BBVectorize: Add initial stores to the write set when tracking uses

When computing the use set of a store, we need to add the store to the write
set prior to iterating over later instructions. Otherwise, if there is a later
aliasing load of that store, that load will not be tagged as a use, and bad
things will happen.

trackUsesOfI still adds later dependent stores of an instruction to that
instruction's write set, but it never sees the original instruction, and so
when tracking uses of a store, the store must be added to the write set by the
caller.

Fixes PR16834.

llvm-svn: 188329

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Vectorize/BBVectorize.cpp b/llvm/lib/Transforms/Vectorize/BBVectorize.cpp
index cbc1d630d52..83ee1a459f0 100644
--- a/llvm/lib/Transforms/Vectorize/BBVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/BBVectorize.cpp
@@ -1182,6 +1182,8 @@ namespace {
       // Look for an instruction with which to pair instruction *I...
       DenseSet<Value *> Users;
       AliasSetTracker WriteSet(*AA);
+      if (I->mayWriteToMemory()) WriteSet.add(I);
+
       bool JAfterStart = IAfterStart;
       BasicBlock::iterator J = llvm::next(I);
       for (unsigned ss = 0; J != E && ss <= Config.SearchLimit; ++J, ++ss) {
@@ -1403,6 +1405,8 @@ namespace {
 
       DenseSet<Value *> Users;
       AliasSetTracker WriteSet(*AA);
+      if (I->mayWriteToMemory()) WriteSet.add(I);
+
       for (BasicBlock::iterator J = llvm::next(I); J != E; ++J) {
         (void) trackUsesOfI(Users, WriteSet, I, J);
 
@@ -2804,6 +2808,8 @@ namespace {
 
     DenseSet<Value *> Users;
     AliasSetTracker WriteSet(*AA);
+    if (I->mayWriteToMemory()) WriteSet.add(I);
+
     for (; cast<Instruction>(L) != J; ++L)
       (void) trackUsesOfI(Users, WriteSet, I, L, true, &LoadMoveSetPairs);
 
@@ -2824,6 +2830,8 @@ namespace {
 
     DenseSet<Value *> Users;
     AliasSetTracker WriteSet(*AA);
+    if (I->mayWriteToMemory()) WriteSet.add(I);
+
     for (; cast<Instruction>(L) != J;) {
       if (trackUsesOfI(Users, WriteSet, I, L, true, &LoadMoveSetPairs)) {
         // Move this instruction
@@ -2853,6 +2861,7 @@ namespace {
 
     DenseSet<Value *> Users;
     AliasSetTracker WriteSet(*AA);
+    if (I->mayWriteToMemory()) WriteSet.add(I);
 
     // Note: We cannot end the loop when we reach J because J could be moved
     // farther down the use chain by another instruction pairing. Also, J