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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72132 91177308-0d34-0410-b5e6-96231b3b80d8
865 lines
34 KiB
C++
865 lines
34 KiB
C++
//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
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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 transformation analyzes and transforms the induction variables (and
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// computations derived from them) into simpler forms suitable for subsequent
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// analysis and transformation.
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//
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// This transformation makes the following changes to each loop with an
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// identifiable induction variable:
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// 1. All loops are transformed to have a SINGLE canonical induction variable
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// which starts at zero and steps by one.
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// 2. The canonical induction variable is guaranteed to be the first PHI node
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// in the loop header block.
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// 3. Any pointer arithmetic recurrences are raised to use array subscripts.
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//
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// If the trip count of a loop is computable, this pass also makes the following
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// changes:
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// 1. The exit condition for the loop is canonicalized to compare the
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// induction value against the exit value. This turns loops like:
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// 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)'
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// 2. Any use outside of the loop of an expression derived from the indvar
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// is changed to compute the derived value outside of the loop, eliminating
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// the dependence on the exit value of the induction variable. If the only
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// purpose of the loop is to compute the exit value of some derived
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// expression, this transformation will make the loop dead.
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//
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// This transformation should be followed by strength reduction after all of the
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// desired loop transformations have been performed.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "indvars"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/Type.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/IVUsers.h"
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#include "llvm/Analysis/ScalarEvolutionExpander.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/STLExtras.h"
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using namespace llvm;
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STATISTIC(NumRemoved , "Number of aux indvars removed");
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STATISTIC(NumInserted, "Number of canonical indvars added");
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STATISTIC(NumReplaced, "Number of exit values replaced");
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STATISTIC(NumLFTR , "Number of loop exit tests replaced");
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namespace {
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class VISIBILITY_HIDDEN IndVarSimplify : public LoopPass {
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IVUsers *IU;
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LoopInfo *LI;
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ScalarEvolution *SE;
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bool Changed;
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public:
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static char ID; // Pass identification, replacement for typeid
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IndVarSimplify() : LoopPass(&ID) {}
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virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<DominatorTree>();
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AU.addRequired<ScalarEvolution>();
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AU.addRequiredID(LCSSAID);
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AU.addRequiredID(LoopSimplifyID);
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AU.addRequired<LoopInfo>();
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AU.addRequired<IVUsers>();
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AU.addPreserved<ScalarEvolution>();
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AU.addPreservedID(LoopSimplifyID);
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AU.addPreserved<IVUsers>();
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AU.addPreservedID(LCSSAID);
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AU.setPreservesCFG();
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}
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private:
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void RewriteNonIntegerIVs(Loop *L);
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ICmpInst *LinearFunctionTestReplace(Loop *L, SCEVHandle BackedgeTakenCount,
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Value *IndVar,
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BasicBlock *ExitingBlock,
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BranchInst *BI,
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SCEVExpander &Rewriter);
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void RewriteLoopExitValues(Loop *L, const SCEV *BackedgeTakenCount);
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void RewriteIVExpressions(Loop *L, const Type *LargestType,
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SCEVExpander &Rewriter);
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void SinkUnusedInvariants(Loop *L, SCEVExpander &Rewriter);
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void FixUsesBeforeDefs(Loop *L, SCEVExpander &Rewriter);
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void HandleFloatingPointIV(Loop *L, PHINode *PH);
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};
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}
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char IndVarSimplify::ID = 0;
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static RegisterPass<IndVarSimplify>
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X("indvars", "Canonicalize Induction Variables");
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Pass *llvm::createIndVarSimplifyPass() {
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return new IndVarSimplify();
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}
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/// LinearFunctionTestReplace - This method rewrites the exit condition of the
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/// loop to be a canonical != comparison against the incremented loop induction
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/// variable. This pass is able to rewrite the exit tests of any loop where the
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/// SCEV analysis can determine a loop-invariant trip count of the loop, which
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/// is actually a much broader range than just linear tests.
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ICmpInst *IndVarSimplify::LinearFunctionTestReplace(Loop *L,
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SCEVHandle BackedgeTakenCount,
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Value *IndVar,
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BasicBlock *ExitingBlock,
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BranchInst *BI,
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SCEVExpander &Rewriter) {
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// If the exiting block is not the same as the backedge block, we must compare
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// against the preincremented value, otherwise we prefer to compare against
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// the post-incremented value.
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Value *CmpIndVar;
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SCEVHandle RHS = BackedgeTakenCount;
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if (ExitingBlock == L->getLoopLatch()) {
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// Add one to the "backedge-taken" count to get the trip count.
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// If this addition may overflow, we have to be more pessimistic and
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// cast the induction variable before doing the add.
