs() << "LRR: Out-of-order non-associative reduction: " <<
|
|
*J << "\n");
|
|
return false;
|
|
}
|
|
|
|
if (Iter != PrevIter) {
|
|
if (Count != BaseCount) {
|
|
DEBUG(dbgs() << "LRR: Iteration " << PrevIter <<
|
|
" reduction use count " << Count <<
|
|
" is not equal to the base use count " <<
|
|
BaseCount << "\n");
|
|
return false;
|
|
}
|
|
|
|
Count = 0;
|
|
}
|
|
|
|
++Count;
|
|
if (Iter == 0)
|
|
++BaseCount;
|
|
|
|
PrevIter = Iter;
|
|
}
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
// For all selected reductions, remove all parts except those in the first
|
|
// iteration (and the PHI). Replace outside uses of the reduced value with uses
|
|
// of the first-iteration reduced value (in other words, reroll the selected
|
|
// reductions).
|
|
void LoopReroll::ReductionTracker::replaceSelected() {
|
|
// Fixup reductions to refer to the last instruction associated with the
|
|
// first iteration (not the last).
|
|
for (DenseSet<int>::iterator RI = Reds.begin(), RIE = Reds.end();
|
|
RI != RIE; ++RI) {
|
|
int i = *RI;
|
|
int j = 0;
|
|
for (int e = PossibleReds[i].size(); j != e; ++j)
|
|
if (PossibleRedIter[PossibleReds[i][j]] != 0) {
|
|
--j;
|
|
break;
|
|
}
|
|
|
|
// Replace users with the new end-of-chain value.
|
|
SmallInstructionVector Users;
|
|
for (Value::use_iterator UI =
|
|
PossibleReds[i].getReducedValue()->use_begin(),
|
|
UIE = PossibleReds[i].getReducedValue()->use_end(); UI != UIE; ++UI)
|
|
Users.push_back(cast<Instruction>(*UI));
|
|
|
|
for (SmallInstructionVector::iterator J = Users.begin(),
|
|
JE = Users.end(); J != JE; ++J)
|
|
(*J)->replaceUsesOfWith(PossibleReds[i].getReducedValue(),
|
|
PossibleReds[i][j]);
|
|
}
|
|
}
|
|
|
|
// Reroll the provided loop with respect to the provided induction variable.
|
|
// Generally, we're looking for a loop like this:
|
|
//
|
|
// %iv = phi [ (preheader, ...), (body, %iv.next) ]
|
|
// f(%iv)
|
|
// %iv.1 = add %iv, 1 <-- a root increment
|
|
// f(%iv.1)
|
|
// %iv.2 = add %iv, 2 <-- a root increment
|
|
// f(%iv.2)
|
|
// %iv.scale_m_1 = add %iv, scale-1 <-- a root increment
|
|
// f(%iv.scale_m_1)
|
|
// ...
|
|
// %iv.next = add %iv, scale
|
|
// %cmp = icmp(%iv, ...)
|
|
// br %cmp, header, exit
|
|
//
|
|
// Notably, we do not require that f(%iv), f(%iv.1), etc. be isolated groups of
|
|
// instructions. In other words, the instructions in f(%iv), f(%iv.1), etc. can
|
|
// be intermixed with eachother. The restriction imposed by this algorithm is
|
|
// that the relative order of the isomorphic instructions in f(%iv), f(%iv.1),
|
|
// etc. be the same.
|
|
//
|
|
// First, we collect the use set of %iv, excluding the other increment roots.
|
|
// This gives us f(%iv). Then we iterate over the loop instructions (scale-1)
|
|
// times, having collected the use set of f(%iv.(i+1)), during which we:
|
|
// - Ensure that the next unmatched instruction in f(%iv) is isomorphic to
|
|
// the next unmatched instruction in f(%iv.(i+1)).
|
|
// - Ensure that both matched instructions don't have any external users
|
|
// (with the exception of last-in-chain reduction instructions).
