mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-19 19:29:31 +00:00
Rewrite the GCSE pass to be *substantially* simpler, a bit more efficient,
and a bit more powerful git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12817 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
parent
326c0f3013
commit
38e66bd9d1
@ -15,14 +15,15 @@
|
||||
//===----------------------------------------------------------------------===//
|
||||
|
||||
#include "llvm/Transforms/Scalar.h"
|
||||
#include "llvm/iMemory.h"
|
||||
#include "llvm/iOther.h"
|
||||
#include "llvm/BasicBlock.h"
|
||||
#include "llvm/Constant.h"
|
||||
#include "llvm/Instructions.h"
|
||||
#include "llvm/Type.h"
|
||||
#include "llvm/Analysis/Dominators.h"
|
||||
#include "llvm/Analysis/ValueNumbering.h"
|
||||
#include "llvm/Support/InstIterator.h"
|
||||
#include "llvm/Transforms/Utils/Local.h"
|
||||
#include "Support/DepthFirstIterator.h"
|
||||
#include "Support/Statistic.h"
|
||||
#include "Support/Debug.h"
|
||||
#include <algorithm>
|
||||
using namespace llvm;
|
||||
|
||||
@ -33,23 +34,17 @@ namespace {
|
||||
Statistic<> NumNonInsts ("gcse", "Number of instructions removed due "
|
||||
"to non-instruction values");
|
||||
|
||||
class GCSE : public FunctionPass {
|
||||
std::set<Instruction*> WorkList;
|
||||
DominatorSet *DomSetInfo;
|
||||
ValueNumbering *VN;
|
||||
public:
|
||||
struct GCSE : public FunctionPass {
|
||||
virtual bool runOnFunction(Function &F);
|
||||
|
||||
private:
|
||||
bool EliminateRedundancies(Instruction *I,std::vector<Value*> &EqualValues);
|
||||
Instruction *EliminateCSE(Instruction *I, Instruction *Other);
|
||||
void ReplaceInstWithInst(Instruction *First, BasicBlock::iterator SI);
|
||||
void ReplaceInstructionWith(Instruction *I, Value *V);
|
||||
|
||||
// This transformation requires dominator and immediate dominator info
|
||||
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
|
||||
AU.setPreservesCFG();
|
||||
AU.addRequired<DominatorSet>();
|
||||
AU.addRequired<ImmediateDominators>();
|
||||
AU.addRequired<DominatorTree>();
|
||||
AU.addRequired<ValueNumbering>();
|
||||
}
|
||||
};
|
||||
@ -67,32 +62,89 @@ bool GCSE::runOnFunction(Function &F) {
|
||||
bool Changed = false;
|
||||
|
||||
// Get pointers to the analysis results that we will be using...
|
||||
DomSetInfo = &getAnalysis<DominatorSet>();
|
||||
VN = &getAnalysis<ValueNumbering>();
|
||||
DominatorSet &DS = getAnalysis<DominatorSet>();
|
||||
ValueNumbering &VN = getAnalysis<ValueNumbering>();
|
||||
DominatorTree &DT = getAnalysis<DominatorTree>();
|
||||
|
||||
// Step #1: Add all instructions in the function to the worklist for
|
||||
// processing. All of the instructions are considered to be our
|
||||
// subexpressions to eliminate if possible.
|
||||
//
|
||||
WorkList.insert(inst_begin(F), inst_end(F));
|
||||
std::vector<Value*> EqualValues;
|
||||
|
||||
// Step #2: WorkList processing. Iterate through all of the instructions,
|
||||
// checking to see if there are any additionally defined subexpressions in the
|
||||
// program. If so, eliminate them!
|
||||
//
|
||||
while (!WorkList.empty()) {
|
||||
Instruction &I = **WorkList.begin(); // Get an instruction from the worklist
|
||||
WorkList.erase(WorkList.begin());
|
||||
// Traverse the CFG of the function in dominator order, so that we see each
|
||||
// instruction after we see its operands.
|
||||
for (df_iterator<DominatorTree::Node*> DI = df_begin(DT.getRootNode()),
|
||||
E = df_end(DT.getRootNode()); DI != E; ++DI) {
|
||||
BasicBlock *BB = DI->getBlock();
|
||||
|
||||
// If this instruction computes a value, try to fold together common
|
||||
// instructions that compute it.
|
||||
//
|
||||
if (I.getType() != Type::VoidTy) {
|
||||
std::vector<Value*> EqualValues;
|
||||
VN->getEqualNumberNodes(&I, EqualValues);
|
||||
// Remember which instructions we've seen in this basic block as we scan.