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SCEVHandle Zero = SE->getIntegerSCEV(0, BackedgeTakenCount->getType());
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SCEVHandle N =
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SE->getAddExpr(BackedgeTakenCount,
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SE->getIntegerSCEV(1, BackedgeTakenCount->getType()));
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if ((isa<SCEVConstant>(N) && !N->isZero()) ||
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SE->isLoopGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
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// No overflow. Cast the sum.
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RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType());
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} else {
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// Potential overflow. Cast before doing the add.
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RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
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IndVar->getType());
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RHS = SE->getAddExpr(RHS,
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SE->getIntegerSCEV(1, IndVar->getType()));
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}
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// The BackedgeTaken expression contains the number of times that the
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// backedge branches to the loop header. This is one less than the
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// number of times the loop executes, so use the incremented indvar.
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CmpIndVar = L->getCanonicalInductionVariableIncrement();
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} else {
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// We have to use the preincremented value...
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RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
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IndVar->getType());
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CmpIndVar = IndVar;
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}
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// Expand the code for the iteration count into the preheader of the loop.
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BasicBlock *Preheader = L->getLoopPreheader();
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Value *ExitCnt = Rewriter.expandCodeFor(RHS, CmpIndVar->getType(),
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Preheader->getTerminator());
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// Insert a new icmp_ne or icmp_eq instruction before the branch.
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ICmpInst::Predicate Opcode;
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if (L->contains(BI->getSuccessor(0)))
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Opcode = ICmpInst::ICMP_NE;
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else
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Opcode = ICmpInst::ICMP_EQ;
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DOUT << "INDVARS: Rewriting loop exit condition to:\n"
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<< " LHS:" << *CmpIndVar // includes a newline
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<< " op:\t"
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<< (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
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<< " RHS:\t" << *RHS << "\n";
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ICmpInst *Cond = new ICmpInst(Opcode, CmpIndVar, ExitCnt, "exitcond", BI);
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Instruction *OrigCond = cast<Instruction>(BI->getCondition());
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OrigCond->replaceAllUsesWith(Cond);
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RecursivelyDeleteTriviallyDeadInstructions(OrigCond);
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++NumLFTR;
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Changed = true;
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return Cond;
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}
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/// RewriteLoopExitValues - Check to see if this loop has a computable
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/// loop-invariant execution count. If so, this means that we can compute the
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/// final value of any expressions that are recurrent in the loop, and
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/// substitute the exit values from the loop into any instructions outside of
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/// the loop that use the final values of the current expressions.
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///
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/// This is mostly redundant with the regular IndVarSimplify activities that
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/// happen later, except that it's more powerful in some cases, because it's
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/// able to brute-force evaluate arbitrary instructions as long as they have
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/// constant operands at the beginning of the loop.
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void IndVarSimplify::RewriteLoopExitValues(Loop *L,
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const SCEV *BackedgeTakenCount) {
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// Verify the input to the pass in already in LCSSA form.
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assert(L->isLCSSAForm());
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BasicBlock *Preheader = L->getLoopPreheader();
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// Scan all of the instructions in the loop, looking at those that have
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// extra-loop users and which are recurrences.
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SCEVExpander Rewriter(*SE);
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// We insert the code into the preheader of the loop if the loop contains
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// multiple exit blocks, or in the exit block if there is exactly one.
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BasicBlock *BlockToInsertInto;
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SmallVector<BasicBlock*, 8> ExitBlocks;
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L->getUniqueExitBlocks(ExitBlocks);
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if (ExitBlocks.size() == 1)
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BlockToInsertInto = ExitBlocks[0];
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else
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BlockToInsertInto = Preheader;
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BasicBlock::iterator InsertPt = BlockToInsertInto->getFirstNonPHI();
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std::map<Instruction*, Value*> ExitValues;
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// Find all values that are computed inside the loop, but used outside of it.
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// Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan
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// the exit blocks of the loop to find them.
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for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
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BasicBlock *ExitBB = ExitBlocks[i];
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// If there are no PHI nodes in this exit block, then no values defined
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// inside the loop are used on this path, skip it.
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PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
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if (!PN) continue;
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unsigned NumPreds = PN->getNumIncomingValues();
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// Iterate over all of the PHI nodes.
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BasicBlock::iterator BBI = ExitBB->begin();
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while ((PN = dyn_cast<PHINode>(BBI++))) {
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// Iterate over all of the values in all the PHI nodes.
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for (unsigned i = 0; i != NumPreds; ++i) {
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// If the value being merged in is not integer or is not defined
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// in the loop, skip it.
