Switch invars away from using isTrapping when it really shouldn't be

using it.

llvm-svn: 75852

2 files changed, 26 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index 1a6c6a13211..0ac58f1fea9 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -544,7 +544,13 @@ void IndVarSimplify::SinkUnusedInvariants(Loop *L) {
     // New instructions were inserted at the end of the preheader.
     if (isa<PHINode>(I))
       break;
-    if (I->isTrapping())
+    // Don't move instructions which might have side effects, since the side
+    // effects need to complete before instructions inside the loop.  Also
+    // don't move instructions which might read memory, since the loop may
+    // modify memory. Note that it's okay if the instruction might have
+    // undefined behavior: LoopSimplify guarantees that the preheader
+    // dominates the exit block.
+    if (I->mayHaveSideEffects() || I->mayReadFromMemory())
       continue;
     // Determine if there is a use in or before the loop (direct or
     // otherwise).
diff --git a/llvm/test/Transforms/IndVarSimplify/sink-trapping.ll b/llvm/test/Transforms/IndVarSimplify/sink-trapping.ll
new file mode 100644
index 00000000000..5382c92e44a
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/sink-trapping.ll
@@ -0,0 +1,19 @@
+; RUN: llvm-as < %s | opt -indvars | llvm-dis | FileCheck %s --check-prefix=CHECK
+
+declare i1 @b()
+
+define i32 @a(i32 %x) nounwind {
+for.body.preheader:
+    %y = sdiv i32 10, %x
+	br label %for.body
+
+for.body:
+    %cmp = call i1 @b()
+	br i1 %cmp, label %for.body, label %for.end.loopexit
+
+for.end.loopexit:
+	ret i32 %y
+}
+; CHECK: for.end.loopexit:
+; CHECK: sdiv
+; CHECK: ret