Protect ChangeCompareStride from situations in which it is possible
for it to generate use-before-def IR, such as in this testcase.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52258 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index cc5da5d..1955fa5 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -1529,6 +1529,15 @@
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;
@@ -1654,9 +1663,9 @@
RHS = SCEVExpander::InsertCastOfTo(Instruction::IntToPtr, RHS, NewCmpTy);
}
// Insert new compare instruction.
- Cond = new ICmpInst(Predicate, NewIncV, RHS);
- Cond->setName(L->getHeader()->getName() + ".termcond");
- OldCond->getParent()->getInstList().insert(OldCond, Cond);
+ Cond = new ICmpInst(Predicate, NewIncV, RHS,
+ L->getHeader()->getName() + ".termcond",
+ OldCond);
// Remove the old compare instruction. The old indvar is probably dead too.
DeadInsts.insert(cast<Instruction>(CondUse->OperandValToReplace));
diff --git a/test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness.ll b/test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness.ll
new file mode 100644
index 0000000..9a54b7b
--- /dev/null
+++ b/test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness.ll
@@ -0,0 +1,20 @@
+; RUN: llvm-as < %s | llc
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
+target triple = "x86_64-apple-darwin9"
+
+define void @foo() {
+entry:
+ br label %loop
+
+loop:
+ %indvar = phi i32 [ 0, %entry ], [ %i.2.0.us1534, %loop ] ; <i32> [#uses=1]
+ %i.2.0.us1534 = add i32 %indvar, 1 ; <i32> [#uses=3]
+ %tmp611.us1535 = icmp eq i32 %i.2.0.us1534, 4 ; <i1> [#uses=2]
+ %tmp623.us1538 = select i1 %tmp611.us1535, i32 6, i32 0 ; <i32> [#uses=0]
+ %tmp628.us1540 = shl i32 %i.2.0.us1534, 1 ; <i32> [#uses=1]
+ %tmp645646647.us1547 = sext i32 %tmp628.us1540 to i64 ; <i64> [#uses=0]
+ br i1 %tmp611.us1535, label %exit, label %loop
+
+exit:
+ ret void
+}