[PATCH] D31118: [Analysis] bitreverse(undef) returns undef

[Brian Gesiak via Phabricator via llvm-commits]

modocache created this revision.
Herald added a subscriber: wdng.

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


https://reviews.llvm.org/D31118

Files:
  lib/Analysis/ConstantFolding.cpp
  test/Transforms/InstCombine/bitreverse-fold.ll


Index: test/Transforms/InstCombine/bitreverse-fold.ll
===================================================================
--- test/Transforms/InstCombine/bitreverse-fold.ll
+++ test/Transforms/InstCombine/bitreverse-fold.ll
@@ -37,6 +37,13 @@
   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 @@
   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() {
Index: lib/Analysis/ConstantFolding.cpp
===================================================================
--- lib/Analysis/ConstantFolding.cpp
+++ lib/Analysis/ConstantFolding.cpp
@@ -1768,7 +1768,8 @@
     }
 
     if (isa<UndefValue>(Operands[0])) {
-      if (IntrinsicID == Intrinsic::bswap)
+      if (IntrinsicID == Intrinsic::bswap ||
+          IntrinsicID == Intrinsic::bitreverse)
         return Operands[0];
       return nullptr;
     }


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