|
|
// - Track the (aliasing) write set, and other side effects, of all
|
|
// instructions that belong to future iterations that come before the matched
|
|
// instructions. If the matched instructions read from that write set, then
|
|
// f(%iv) or f(%iv.(i+1)) has some dependency on instructions in
|
|
// f(%iv.(j+1)) for some j > i, and we cannot reroll the loop. Similarly,
|
|
// if any of these future instructions had side effects (could not be
|
|
// speculatively executed), and so do the matched instructions, when we
|
|
// cannot reorder those side-effect-producing instructions, and rerolling
|
|
// fails.
|
|
//
|
|
// Finally, we make sure that all loop instructions are either loop increment
|
|
// roots, belong to simple latch code, parts of validated reductions, part of
|
|
// f(%iv) or part of some f(%iv.i). If all of that is true (and all reductions
|
|
// have been validated), then we reroll the loop.
|
|
bool LoopReroll::reroll(Instruction *IV, Loop *L, BasicBlock *Header,
|
|
const SCEV *IterCount,
|
|
ReductionTracker &Reductions) {
|
|
const SCEVAddRecExpr *RealIVSCEV = cast<SCEVAddRecExpr>(SE->getSCEV(IV));
|
|
uint64_t Inc = cast<SCEVConstant>(RealIVSCEV->getOperand(1))->
|
|
getValue()->getZExtValue();
|
|
// The collection of loop increment instructions.
|
|
SmallInstructionVector LoopIncs;
|
|
uint64_t Scale = Inc;
|
|
|
|
// The effective induction variable, IV, is normally also the real induction
|
|
// variable. When we're dealing with a loop like:
|
|
// for (int i = 0; i < 500; ++i)
|
|
// x[3*i] = ...;
|
|
// x[3*i+1] = ...;
|
|
// x[3*i+2] = ...;
|
|
// then the real IV is still i, but the effective IV is (3*i).
|
|
Instruction *RealIV = IV;
|
|
if (Inc == 1 && !findScaleFromMul(RealIV, Scale, IV, LoopIncs))
|
|
return false;
|
|
|
|
assert(Scale <= MaxInc && "Scale is too large");
|
|
assert(Scale > 1 && "Scale must be at least 2");
|
|
|
|
// The set of increment instructions for each increment value.
|
|
SmallVector<SmallInstructionVector, 32> Roots(Scale-1);
|
|
SmallInstructionSet AllRoots;
|
|
if (!collectAllRoots(L, Inc, Scale, IV, Roots, AllRoots, LoopIncs))
|
|
return false;
|
|
|
|
DEBUG(dbgs() << "LRR: Found all root induction increments for: " <<
|
|
*RealIV << "\n");
|
|
|
|
// An array of just the possible reductions for this scale factor. When we
|
|
// collect the set of all users of some root instructions, these reduction
|
|
// instructions are treated as 'final' (their uses are not considered).
|
|
// This is important because we don't want the root use set to search down
|
|
// the reduction chain.
|
|
SmallInstructionSet PossibleRedSet;
|
|
SmallInstructionSet PossibleRedLastSet, PossibleRedPHISet;
|
|
Reductions.restrictToScale(Scale, PossibleRedSet, PossibleRedPHISet,
|
|
PossibleRedLastSet);
|
|
|
|
// We now need to check for equivalence of the use graph of each root with
|
|
// that of the primary induction variable (excluding the roots). Our goal
|
|
// here is not to solve the full graph isomorphism problem, but rather to
|
|
// catch common cases without a lot of work. As a result, we will assume
|
|
// that the relative order of the instructions in each unrolled iteration
|
|
// is the same (although we will not make an assumption about how the
|
|
// different iterations are intermixed). Note that while the order must be
|
|
// the same, the instructions may not be in the same basic block.