|
||||
std::set<Instruction*> BlockInsts;
|
||||
|
||||
if (!EqualValues.empty())
|
||||
Changed |= EliminateRedundancies(&I, EqualValues);
|
||||
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
|
||||
Instruction *Inst = I++;
|
||||
|
||||
// If this instruction computes a value, try to fold together common
|
||||
// instructions that compute it.
|
||||
//
|
||||
if (Inst->getType() != Type::VoidTy) {
|
||||
VN.getEqualNumberNodes(Inst, EqualValues);
|
||||
|
||||
// If this instruction computes a value that is already computed
|
||||
// elsewhere, try to recycle the old value.
|
||||
if (!EqualValues.empty()) {
|
||||
if (Inst == &*BB->begin())
|
||||
I = BB->end();
|
||||
else {
|
||||
I = Inst; --I;
|
||||
}
|
||||
|
||||
// First check to see if we were able to value number this instruction
|
||||
// to a non-instruction value. If so, prefer that value over other
|
||||
// instructions which may compute the same thing.
|
||||
for (unsigned i = 0, e = EqualValues.size(); i != e; ++i)
|
||||
if (!isa<Instruction>(EqualValues[i])) {
|
||||
++NumNonInsts; // Keep track of # of insts repl with values
|
||||
|
||||
// Change all users of Inst to use the replacement and remove it
|
||||
// from the program.
|
||||
ReplaceInstructionWith(Inst, EqualValues[i]);
|
||||
Inst = 0;
|
||||
EqualValues.clear(); // don't enter the next loop
|
||||
break;
|
||||
}
|
||||
|
||||
// If there were no non-instruction values that this instruction
|
||||
// produces, find a dominating instruction that produces the same
|
||||
// value. If we find one, use it's value instead of ours.
|
||||
for (unsigned i = 0, e = EqualValues.size(); i != e; ++i) {
|
||||
Instruction *OtherI = cast<Instruction>(EqualValues[i]);
|
||||
bool Dominates = false;
|
||||
if (OtherI->getParent() == BB)
|
||||
Dominates = BlockInsts.count(OtherI);
|
||||
else
|
||||
Dominates = DS.dominates(OtherI->getParent(), BB);
|
||||
|
||||
if (Dominates) {
|
||||
// Okay, we found an instruction with the same value as this one
|
||||
// and that dominates this one. Replace this instruction with the
|
||||
// specified one.
|
||||
ReplaceInstructionWith(Inst, OtherI);
|
||||
Inst = 0;
|
||||
break;
|
||||
}
|
||||
}
|
||||
|
||||
EqualValues.clear();
|
||||
|
||||
if (Inst) {
|
||||
I = Inst; ++I; // Deleted no instructions
|
||||
} else if (I == BB->end()) { // Deleted first instruction
|
||||
I = BB->begin();
|
||||
} else { // Deleted inst in middle of block.
|
||||
++I;
|
||||
}
|
||||
}
|
||||
|
||||
if (Inst)
|
||||
BlockInsts.insert(Inst);
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
@ -100,193 +152,48 @@ bool GCSE::runOnFunction(Function &F) {
|
||||
return Changed;
|
||||
}
|
||||
|
||||
bool GCSE::EliminateRedundancies(Instruction *I,
|
||||
std::vector<Value*> &EqualValues) {
|
||||
// If the EqualValues set contains any non-instruction values, then we know
|
||||
// that all of the instructions can be replaced with the non-instruction value
|
||||
// because it is guaranteed to dominate all of the instructions in the
|
||||
// function. We only have to do hard work if all we have are instructions.
|
||||
//
|
||||
for (unsigned i = 0, e = EqualValues.size(); i != e; ++i)
|
||||
if (!isa<Instruction>(EqualValues[i])) {
|
||||
// Found a non-instruction. Replace all instructions with the
|
||||
// non-instruction.
|
||||
//
|
||||
Value *Replacement = EqualValues[i];
|
||||
|
||||
// Make sure we get I as well...
|
||||
EqualValues[i] = I;
|
||||
void GCSE::ReplaceInstructionWith(Instruction *I, Value *V) {
|
||||
if (isa<LoadInst>(I))
|
||||
++NumLoadRemoved; // Keep track of loads eliminated
|
||||
if (isa<CallInst>(I))
|
||||
++NumCallRemoved; // Keep track of calls eliminated
|
||||
++NumInstRemoved; // Keep track of number of insts eliminated
|
||||
|
||||
// Replace all instructions with the Replacement value.
|
||||
for (i = 0; i != e; ++i)
|
||||
if (Instruction *I = dyn_cast<Instruction>(EqualValues[i])) {
|
||||
// Change all users of I to use Replacement.