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Value *InVal = PN->getIncomingValue(i);
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if (!isa<Instruction>(InVal) ||
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// SCEV only supports integer expressions for now.
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(!isa<IntegerType>(InVal->getType()) &&
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!isa<PointerType>(InVal->getType())))
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continue;
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// If this pred is for a subloop, not L itself, skip it.
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if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
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continue; // The Block is in a subloop, skip it.
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// Check that InVal is defined in the loop.
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Instruction *Inst = cast<Instruction>(InVal);
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if (!L->contains(Inst->getParent()))
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continue;
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// Okay, this instruction has a user outside of the current loop
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// and varies predictably *inside* the loop. Evaluate the value it
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// contains when the loop exits, if possible.
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SCEVHandle SH = SE->getSCEV(Inst);
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SCEVHandle ExitValue = SE->getSCEVAtScope(SH, L->getParentLoop());
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if (isa<SCEVCouldNotCompute>(ExitValue) ||
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!ExitValue->isLoopInvariant(L))
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continue;
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Changed = true;
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++NumReplaced;
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// See if we already computed the exit value for the instruction, if so,
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// just reuse it.
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Value *&ExitVal = ExitValues[Inst];
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if (!ExitVal)
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ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), InsertPt);
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DOUT << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal
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<< " LoopVal = " << *Inst << "\n";
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PN->setIncomingValue(i, ExitVal);
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// If this instruction is dead now, delete it.
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RecursivelyDeleteTriviallyDeadInstructions(Inst);
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// See if this is a single-entry LCSSA PHI node. If so, we can (and
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// have to) remove
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// the PHI entirely. This is safe, because the NewVal won't be variant
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// in the loop, so we don't need an LCSSA phi node anymore.
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if (NumPreds == 1) {
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PN->replaceAllUsesWith(ExitVal);
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RecursivelyDeleteTriviallyDeadInstructions(PN);
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break;
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}
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}
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}
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}
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}
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void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) {
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// First step. Check to see if there are any floating-point recurrences.
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// If there are, change them into integer recurrences, permitting analysis by
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// the SCEV routines.
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//
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BasicBlock *Header = L->getHeader();
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SmallVector<WeakVH, 8> PHIs;
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for (BasicBlock::iterator I = Header->begin();
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PHINode *PN = dyn_cast<PHINode>(I); ++I)
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PHIs.push_back(PN);
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for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
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if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i]))
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HandleFloatingPointIV(L, PN);
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// If the loop previously had floating-point IV, ScalarEvolution
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// may not have been able to compute a trip count. Now that we've done some
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// re-writing, the trip count may be computable.
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if (Changed)
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SE->forgetLoopBackedgeTakenCount(L);
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}
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bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
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IU = &getAnalysis<IVUsers>();
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LI = &getAnalysis<LoopInfo>();
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SE = &getAnalysis<ScalarEvolution>();
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Changed = false;
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// If there are any floating-point recurrences, attempt to
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// transform them to use integer recurrences.
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RewriteNonIntegerIVs(L);
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BasicBlock *Header = L->getHeader();
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BasicBlock *ExitingBlock = L->getExitingBlock(); // may be null
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SCEVHandle BackedgeTakenCount = SE->getBackedgeTakenCount(L);
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// Check to see if this loop has a computable loop-invariant execution count.
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// If so, this means that we can compute the final value of any expressions
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// that are recurrent in the loop, and substitute the exit values from the
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// loop into any instructions outside of the loop that use the final values of
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// the current expressions.
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//
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if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
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RewriteLoopExitValues(L, BackedgeTakenCount);
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// Compute the type of the largest recurrence expression, and decide whether
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// a canonical induction variable should be inserted.
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const Type *LargestType = 0;
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bool NeedCannIV = false;
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if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
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LargestType = BackedgeTakenCount->getType();
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LargestType = SE->getEffectiveSCEVType(LargestType);
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// If we have a known trip count and a single exit block, we'll be
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// rewriting the loop exit test condition below, which requires a
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// canonical induction variable.
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if (ExitingBlock)
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NeedCannIV = true;
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}
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for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
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SCEVHandle Stride = IU->StrideOrder[i];
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const Type *Ty = SE->getEffectiveSCEVType(Stride->getType());
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if (!LargestType ||
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SE->getTypeSizeInBits(Ty) >
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SE->getTypeSizeInBits(LargestType))
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LargestType = Ty;
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std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI =
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IU->IVUsesByStride.find(IU->StrideOrder[i]);
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assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
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if (!SI->second->Users.empty())
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NeedCannIV = true;
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}
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// Create a rewriter object which we'll use to transform the code with.