|
|
SmallInstructionSet Exclude(AllRoots);
|
|
Exclude.insert(LoopIncs.begin(), LoopIncs.end());
|
|
|
|
DenseSet<Instruction *> BaseUseSet;
|
|
collectInLoopUserSet(L, IV, Exclude, PossibleRedSet, BaseUseSet);
|
|
|
|
DenseSet<Instruction *> AllRootUses;
|
|
std::vector<DenseSet<Instruction *> > RootUseSets(Scale-1);
|
|
|
|
bool MatchFailed = false;
|
|
for (unsigned i = 0; i < Scale-1 && !MatchFailed; ++i) {
|
|
DenseSet<Instruction *> &RootUseSet = RootUseSets[i];
|
|
collectInLoopUserSet(L, Roots[i], SmallInstructionSet(),
|
|
PossibleRedSet, RootUseSet);
|
|
|
|
DEBUG(dbgs() << "LRR: base use set size: " << BaseUseSet.size() <<
|
|
" vs. iteration increment " << (i+1) <<
|
|
" use set size: " << RootUseSet.size() << "\n");
|
|
|
|
if (BaseUseSet.size() != RootUseSet.size()) {
|
|
MatchFailed = true;
|
|
break;
|
|
}
|
|
|
|
// In addition to regular aliasing information, we need to look for
|
|
// instructions from later (future) iterations that have side effects
|
|
// preventing us from reordering them past other instructions with side
|
|
// effects.
|
|
bool FutureSideEffects = false;
|
|
AliasSetTracker AST(*AA);
|
|
|
|
// The map between instructions in f(%iv.(i+1)) and f(%iv).
|
|
DenseMap<Value *, Value *> BaseMap;
|
|
|
|
assert(L->getNumBlocks() == 1 && "Cannot handle multi-block loops");
|
|
for (BasicBlock::iterator J1 = Header->begin(), J2 = Header->begin(),
|
|
JE = Header->end(); J1 != JE && !MatchFailed; ++J1) {
|
|
if (cast<Instruction>(J1) == RealIV)
|
|
continue;
|
|
if (cast<Instruction>(J1) == IV)
|
|
continue;
|
|
if (!BaseUseSet.count(J1))
|
|
continue;
|
|
if (PossibleRedPHISet.count(J1)) // Skip reduction PHIs.
|
|
continue;
|
|
|
|
while (J2 != JE && (!RootUseSet.count(J2) ||
|
|
std::find(Roots[i].begin(), Roots[i].end(), J2) !=
|
|
Roots[i].end())) {
|
|
// As we iterate through the instructions, instructions that don't
|
|
// belong to previous iterations (or the base case), must belong to
|
|
// future iterations. We want to track the alias set of writes from
|
|
// previous iterations.
|
|
if (!isa<PHINode>(J2) && !BaseUseSet.count(J2) &&
|
|
!AllRootUses.count(J2)) {
|
|
if (J2->mayWriteToMemory())
|
|
AST.add(J2);
|
|
|
|
// Note: This is specifically guarded by a check on isa<PHINode>,
|
|
// which while a valid (somewhat arbitrary) micro-optimization, is
|
|
// needed because otherwise isSafeToSpeculativelyExecute returns
|
|
// false on PHI nodes.
|
|
if (!isSimpleLoadStore(J2) && !isSafeToSpeculativelyExecute(J2, DL))
|
|
FutureSideEffects = true;
|
|
}
|
|
|
|
++J2;
|
|
}
|
|
|
|
if (!J1->isSameOperationAs(J2)) {
|
|
DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
|
|
" vs. " << *J2 << "\n");
|
|
MatchFailed = true;
|
|
break;
|
|
}
|
|
|
|
// Make sure that this instruction, which is in the use set of this
|
|
// root instruction, does not also belong to the base set or the set of
|
|
// some previous root instruction.
|
|
if (BaseUseSet.count(J2) || AllRootUses.count(J2)) {
|
|
DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
|
|
" vs. " << *J2 << " (prev. case overlap)\n");
|
|
MatchFailed = true;
|
|
break;
|
|
}
|
|
|
|
// Make sure that we don't alias with any instruction in the alias set
|
|
// tracker. If we do, then we depend on a future iteration, and we
|
|
// can't reroll.
