[llvm-commits] [llvm] r122343 - /llvm/trunk/lib/Transforms/Utils/SimplifyInstructions.cpp
Duncan Sands
baldrick at free.fr
Tue Dec 21 09:08:55 PST 2010
Author: baldrick
Date: Tue Dec 21 11:08:55 2010
New Revision: 122343
URL: http://llvm.org/viewvc/llvm-project?rev=122343&view=rev
Log:
Visit instructions deterministically. Use a FIFO so as to approximately
visit instructions before their uses, since InstructionSimplify does a
better job in that case. All this prompted by Frits van Bommel.
Modified:
llvm/trunk/lib/Transforms/Utils/SimplifyInstructions.cpp
Modified: llvm/trunk/lib/Transforms/Utils/SimplifyInstructions.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyInstructions.cpp?rev=122343&r1=122342&r2=122343&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyInstructions.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyInstructions.cpp Tue Dec 21 11:08:55 2010
@@ -24,6 +24,7 @@
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
+#include <queue>
using namespace llvm;
STATISTIC(NumSimplified, "Number of redundant instructions removed");
@@ -45,8 +46,9 @@
const DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>();
bool Changed = false;
- // Add all interesting instructions to the worklist.
- std::set<Instruction*> Worklist;
+ // Add all interesting instructions to the worklist. These are processed
+ // in FIFO order, so instructions are usually visited before their uses.
+ std::queue<Instruction*> Worklist;
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
Instruction *I = BI++;
@@ -57,30 +59,38 @@
continue;
}
// Add all others to the worklist.
- Worklist.insert(I);
+ Worklist.push(I);
}
// Simplify everything in the worklist until the cows come home.
while (!Worklist.empty()) {
- Instruction *I = *Worklist.begin();
- Worklist.erase(Worklist.begin());
+ Instruction *I = Worklist.front();
+ Worklist.pop();
+ // Don't bother simplifying unused instructions.
+ if (I->use_empty()) continue;
Value *V = SimplifyInstruction(I, TD, DT);
if (!V) continue;
// This instruction simplifies! Replace it with its simplification and
// add all uses to the worklist, since they may now simplify.
+ ++NumSimplified;
I->replaceAllUsesWith(V);
for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
UI != UE; ++UI)
- // In unreachable code an instruction can use itself, in which case
- // don't add it to the worklist since we are about to erase it.
- if (*UI != I) Worklist.insert(cast<Instruction>(*UI));
- if (isInstructionTriviallyDead(I))
- I->eraseFromParent();
- ++NumSimplified;
+ Worklist.push(cast<Instruction>(*UI));
Changed = true;
}
+ // Finally, run over the function zapping any dead instructions.
+ for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
+ for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
+ Instruction *I = BI++;
+ if (isInstructionTriviallyDead(I)) {
+ I->eraseFromParent();
+ Changed = true;
+ }
+ }
+
return Changed;
}
};
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