[ValueTracking] Make sure we keep range metadata information when calculating known bits for calls to bitreverse intrinsic.

llvm-svn: 298488

Author: topperc

llvm/lib/Analysis/ValueTracking.cpp

@@ -1414,8 +1414,8 @@ static void computeKnownBitsFromOperator(const Operator *I, APInt &KnownZero,
       default: break;
       case Intrinsic::bitreverse:
         computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1, Q);
-        KnownZero = KnownZero2.reverseBits();
-        KnownOne = KnownOne2.reverseBits();
+        KnownZero |= KnownZero2.reverseBits();
+        KnownOne |= KnownOne2.reverseBits();
         break;
       case Intrinsic::bswap:
         computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1, Q);

llvm/test/Transforms/InstCombine/bitreverse-known-bits.ll

@@ -1,5 +1,6 @@
 ; RUN: opt < %s -S -instcombine | FileCheck %s
 
+declare i8 @llvm.bitreverse.i8(i8)
 declare i32 @llvm.bitreverse.i32(i32)
 
 ; CHECK-LABEL: @test1
@@ -32,3 +33,19 @@ define i1 @test3(i32 %arg) {
   %res = icmp eq i32 %and, 0
   ret i1 %res
 }
+
+; CHECK-LABEL: @add_bitreverse
+; Make sure we process range metadata on bitreverse
+define i8 @add_bitreverse(i8 %a) {
+  %b = and i8 %a, 252
+  ; known bits for the bitreverse will say the result is in the range [0, 64)
+  ; but the metadata says [0, 16). So make sure the range metadata wins.
+  ;    add %reverse, 1111 0000
+  ; should become
+  ;    or  %reverse, 1111 0000
+  %reverse = call i8 @llvm.bitreverse.i8(i8 %b), !range !1
+  %c = add i8 %reverse, -16
+; CHECK: or i8 %reverse, -16
+  ret i8 %c
+}
+!1 = !{i8 0, i8 16}