|
|
if (J2->mayReadFromMemory()) {
|
|
for (AliasSetTracker::iterator K = AST.begin(), KE = AST.end();
|
|
K != KE && !MatchFailed; ++K) {
|
|
if (K->aliasesUnknownInst(J2, *AA)) {
|
|
DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
|
|
" vs. " << *J2 << " (depends on future store)\n");
|
|
MatchFailed = true;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
// If we've past an instruction from a future iteration that may have
|
|
// side effects, and this instruction might also, then we can't reorder
|
|
// them, and this matching fails. As an exception, we allow the alias
|
|
// set tracker to handle regular (simple) load/store dependencies.
|
|
if (FutureSideEffects &&
|
|
((!isSimpleLoadStore(J1) && !isSafeToSpeculativelyExecute(J1)) ||
|
|
(!isSimpleLoadStore(J2) && !isSafeToSpeculativelyExecute(J2)))) {
|
|
DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
|
|
" vs. " << *J2 <<
|
|
" (side effects prevent reordering)\n");
|
|
MatchFailed = true;
|
|
break;
|
|
}
|
|
|
|
// For instructions that are part of a reduction, if the operation is
|
|
// associative, then don't bother matching the operands (because we
|
|
// already know that the instructions are isomorphic, and the order
|
|
// within the iteration does not matter). For non-associative reductions,
|
|
// we do need to match the operands, because we need to reject
|
|
// out-of-order instructions within an iteration!
|
|
// For example (assume floating-point addition), we need to reject this:
|
|
// x += a[i]; x += b[i];
|
|
// x += a[i+1]; x += b[i+1];
|
|
// x += b[i+2]; x += a[i+2];
|
|
bool InReduction = Reductions.isPairInSame(J1, J2);
|
|
|
|
if (!(InReduction && J1->isAssociative())) {
|
|
bool Swapped = false, SomeOpMatched = false;;
|
|
for (unsigned j = 0; j < J1->getNumOperands() && !MatchFailed; ++j) {
|
|
Value *Op2 = J2->getOperand(j);
|
|
|
|
// If this is part of a reduction (and the operation is not
|
|
// associatve), then we match all operands, but not those that are
|
|
// part of the reduction.
|
|
if (InReduction)
|
|
if (Instruction *Op2I = dyn_cast<Instruction>(Op2))
|
|
if (Reductions.isPairInSame(J2, Op2I))
|
|
continue;
|
|
|
|
DenseMap<Value *, Value *>::iterator BMI = BaseMap.find(Op2);
|
|
if (BMI != BaseMap.end())
|
|
Op2 = BMI->second;
|
|
else if (std::find(Roots[i].begin(), Roots[i].end(),
|
|
(Instruction*) Op2) != Roots[i].end())
|
|
Op2 = IV;
|
|
|
|
if (J1->getOperand(Swapped ? unsigned(!j) : j) != Op2) {
|
|
// If we've not already decided to swap the matched operands, and
|
|
// we've not already matched our first operand (note that we could
|
|
// have skipped matching the first operand because it is part of a
|
|
// reduction above), and the instruction is commutative, then try
|
|
// the swapped match.
|
|
if (!Swapped && J1->isCommutative() && !SomeOpMatched &&
|
|
J1->getOperand(!j) == Op2) {
|
|
Swapped = true;
|
|
} else {
|
|
DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
|
|
" vs. " << *J2 << " (operand " << j << ")\n");
|
|
MatchFailed = true;
|
|
break;
|
|
}
|
|
}
|
|
|
|
SomeOpMatched = true;
|
|
}
|
|
}
|
|
|
|
if ((!PossibleRedLastSet.count(J1) && hasUsesOutsideLoop(J1, L)) ||
|
|
(!PossibleRedLastSet.count(J2) && hasUsesOutsideLoop(J2, L))) {
|
|
DEBUG(dbgs() << "LRR: iteration root match failed at " << *J1 <<
|
|
" vs. " << *J2 << " (uses outside loop)\n");
|
|
MatchFailed = true;
|
|
break;
|
|
}
|
|
|
|
if (!MatchFailed)
|
|
BaseMap.insert(std::pair<Value *, Value *>(J2, J1));
|
|
|
|
AllRootUses.insert(J2);
|
|
Reductions.recordPair(J1, J2, i+1);
|
|
|
|
++J2;
|
|
}
|
|
}
|
|
|
|
if (MatchFailed)
|
|
return false;
|
|
|
|
DEBUG(dbgs() << "LRR: Matched all iteration increments for " <<
|
|
*RealIV << "\n");
|
|
|
|
DenseSet<Instruction *> LoopIncUseSet;
|
|
collectInLoopUserSet(L, LoopIncs, SmallInstructionSet(),
|
|
SmallInstructionSet(), LoopIncUseSet);
|
|
DEBUG(dbgs() << "LRR: Loop increment set size: " <<
|
|
LoopIncUseSet.size() << "\n");
|
|
|
|
// Make sure that all instructions in the loop have been included in some
|
|
// use set.
