[Analysis] bitreverse(undef) returns undef

Summary:
The reverse of an artbitrary bitpattern is also an arbitrary
bitpattern.

Reviewers: trentxintong, arsenm, majnemer

Reviewed By: majnemer

Subscribers: majnemer, wdng, llvm-commits

Differential Revision: https://reviews.llvm.org/D31118

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298201 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/ConstantFolding.cpp b/lib/Analysis/ConstantFolding.cpp
index 6d8d4a1c3e90ce3617eed9c7490202305b0c72c2..85ca622a25dc83fe3532d1201efd8fe61cc26205 100644 (file)
--- a/lib/Analysis/ConstantFolding.cpp
+++ b/lib/Analysis/ConstantFolding.cpp
@@ -1768,7 +1768,8 @@ Constant *ConstantFoldScalarCall(StringRef Name, unsigned IntrinsicID, Type *Ty,
     }
 
     if (isa<UndefValue>(Operands[0])) {
-      if (IntrinsicID == Intrinsic::bswap)
+      if (IntrinsicID == Intrinsic::bswap ||
+          IntrinsicID == Intrinsic::bitreverse)
         return Operands[0];
       return nullptr;
     }

diff --git a/test/Transforms/InstCombine/bitreverse-fold.ll b/test/Transforms/InstCombine/bitreverse-fold.ll
index ecdfbc8cb5f995e91f66f8a26543e474bd49977c..b798ad33b3f087548ec5c75ef00731fa77428b89 100644 (file)
--- a/test/Transforms/InstCombine/bitreverse-fold.ll
+++ b/test/Transforms/InstCombine/bitreverse-fold.ll
@@ -37,6 +37,13 @@ define i32 @reverse_neg1_i32() {
   ret i32 %x
 }
 
+; CHECK-LABEL: @reverse_undef_i32(
+; CHECK-NEXT: ret i32 undef
+define i32 @reverse_undef_i32() {
+  %x = call i32 @llvm.bitreverse.i32(i32 undef)
+  ret i32 %x
+}
+
 ; CHECK-LABEL: @reverse_false_i1(
 ; CHECK-NEXT: ret i1 false
 define i1 @reverse_false_i1() {
@@ -51,6 +58,13 @@ define i1 @reverse_true_i1() {
   ret i1 %x
 }
 
+; CHECK-LABEL: @reverse_undef_i1(
+; CHECK-NEXT: ret i1 undef
+define i1 @reverse_undef_i1() {
+  %x = call i1 @llvm.bitreverse.i1(i1 undef)
+  ret i1 %x
+}
+
 ; CHECK-LABEL: @reverse_false_v2i1(
 ; CHECK-NEXT: ret <2 x i1> zeroinitializer
 define <2 x i1> @reverse_false_v2i1() {