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SCEVExpander Rewriter(*SE);
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// Now that we know the largest of of the induction variable expressions
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// in this loop, insert a canonical induction variable of the largest size.
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Value *IndVar = 0;
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if (NeedCannIV) {
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IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType);
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++NumInserted;
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Changed = true;
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DOUT << "INDVARS: New CanIV: " << *IndVar;
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}
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// If we have a trip count expression, rewrite the loop's exit condition
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// using it. We can currently only handle loops with a single exit.
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ICmpInst *NewICmp = 0;
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if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) && ExitingBlock) {
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assert(NeedCannIV &&
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"LinearFunctionTestReplace requires a canonical induction variable");
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// Can't rewrite non-branch yet.
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if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator()))
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NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
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ExitingBlock, BI, Rewriter);
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}
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Rewriter.setInsertionPoint(Header->getFirstNonPHI());
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// Rewrite IV-derived expressions.
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RewriteIVExpressions(L, LargestType, Rewriter);
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// Loop-invariant instructions in the preheader that aren't used in the
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// loop may be sunk below the loop to reduce register pressure.
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SinkUnusedInvariants(L, Rewriter);
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// Reorder instructions to avoid use-before-def conditions.
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FixUsesBeforeDefs(L, Rewriter);
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// For completeness, inform IVUsers of the IV use in the newly-created
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// loop exit test instruction.
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if (NewICmp)
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IU->AddUsersIfInteresting(cast<Instruction>(NewICmp->getOperand(0)));
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// Clean up dead instructions.
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DeleteDeadPHIs(L->getHeader());
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// Check a post-condition.
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assert(L->isLCSSAForm() && "Indvars did not leave the loop in lcssa form!");
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return Changed;
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}
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void IndVarSimplify::RewriteIVExpressions(Loop *L, const Type *LargestType,
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SCEVExpander &Rewriter) {
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SmallVector<WeakVH, 16> DeadInsts;
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// Rewrite all induction variable expressions in terms of the canonical
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// induction variable.
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//
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// If there were induction variables of other sizes or offsets, manually
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// add the offsets to the primary induction variable and cast, avoiding
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// the need for the code evaluation methods to insert induction variables
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// of different sizes.
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for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
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SCEVHandle Stride = IU->StrideOrder[i];
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std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI =
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IU->IVUsesByStride.find(IU->StrideOrder[i]);
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assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
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ilist<IVStrideUse> &List = SI->second->Users;
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for (ilist<IVStrideUse>::iterator UI = List.begin(),
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E = List.end(); UI != E; ++UI) {
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SCEVHandle Offset = UI->getOffset();
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Value *Op = UI->getOperandValToReplace();
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|
Instruction *User = UI->getUser();
|
|
bool isSigned = UI->isSigned();
|
|
|
|
// Compute the final addrec to expand into code.
|
|
SCEVHandle AR = IU->getReplacementExpr(*UI);
|
|
|
|
// FIXME: It is an extremely bad idea to indvar substitute anything more
|
|
// complex than affine induction variables. Doing so will put expensive
|
|
// polynomial evaluations inside of the loop, and the str reduction pass
|
|
// currently can only reduce affine polynomials. For now just disable
|
|
// indvar subst on anything more complex than an affine addrec, unless
|
|
// it can be expanded to a trivial value.
|
|
if (!Stride->isLoopInvariant(L) &&
|
|
!isa<SCEVConstant>(AR) &&
|
|
L->contains(User->getParent()))
|
|
continue;
|
|
|
|
Value *NewVal = 0;
|
|
if (AR->isLoopInvariant(L)) {
|
|
BasicBlock::iterator I = Rewriter.getInsertionPoint();
|
|
// Expand loop-invariant values in the loop preheader. They will
|
|
// be sunk to the exit block later, if possible.
|
|
NewVal =
|
|
Rewriter.expandCodeFor(AR, LargestType,
|
|
L->getLoopPreheader()->getTerminator());
|
|
Rewriter.setInsertionPoint(I);
|
|
++NumReplaced;
|
|
} else {
|
|
const Type *IVTy = Offset->getType();
|
|
const Type *UseTy = Op->getType();
|
|
|
|
// Promote the Offset and Stride up to the canonical induction
|
|
// variable's bit width.
|
|
SCEVHandle PromotedOffset = Offset;
|
|
SCEVHandle PromotedStride = Stride;
|
|
if (SE->getTypeSizeInBits(IVTy) != SE->getTypeSizeInBits(LargestType)) {
|
|
// It doesn't matter for correctness whether zero or sign extension
|
|
// is used here, since the value is truncated away below, but if the
|
|
// value is signed, sign extension is more likely to be folded.