|
||||
I->replaceAllUsesWith(Replacement);
|
||||
// If we are not replacing the instruction with a constant, we cannot do
|
||||
// anything special.
|
||||
if (!isa<Constant>(V)) {
|
||||
I->replaceAllUsesWith(V);
|
||||
|
||||
if (isa<LoadInst>(I))
|
||||
++NumLoadRemoved; // Keep track of loads eliminated
|
||||
if (isa<CallInst>(I))
|
||||
++NumCallRemoved; // Keep track of calls eliminated
|
||||
++NumInstRemoved; // Keep track of number of instructions eliminated
|
||||
++NumNonInsts; // Keep track of number of insts repl with values
|
||||
// Erase the instruction from the program.
|
||||
I->getParent()->getInstList().erase(I);
|
||||
return;
|
||||
}
|
||||
|
||||
// Erase the instruction from the program.
|
||||
I->getParent()->getInstList().erase(I);
|
||||
WorkList.erase(I);
|
||||
}
|
||||
|
||||
return true;
|
||||
}
|
||||
Constant *C = cast<Constant>(V);
|
||||
std::vector<User*> Users(I->use_begin(), I->use_end());
|
||||
|
||||
// Perform the replacement.
|
||||
I->replaceAllUsesWith(C);
|
||||
|
||||
// Erase the instruction from the program.
|
||||
I->getParent()->getInstList().erase(I);
|
||||
|
||||
// Remove duplicate entries from EqualValues...
|
||||
std::sort(EqualValues.begin(), EqualValues.end());
|
||||
EqualValues.erase(std::unique(EqualValues.begin(), EqualValues.end()),
|
||||
EqualValues.end());
|
||||
// Check each user to see if we can constant fold it.
|
||||
while (!Users.empty()) {
|
||||
Instruction *U = cast<Instruction>(Users.back());
|
||||
Users.pop_back();
|
||||
|
||||
// From this point on, EqualValues is logically a vector of instructions.
|
||||
//
|
||||
bool Changed = false;
|
||||
EqualValues.push_back(I); // Make sure I is included...
|
||||
while (EqualValues.size() > 1) {
|
||||
// FIXME, this could be done better than simple iteration!
|
||||
Instruction *Test = cast<Instruction>(EqualValues.back());
|
||||
EqualValues.pop_back();
|
||||
|
||||
for (unsigned i = 0, e = EqualValues.size(); i != e; ++i)
|
||||
if (Instruction *Ret = EliminateCSE(Test,
|
||||
cast<Instruction>(EqualValues[i]))) {
|
||||
if (Ret == Test) // Eliminated EqualValues[i]
|
||||
EqualValues[i] = Test; // Make sure that we reprocess I at some point
|
||||
Changed = true;
|
||||
break;
|
||||
if (Constant *C = ConstantFoldInstruction(U)) {
|
||||
ReplaceInstructionWith(U, C);
|
||||
|
||||
// If the instruction used I more than once, it could be on the user list
|
||||
// multiple times. Make sure we don't reprocess it.
|
||||
std::vector<User*>::iterator It = std::find(Users.begin(), Users.end(),U);
|
||||
while (It != Users.end()) {
|
||||
Users.erase(It);
|
||||
It = std::find(Users.begin(), Users.end(), U);
|
||||
}
|
||||
}
|
||||
return Changed;
|
||||
}
|
||||
|
||||
|
||||
// ReplaceInstWithInst - Destroy the instruction pointed to by SI, making all
|
||||
// uses of the instruction use First now instead.
|
||||
//
|
||||
void GCSE::ReplaceInstWithInst(Instruction *First, BasicBlock::iterator SI) {
|
||||
Instruction &Second = *SI;
|
||||
|
||||
DEBUG(std::cerr << "GCSE: Substituting %" << First->getName() << " for: "
|
||||
<< Second);
|
||||
|
||||
//cerr << "DEL " << (void*)Second << Second;
|
||||
|
||||
// Add the first instruction back to the worklist
|
||||
WorkList.insert(First);
|
||||
|
||||
// Add all uses of the second instruction to the worklist
|
||||
for (Value::use_iterator UI = Second.use_begin(), UE = Second.use_end();
|
||||
UI != UE; ++UI)
|
||||
WorkList.insert(cast<Instruction>(*UI));
|
||||
|
||||
// Make all users of 'Second' now use 'First'
|
||||
Second.replaceAllUsesWith(First);
|
||||
|
||||
// Erase the second instruction from the program
|
||||
Second.getParent()->getInstList().erase(SI);
|
||||
}
|
||||
|
||||
// EliminateCSE - The two instruction I & Other have been found to be common
|
||||
// subexpressions. This function is responsible for eliminating one of them,
|
||||
// and for fixing the worklist to be correct. The instruction that is preserved
|
||||
// is returned from the function if the other is eliminated, otherwise null is
|
||||
// returned.
