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

1 files changed, 1 insertions, 10 deletions

diff --git a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
index 0f8f6d28e4f..44e72e2232c 100644
--- a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
+++ b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
@@ -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;
   }