|
|
for (BasicBlock::iterator J = Header->begin(), JE = Header->end();
|
|
J != JE; ++J) {
|
|
if (isa<DbgInfoIntrinsic>(J))
|
|
continue;
|
|
if (cast<Instruction>(J) == RealIV)
|
|
continue;
|
|
if (cast<Instruction>(J) == IV)
|
|
continue;
|
|
if (BaseUseSet.count(J) || AllRootUses.count(J) ||
|
|
(LoopIncUseSet.count(J) && (J->isTerminator() ||
|
|
isSafeToSpeculativelyExecute(J, DL))))
|
|
continue;
|
|
|
|
if (AllRoots.count(J))
|
|
continue;
|
|
|
|
if (Reductions.isSelectedPHI(J))
|
|
continue;
|
|
|
|
DEBUG(dbgs() << "LRR: aborting reroll based on " << *RealIV <<
|
|
" unprocessed instruction found: " << *J << "\n");
|
|
MatchFailed = true;
|
|
break;
|
|
}
|
|
|
|
if (MatchFailed)
|
|
return false;
|
|
|
|
DEBUG(dbgs() << "LRR: all instructions processed from " <<
|
|
*RealIV << "\n");
|
|
|
|
if (!Reductions.validateSelected())
|
|
return false;
|
|
|
|
// At this point, we've validated the rerolling, and we're committed to
|
|
// making changes!
|
|
|
|
Reductions.replaceSelected();
|
|
|
|
// Remove instructions associated with non-base iterations.
|
|
for (BasicBlock::reverse_iterator J = Header->rbegin();
|
|
J != Header->rend();) {
|
|
if (AllRootUses.count(&*J)) {
|
|
Instruction *D = &*J;
|
|
DEBUG(dbgs() << "LRR: removing: " << *D << "\n");
|
|
D->eraseFromParent();
|
|
continue;
|
|
}
|
|
|
|
++J;
|
|
}
|
|
|
|
// Insert the new induction variable.
|
|
const SCEV *Start = RealIVSCEV->getStart();
|
|
if (Inc == 1)
|
|
Start = SE->getMulExpr(Start,
|
|
SE->getConstant(Start->getType(), Scale));
|
|
const SCEVAddRecExpr *H =
|
|
cast<SCEVAddRecExpr>(SE->getAddRecExpr(Start,
|
|
SE->getConstant(RealIVSCEV->getType(), 1),
|
|
L, SCEV::FlagAnyWrap));
|
|
{ // Limit the lifetime of SCEVExpander.