|
|
if (isSigned) {
|
|
PromotedOffset = SE->getSignExtendExpr(PromotedOffset, LargestType);
|
|
PromotedStride = SE->getSignExtendExpr(PromotedStride, LargestType);
|
|
} else {
|
|
PromotedOffset = SE->getZeroExtendExpr(PromotedOffset, LargestType);
|
|
// If the stride is obviously negative, use sign extension to
|
|
// produce things like x-1 instead of x+255.
|
|
if (isa<SCEVConstant>(PromotedStride) &&
|
|
cast<SCEVConstant>(PromotedStride)
|
|
->getValue()->getValue().isNegative())
|
|
PromotedStride = SE->getSignExtendExpr(PromotedStride,
|
|
LargestType);
|
|
else
|
|
PromotedStride = SE->getZeroExtendExpr(PromotedStride,
|
|
LargestType);
|
|
}
|
|
}
|
|
|
|
// Create the SCEV representing the offset from the canonical
|
|
// induction variable, still in the canonical induction variable's
|
|
// type, so that all expanded arithmetic is done in the same type.
|
|
SCEVHandle NewAR = SE->getAddRecExpr(SE->getIntegerSCEV(0, LargestType),
|
|
PromotedStride, L);
|
|
// Add the PromotedOffset as a separate step, because it may not be
|
|
// loop-invariant.
|
|
NewAR = SE->getAddExpr(NewAR, PromotedOffset);
|
|
|
|
// Expand the addrec into instructions.
|
|
Value *V = Rewriter.expandCodeFor(NewAR);
|
|
|
|
// Insert an explicit cast if necessary to truncate the value
|
|
// down to the original stride type. This is done outside of
|
|
// SCEVExpander because in SCEV expressions, a truncate of an
|
|
// addrec is always folded.
|
|
if (LargestType != IVTy) {
|
|
if (SE->getTypeSizeInBits(IVTy) != SE->getTypeSizeInBits(LargestType))
|
|
NewAR = SE->getTruncateExpr(NewAR, IVTy);
|
|
if (Rewriter.isInsertedExpression(NewAR))
|
|
V = Rewriter.expandCodeFor(NewAR);
|
|
else {
|
|
V = Rewriter.InsertCastOfTo(CastInst::getCastOpcode(V, false,
|
|
IVTy, false),
|
|
V, IVTy);
|
|
assert(!isa<SExtInst>(V) && !isa<ZExtInst>(V) &&
|
|
"LargestType wasn't actually the largest type!");
|
|
// Force the rewriter to use this trunc whenever this addrec
|
|
// appears so that it doesn't insert new phi nodes or
|
|
// arithmetic in a different type.
|
|
Rewriter.addInsertedValue(V, NewAR);
|
|
}
|
|
}
|
|
|
|
DOUT << "INDVARS: Made offset-and-trunc IV for offset "
|
|
<< *IVTy << " " << *Offset << ": ";
|
|
DEBUG(WriteAsOperand(*DOUT, V, false));
|
|
DOUT << "\n";
|
|
|
|
// Now expand it into actual Instructions and patch it into place.
|
|
NewVal = Rewriter.expandCodeFor(AR, UseTy);
|
|
}
|
|
|
|
// Patch the new value into place.
|
|
if (Op->hasName())
|
|
NewVal->takeName(Op);
|
|
User->replaceUsesOfWith(Op, NewVal);
|
|
UI->setOperandValToReplace(NewVal);
|
|
DOUT << "INDVARS: Rewrote IV '" << *AR << "' " << *Op
|
|
<< " into = " << *NewVal << "\n";
|
|
++NumRemoved;
|
|
Changed = true;
|
|
|
|
// The old value may be dead now.
|
|
DeadInsts.push_back(Op);
|
|
}
|
|
}
|
|
|
|
// Now that we're done iterating through lists, clean up any instructions
|
|
// which are now dead.
|
|
while (!DeadInsts.empty()) {
|
|
Instruction *Inst = dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val());
|
|
if (Inst)
|
|
RecursivelyDeleteTriviallyDeadInstructions(Inst);
|
|
}
|
|
}
|
|
|
|
/// If there's a single exit block, sink any loop-invariant values that
|
|
/// were defined in the preheader but not used inside the loop into the
|
|
/// exit block to reduce register pressure in the loop.
|
|
void IndVarSimplify::SinkUnusedInvariants(Loop *L, SCEVExpander &Rewriter) {
|
|
BasicBlock *ExitBlock = L->getExitBlock();
|
|
if (!ExitBlock) return;
|
|
|
|
Instruction *NonPHI = ExitBlock->getFirstNonPHI();
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
BasicBlock::iterator I = Preheader->getTerminator();
|
|
while (I != Preheader->begin()) {
|
|
--I;
|
|
// New instructions were inserted at the end of the preheader. Only
|
|
// consider those new instructions.
