Refine the change in r52258 for avoiding use-before-def conditions
when changing the stride of a comparison so that it's slightly
more precise, by having it scan the instruction list to determine
if there is a use of the condition after the point where the
condition will be inserted.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52371 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index e9976c5..f447292 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -1530,15 +1530,6 @@
ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond,
IVStrideUse* &CondUse,
const SCEVHandle* &CondStride) {
- // Forgo this transformation if the condition has multiple uses. This is
- // over-conservative, but simpler than alternatives. It guards against
- // comparisons with a use that occurs earlier than the add instruction for the
- // new stride index. See
- // test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness.ll
- // for an example of this situation.
- if (!Cond->hasOneUse())
- return Cond;
-
if (StrideOrder.size() < 2 ||
IVUsesByStride[*CondStride].Users.size() != 1)
return Cond;
@@ -1653,6 +1644,18 @@
}
}
+ // Forgo this transformation if it the increment happens to be
+ // unfortunately positioned after the condition, and the condition
+ // has multiple uses which prevent it from being moved immediately
+ // before the branch. See
+ // test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness-*.ll
+ // for an example of this situation.
+ if (!Cond->hasOneUse())
+ for (BasicBlock::iterator I = Cond, E = Cond->getParent()->end();
+ I != E; ++I)
+ if (I == NewIncV)
+ return Cond;
+
if (NewCmpVal != CmpVal) {
// Create a new compare instruction using new stride / iv.
ICmpInst *OldCond = Cond;