|
|
SCEVExpander Expander(*SE, "reroll");
|
|
Value *NewIV = Expander.expandCodeFor(H, IV->getType(), Header->begin());
|
|
|
|
for (DenseSet<Instruction *>::iterator J = BaseUseSet.begin(),
|
|
JE = BaseUseSet.end(); J != JE; ++J)
|
|
(*J)->replaceUsesOfWith(IV, NewIV);
|
|
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(Header->getTerminator())) {
|
|
if (LoopIncUseSet.count(BI)) {
|
|
const SCEV *ICSCEV = RealIVSCEV->evaluateAtIteration(IterCount, *SE);
|
|
if (Inc == 1)
|
|
ICSCEV =
|
|
SE->getMulExpr(ICSCEV, SE->getConstant(ICSCEV->getType(), Scale));
|
|
// Iteration count SCEV minus 1
|
|
const SCEV *ICMinus1SCEV =
|
|
SE->getMinusSCEV(ICSCEV, SE->getConstant(ICSCEV->getType(), 1));
|
|
|
|
Value *ICMinus1; // Iteration count minus 1
|
|
if (isa<SCEVConstant>(ICMinus1SCEV)) {
|
|
ICMinus1 = Expander.expandCodeFor(ICMinus1SCEV, NewIV->getType(), BI);
|
|
} else {
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
if (!Preheader)
|
|
Preheader = InsertPreheaderForLoop(L, this);
|
|
|
|
ICMinus1 = Expander.expandCodeFor(ICMinus1SCEV, NewIV->getType(),
|
|
Preheader->getTerminator());
|
|
}
|
|
|
|
Value *Cond = new ICmpInst(BI, CmpInst::ICMP_EQ, NewIV, ICMinus1,
|
|
"exitcond");
|
|
BI->setCondition(Cond);
|
|
|
|
if (BI->getSuccessor(1) != Header)
|
|
BI->swapSuccessors();
|
|
}
|
|
}
|
|
}
|
|
|
|
SimplifyInstructionsInBlock(Header, DL, TLI);
|
|
DeleteDeadPHIs(Header, TLI);
|
|
++NumRerolledLoops;
|
|
return true;
|
|
}
|
|
|
|
bool LoopReroll::runOnLoop(Loop *L, LPPassManager &LPM) {
|
|
if (skipOptnoneFunction(L))
|
|
return false;
|
|
|
|
AA = &getAnalysis<AliasAnalysis>();
|
|
LI = &getAnalysis<LoopInfo>();
|
|
SE = &getAnalysis<ScalarEvolution>();
|
|
TLI = &getAnalysis<TargetLibraryInfo>();
|
|
DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
|
|
DL = DLP ? &DLP->getDataLayout() : 0;
|
|
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
|
|
|
|
BasicBlock *Header = L->getHeader();
|
|
DEBUG(dbgs() << "LRR: F[" << Header->getParent()->getName() <<
|
|
"] Loop %" << Header->getName() << " (" <<
|
|
L->getNumBlocks() << " block(s))\n");
|
|
|
|
bool Changed = false;
|
|
|
|
// For now, we'll handle only single BB loops.
|
|
if (L->getNumBlocks() > 1)
|
|
return Changed;
|
|
|
|
if (!SE->hasLoopInvariantBackedgeTakenCount(L))
|
|
return Changed;
|
|
|
|
const SCEV *LIBETC = SE->getBackedgeTakenCount(L);
|
|
const SCEV *IterCount =
|
|
SE->getAddExpr(LIBETC, SE->getConstant(LIBETC->getType(), 1));
|
|
DEBUG(dbgs() << "LRR: iteration count = " << *IterCount << "\n");
|
|
|
|
// First, we need to find the induction variable with respect to which we can
|
|
// reroll (there may be several possible options).
|
|
SmallInstructionVector PossibleIVs;
|
|
collectPossibleIVs(L, PossibleIVs);
|
|
|
|
if (PossibleIVs.empty()) {
|
|
DEBUG(dbgs() << "LRR: No possible IVs found\n");
|
|
return Changed;
|
|
}
|
|
|
|
ReductionTracker Reductions;
|
|
collectPossibleReductions(L, Reductions);
|
|
|
|
// For each possible IV, collect the associated possible set of 'root' nodes
|
|
// (i+1, i+2, etc.).
|
|
for (SmallInstructionVector::iterator I = PossibleIVs.begin(),
|
|
IE = PossibleIVs.end(); I != IE; ++I)
|
|
if (reroll(*I, L, Header, IterCount, Reductions)) {
|
|
Changed = true;
|
|
break;
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|