|
|
if (!Rewriter.isInsertedInstruction(I))
|
|
break;
|
|
// Determine if there is a use in or before the loop (direct or
|
|
// otherwise).
|
|
bool UsedInLoop = false;
|
|
for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
|
|
UI != UE; ++UI) {
|
|
BasicBlock *UseBB = cast<Instruction>(UI)->getParent();
|
|
if (PHINode *P = dyn_cast<PHINode>(UI)) {
|
|
unsigned i =
|
|
PHINode::getIncomingValueNumForOperand(UI.getOperandNo());
|
|
UseBB = P->getIncomingBlock(i);
|
|
}
|
|
if (UseBB == Preheader || L->contains(UseBB)) {
|
|
UsedInLoop = true;
|
|
break;
|
|
}
|
|
}
|
|
// If there is, the def must remain in the preheader.
|
|
if (UsedInLoop)
|
|
continue;
|
|
// Otherwise, sink it to the exit block.
|
|
Instruction *ToMove = I;
|
|
bool Done = false;
|
|
if (I != Preheader->begin())
|
|
--I;
|
|
else
|
|
Done = true;
|
|
ToMove->moveBefore(NonPHI);
|
|
if (Done)
|
|
break;
|
|
}
|
|
}
|
|
|
|
/// Re-schedule the inserted instructions to put defs before uses. This
|
|
/// fixes problems that arrise when SCEV expressions contain loop-variant
|
|
/// values unrelated to the induction variable which are defined inside the
|
|
/// loop. FIXME: It would be better to insert instructions in the right
|
|
/// place so that this step isn't needed.
|
|
void IndVarSimplify::FixUsesBeforeDefs(Loop *L, SCEVExpander &Rewriter) {
|
|
// Visit all the blocks in the loop in pre-order dom-tree dfs order.
|
|
DominatorTree *DT = &getAnalysis<DominatorTree>();
|
|
std::map<Instruction *, unsigned> NumPredsLeft;
|
|
SmallVector<DomTreeNode *, 16> Worklist;
|
|
Worklist.push_back(DT->getNode(L->getHeader()));
|
|
do {
|
|
DomTreeNode *Node = Worklist.pop_back_val();
|
|
for (DomTreeNode::iterator I = Node->begin(), E = Node->end(); I != E; ++I)
|
|
if (L->contains((*I)->getBlock()))
|
|
Worklist.push_back(*I);
|
|
BasicBlock *BB = Node->getBlock();
|
|
// Visit all the instructions in the block top down.
|
|
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
|
|
// Count the number of operands that aren't properly dominating.
|
|
unsigned NumPreds = 0;
|
|
if (Rewriter.isInsertedInstruction(I) && !isa<PHINode>(I))
|
|
for (User::op_iterator OI = I->op_begin(), OE = I->op_end();
|
|
OI != OE; ++OI)
|
|
if (Instruction *Inst = dyn_cast<Instruction>(OI))
|
|
if (L->contains(Inst->getParent()) && !NumPredsLeft.count(Inst))
|
|
++NumPreds;
|
|
NumPredsLeft[I] = NumPreds;
|
|
// Notify uses of the position of this instruction, and move the
|
|
// users (and their dependents, recursively) into place after this
|
|
// instruction if it is their last outstanding operand.
|
|
for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
|
|
UI != UE; ++UI) {
|
|
Instruction *Inst = cast<Instruction>(UI);
|
|
std::map<Instruction *, unsigned>::iterator Z = NumPredsLeft.find(Inst);
|
|
if (Z != NumPredsLeft.end() && Z->second != 0 && --Z->second == 0) {
|
|
SmallVector<Instruction *, 4> UseWorkList;
|
|
UseWorkList.push_back(Inst);
|
|
BasicBlock::iterator InsertPt = next(I);
|
|
while (isa<PHINode>(InsertPt)) ++InsertPt;
|
|
do {
|
|
Instruction *Use = UseWorkList.pop_back_val();
|
|
Use->moveBefore(InsertPt);
|
|
NumPredsLeft.erase(Use);
|
|
for (Value::use_iterator IUI = Use->use_begin(),
|
|
IUE = Use->use_end(); IUI != IUE; ++IUI) {
|
|
Instruction *IUIInst = cast<Instruction>(IUI);
|
|
if (L->contains(IUIInst->getParent()) &&
|
|
Rewriter.isInsertedInstruction(IUIInst) &&
|
|
!isa<PHINode>(IUIInst))
|
|
UseWorkList.push_back(IUIInst);
|
|
}
|
|
} while (!UseWorkList.empty());
|
|
}
|
|
}
|
|
}
|
|
} while (!Worklist.empty());
|
|
}
|
|
|
|
/// Return true if it is OK to use SIToFPInst for an inducation variable
|
|
/// with given inital and exit values.
