InstCombine: Fix infinite loop caused by visitFPTrunc

We would attempt to replace a fptrunc of an frem with an identical
fptrunc.  This would cause the new fptrunc to be added to the worklist.
Of course, this results in an infinite loop because we will keep
visiting the newly created fptruncs.

This fixes PR21576.

llvm-svn: 222040

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/fpcast.ll b/llvm/test/Transforms/InstCombine/fpcast.ll
index 9be66fd42c6..c4c8578198b 100644
--- a/llvm/test/Transforms/InstCombine/fpcast.ll
+++ b/llvm/test/Transforms/InstCombine/fpcast.ll
@@ -53,3 +53,13 @@ define half @test5(float %a, float %b, float %c) {
 }
 
 declare float @llvm.fabs.f32(float) nounwind readonly
+
+define <1 x float> @test6(<1 x double> %V) {
+  %frem = frem <1 x double> %V, %V
+  %trunc = fptrunc <1 x double> %frem to <1 x float>
+  ret <1 x float> %trunc
+; CHECK-LABEL: @test6
+; CHECK-NEXT: %[[frem:.*]]  = frem <1 x double> %V, %V
+; CHECK-NEXT: %[[trunc:.*]] = fptrunc <1 x double> %[[frem]] to <1 x float>
+; CHECK-NEXT: ret <1 x float> %trunc
+}