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Give up on doing in-line instruction simplification during correlated value propagation. Instruction simplification 

needs to be guaranteed never to be run on an unreachable block.  However, earlier block simplifications may have
changed the CFG to make block that were reachable when we began our iteration unreachable by the time we try to
simplify them. (Note that this also means that our depth-first iterators were potentially being invalidated).

This should not have a large impact on code quality, since later runs of instcombine should pick up these simplifications.
Fixes PR8506.

llvm-svn: 117709
This commit is contained in:
Owen Anderson 2010-10-29 21:05:17 +00:00
parent 72dfc6a7c7
commit 374e1464ae
1 changed files with 1 additions and 10 deletions
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11
llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
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@ -19,7 +19,6 @@
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/Support/CFG.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
@ -172,10 +171,7 @@ bool CorrelatedValuePropagation::runOnFunction(Function &F) {
bool FnChanged = false;
// Perform a depth-first walk of the CFG so that we don't waste time
// optimizing unreachable blocks.
for (df_iterator<BasicBlock*> FI = df_begin(&F.getEntryBlock()),
FE = df_end(&F.getEntryBlock()); FI != FE; ++FI) {
for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
bool BBChanged = false;
for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
Instruction *II = BI++;
@ -197,11 +193,6 @@ bool CorrelatedValuePropagation::runOnFunction(Function &F) {
}
}
// Propagating correlated values might leave cruft around.
// Try to clean it up before we continue.
if (BBChanged)
SimplifyInstructionsInBlock(*FI);
FnChanged |= BBChanged;
}