|
|
static bool useSIToFPInst(ConstantFP &InitV, ConstantFP &ExitV,
|
|
uint64_t intIV, uint64_t intEV) {
|
|
|
|
if (InitV.getValueAPF().isNegative() || ExitV.getValueAPF().isNegative())
|
|
return true;
|
|
|
|
// If the iteration range can be handled by SIToFPInst then use it.
|
|
APInt Max = APInt::getSignedMaxValue(32);
|
|
if (Max.getZExtValue() > static_cast<uint64_t>(abs64(intEV - intIV)))
|
|
return true;
|
|
|
|
return false;
|
|
}
|
|
|
|
/// convertToInt - Convert APF to an integer, if possible.
|
|
static bool convertToInt(const APFloat &APF, uint64_t *intVal) {
|
|
|
|
bool isExact = false;
|
|
if (&APF.getSemantics() == &APFloat::PPCDoubleDouble)
|
|
return false;
|
|
if (APF.convertToInteger(intVal, 32, APF.isNegative(),
|
|
APFloat::rmTowardZero, &isExact)
|
|
!= APFloat::opOK)
|
|
return false;
|
|
if (!isExact)
|
|
return false;
|
|
return true;
|
|
|
|
}
|
|
|
|
/// HandleFloatingPointIV - If the loop has floating induction variable
|
|
/// then insert corresponding integer induction variable if possible.
|
|
/// For example,
|
|
/// for(double i = 0; i < 10000; ++i)
|
|
/// bar(i)
|
|
/// is converted into
|
|
/// for(int i = 0; i < 10000; ++i)
|
|
/// bar((double)i);
|
|
///
|
|
void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PH) {
|
|
|
|
unsigned IncomingEdge = L->contains(PH->getIncomingBlock(0));
|
|
unsigned BackEdge = IncomingEdge^1;
|
|
|
|
// Check incoming value.
|
|
ConstantFP *InitValue = dyn_cast<ConstantFP>(PH->getIncomingValue(IncomingEdge));
|
|
if (!InitValue) return;
|
|
uint64_t newInitValue = Type::Int32Ty->getPrimitiveSizeInBits();
|
|
if (!convertToInt(InitValue->getValueAPF(), &newInitValue))
|
|
return;
|
|
|
|
// Check IV increment. Reject this PH if increement operation is not
|
|
// an add or increment value can not be represented by an integer.
|
|
BinaryOperator *Incr =
|
|
dyn_cast<BinaryOperator>(PH->getIncomingValue(BackEdge));
|
|
if (!Incr) return;
|
|
if (Incr->getOpcode() != Instruction::Add) return;
|
|
ConstantFP *IncrValue = NULL;
|
|
unsigned IncrVIndex = 1;
|
|
if (Incr->getOperand(1) == PH)
|
|
IncrVIndex = 0;
|
|
IncrValue = dyn_cast<ConstantFP>(Incr->getOperand(IncrVIndex));
|
|
if (!IncrValue) return;
|
|
uint64_t newIncrValue = Type::Int32Ty->getPrimitiveSizeInBits();
|
|
if (!convertToInt(IncrValue->getValueAPF(), &newIncrValue))
|
|
return;
|
|
|
|
// Check Incr uses. One user is PH and the other users is exit condition used
|
|
// by the conditional terminator.
|
|
Value::use_iterator IncrUse = Incr->use_begin();
|
|
Instruction *U1 = cast<Instruction>(IncrUse++);
|
|
if (IncrUse == Incr->use_end()) return;
|
|
Instruction *U2 = cast<Instruction>(IncrUse++);
|
|
if (IncrUse != Incr->use_end()) return;
|
|
|
|
// Find exit condition.
|
|
FCmpInst *EC = dyn_cast<FCmpInst>(U1);
|
|
if (!EC)
|
|
EC = dyn_cast<FCmpInst>(U2);
|
|
if (!EC) return;
|
|
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(EC->getParent()->getTerminator())) {
|
|
if (!BI->isConditional()) return;
|
|
if (BI->getCondition() != EC) return;
|
|
}
|
|
|
|
// Find exit value. If exit value can not be represented as an interger then
|
|
// do not handle this floating point PH.