|
||||
//
|
||||
Instruction *GCSE::EliminateCSE(Instruction *I, Instruction *Other) {
|
||||
assert(I != Other);
|
||||
|
||||
WorkList.erase(I);
|
||||
WorkList.erase(Other); // Other may not actually be on the worklist anymore...
|
||||
|
||||
// Handle the easy case, where both instructions are in the same basic block
|
||||
BasicBlock *BB1 = I->getParent(), *BB2 = Other->getParent();
|
||||
Instruction *Ret = 0;
|
||||
|
||||
if (BB1 == BB2) {
|
||||
// Eliminate the second occurring instruction. Add all uses of the second
|
||||
// instruction to the worklist.
|
||||
//
|
||||
// Scan the basic block looking for the "first" instruction
|
||||
BasicBlock::iterator BI = BB1->begin();
|
||||
while (&*BI != I && &*BI != Other) {
|
||||
++BI;
|
||||
assert(BI != BB1->end() && "Instructions not found in parent BB!");
|
||||
}
|
||||
|
||||
// Keep track of which instructions occurred first & second
|
||||
Instruction *First = BI;
|
||||
Instruction *Second = I != First ? I : Other; // Get iterator to second inst
|
||||
BI = Second;
|
||||
|
||||
if (isa<LoadInst>(Second))
|
||||
++NumLoadRemoved; // Keep track of loads eliminated
|
||||
if (isa<CallInst>(Second))
|
||||
++NumCallRemoved; // Keep track of calls eliminated
|
||||
|
||||
// Destroy Second, using First instead.
|
||||
ReplaceInstWithInst(First, BI);
|
||||
Ret = First;
|
||||
|
||||
// Otherwise, the two instructions are in different basic blocks. If one
|
||||
// dominates the other instruction, we can simply use it
|
||||
//
|
||||
} else if (DomSetInfo->dominates(BB1, BB2)) { // I dom Other?
|
||||
if (isa<LoadInst>(Other))
|
||||
++NumLoadRemoved; // Keep track of loads eliminated
|
||||
if (isa<CallInst>(Other))
|
||||
++NumCallRemoved; // Keep track of calls eliminated
|
||||
|
||||
ReplaceInstWithInst(I, Other);
|
||||
Ret = I;
|
||||
} else if (DomSetInfo->dominates(BB2, BB1)) { // Other dom I?
|
||||
if (isa<LoadInst>(I))
|
||||
++NumLoadRemoved; // Keep track of loads eliminated
|
||||
if (isa<CallInst>(I))
|
||||
++NumCallRemoved; // Keep track of calls eliminated
|
||||
|
||||
ReplaceInstWithInst(Other, I);
|
||||
Ret = Other;
|
||||
} else {
|
||||
// This code is disabled because it has several problems:
|
||||
// One, the actual assumption is wrong, as shown by this code:
|
||||
// int "test"(int %X, int %Y) {
|
||||
// %Z = add int %X, %Y
|
||||
// ret int %Z
|
||||
// Unreachable:
|
||||
// %Q = add int %X, %Y
|
||||
// ret int %Q
|
||||
// }
|
||||
//
|
||||
// Here there are no shared dominators. Additionally, this had the habit of
|
||||
// moving computations where they were not always computed. For example, in
|
||||
// a case like this:
|
||||
// if (c) {
|
||||
// if (d) ...
|
||||
// else ... X+Y ...
|
||||
// } else {
|
||||
// ... X+Y ...
|
||||
// }
|
||||
//
|
||||
// In this case, the expression would be hoisted to outside the 'if' stmt,
|
||||
// causing the expression to be evaluated, even for the if (d) path, which
|
||||
// could cause problems, if, for example, it caused a divide by zero. In
|
||||
// general the problem this case is trying to solve is better addressed with
|
||||
// PRE than GCSE.
|
||||
//
|
||||
return 0;
|
||||
}
|
||||
|
||||
++NumInstRemoved; // Keep track of number of instructions eliminated
|
||||
|
||||
// Add all users of Ret to the worklist...
|
||||
for (Value::use_iterator I = Ret->use_begin(), E = Ret->use_end(); I != E;++I)
|
||||
if (Instruction *Inst = dyn_cast<Instruction>(*I))
|
||||
WorkList.insert(Inst);
|
||||
|
||||
return Ret;
|
||||
}
|
||||
|
Loading…
Reference in New Issue
Block a user