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PRE requires that critical edges be split.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52505 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2008-06-19 19:54:19 +00:00
parent ac151da204
commit 5c274eebc6
1 changed files with 24 additions and 0 deletions
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24
lib/Transforms/Scalar/GVN.cpp
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@ -34,6 +34,7 @@
#include "llvm/Support/CFG.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
STATISTIC(NumGVNInstr, "Number of instructions deleted");
@ -1128,6 +1129,7 @@ bool GVN::processBlock(DomTreeNode* DTN) {
/// control flow patterns and attempts to perform simple PRE at the join point.
bool GVN::performPRE(Function& F) {
bool changed = false;
SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
BasicBlock* CurrentBlock = *DI;
@ -1179,6 +1181,24 @@ bool GVN::performPRE(Function& F) {
continue;
}
// We can't do PRE safely on a critical edge, so instead we schedule
// the edge to be split and perform the PRE the next time we iterate
// on the function.
unsigned succNum = 0;
for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
i != e; ++i)
if (PREPred->getTerminator()->getSuccessor(i) == PREPred) {
succNum = i;
break;
}
if (isCriticalEdge(PREPred->getTerminator(), succNum)) {
toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum));
changed = true;
BI++;
continue;
}
// Instantiate the expression the in predecessor that lacked it.
// Because we are going top-down through the block, all value numbers
// will be available in the predecessor by the time we need them. Any
@ -1244,6 +1264,10 @@ bool GVN::performPRE(Function& F) {
}
}
for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
SplitCriticalEdge(I->first, I->second, this);
return changed;
}