|
|
ConstantFP *EV = NULL;
|
|
unsigned EVIndex = 1;
|
|
if (EC->getOperand(1) == Incr)
|
|
EVIndex = 0;
|
|
EV = dyn_cast<ConstantFP>(EC->getOperand(EVIndex));
|
|
if (!EV) return;
|
|
uint64_t intEV = Type::Int32Ty->getPrimitiveSizeInBits();
|
|
if (!convertToInt(EV->getValueAPF(), &intEV))
|
|
return;
|
|
|
|
// Find new predicate for integer comparison.
|
|
CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
|
|
switch (EC->getPredicate()) {
|
|
case CmpInst::FCMP_OEQ:
|
|
case CmpInst::FCMP_UEQ:
|
|
NewPred = CmpInst::ICMP_EQ;
|
|
break;
|
|
case CmpInst::FCMP_OGT:
|
|
case CmpInst::FCMP_UGT:
|
|
NewPred = CmpInst::ICMP_UGT;
|
|
break;
|
|
case CmpInst::FCMP_OGE:
|
|
case CmpInst::FCMP_UGE:
|
|
NewPred = CmpInst::ICMP_UGE;
|
|
break;
|
|
case CmpInst::FCMP_OLT:
|
|
case CmpInst::FCMP_ULT:
|
|
NewPred = CmpInst::ICMP_ULT;
|
|
break;
|
|
case CmpInst::FCMP_OLE:
|
|
case CmpInst::FCMP_ULE:
|
|
NewPred = CmpInst::ICMP_ULE;
|
|
break;
|
|
default:
|
|
break;
|
|
}
|
|
if (NewPred == CmpInst::BAD_ICMP_PREDICATE) return;
|
|
|
|
// Insert new integer induction variable.
|
|
PHINode *NewPHI = PHINode::Create(Type::Int32Ty,
|
|
PH->getName()+".int", PH);
|
|
NewPHI->addIncoming(ConstantInt::get(Type::Int32Ty, newInitValue),
|
|
PH->getIncomingBlock(IncomingEdge));
|
|
|
|
Value *NewAdd = BinaryOperator::CreateAdd(NewPHI,
|
|
ConstantInt::get(Type::Int32Ty,
|
|
newIncrValue),
|
|
Incr->getName()+".int", Incr);
|
|
NewPHI->addIncoming(NewAdd, PH->getIncomingBlock(BackEdge));
|
|
|
|
// The back edge is edge 1 of newPHI, whatever it may have been in the
|
|
// original PHI.
|
|
ConstantInt *NewEV = ConstantInt::get(Type::Int32Ty, intEV);
|
|
Value *LHS = (EVIndex == 1 ? NewPHI->getIncomingValue(1) : NewEV);
|
|
Value *RHS = (EVIndex == 1 ? NewEV : NewPHI->getIncomingValue(1));
|
|
ICmpInst *NewEC = new ICmpInst(NewPred, LHS, RHS, EC->getNameStart(),
|
|
EC->getParent()->getTerminator());
|
|
|
|
// In the following deltions, PH may become dead and may be deleted.
|
|
// Use a WeakVH to observe whether this happens.
|
|
WeakVH WeakPH = PH;
|
|
|
|
// Delete old, floating point, exit comparision instruction.
|
|
EC->replaceAllUsesWith(NewEC);
|
|
RecursivelyDeleteTriviallyDeadInstructions(EC);
|
|
|
|
// Delete old, floating point, increment instruction.
|
|
Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
|
|
RecursivelyDeleteTriviallyDeadInstructions(Incr);
|
|
|
|
// Replace floating induction variable, if it isn't already deleted.
|
|
// Give SIToFPInst preference over UIToFPInst because it is faster on
|
|
// platforms that are widely used.
|
|
if (WeakPH && !PH->use_empty()) {
|
|
if (useSIToFPInst(*InitValue, *EV, newInitValue, intEV)) {
|
|
SIToFPInst *Conv = new SIToFPInst(NewPHI, PH->getType(), "indvar.conv",
|
|
PH->getParent()->getFirstNonPHI());
|
|
PH->replaceAllUsesWith(Conv);
|
|
} else {
|
|
UIToFPInst *Conv = new UIToFPInst(NewPHI, PH->getType(), "indvar.conv",
|
|
PH->getParent()->getFirstNonPHI());
|
|
PH->replaceAllUsesWith(Conv);
|
|
}
|
|
RecursivelyDeleteTriviallyDeadInstructions(PH);
|
|
}
|
|
|
|
// Add a new IVUsers entry for the newly-created integer PHI.
|
|
IU->AddUsersIfInteresting(NewPHI);
|
|
}
|