SimplifyCFG: Do not transform PHI to select if doing so would be unsafe

PR16069 is an interesting case where an incoming value to a PHI is a
trap value while also being a 'ConstantExpr'.

We do not consider this case when performing the 'HoistThenElseCodeToIf'
optimization.

Instead, make our modifications more conservative if we detect that we
cannot transform the PHI to a select.

llvm-svn: 183152

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/test/Transforms/SimplifyCFG/PR16069.ll b/llvm/test/Transforms/SimplifyCFG/PR16069.ll
new file mode 100644
index 00000000000..4e9f89660c4
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/PR16069.ll
@@ -0,0 +1,14 @@
+; RUN: opt < %s -simplifycfg -S | FileCheck %s
+
+; CHECK-NOT: select
+@b = extern_weak global i32
+define i32 @foo(i1 %y) {
+  br i1 %y, label %bb1, label %bb2
+bb1:
+  br label %bb3
+bb2:
+  br label %bb3
+bb3:
+  %cond.i = phi i32 [ 0, %bb1 ], [ srem (i32 1, i32 zext (i1 icmp eq (i32* @b, i32* null) to i32)), %bb2 ]
+  ret i32 %cond.i
+}