[PATCH] D117995: [ValueTracking] Add support for X*X self-multiplication

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon updated this revision to Diff 406268.
RKSimon added a comment.
This revision is now accepted and ready to land.

Updated with check for undef operand


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D117995/new/

https://reviews.llvm.org/D117995

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Transforms/InstCombine/mul-masked-bits.ll


Index: llvm/test/Transforms/InstCombine/mul-masked-bits.ll
===================================================================
--- llvm/test/Transforms/InstCombine/mul-masked-bits.ll
+++ llvm/test/Transforms/InstCombine/mul-masked-bits.ll
@@ -70,8 +70,7 @@
 ; CHECK-LABEL: @combine_mul_self_demandedbits_vector(
 ; CHECK-NEXT:    [[TMP1:%.*]] = freeze <4 x i32> [[X:%.*]]
 ; CHECK-NEXT:    [[TMP2:%.*]] = mul <4 x i32> [[TMP1]], [[TMP1]]
-; CHECK-NEXT:    [[TMP3:%.*]] = and <4 x i32> [[TMP2]], <i32 -3, i32 -3, i32 -3, i32 -3>
-; CHECK-NEXT:    ret <4 x i32> [[TMP3]]
+; CHECK-NEXT:    ret <4 x i32> [[TMP2]]
 ;
   %1 = freeze <4 x i32> %x
   %2 = mul <4 x i32> %1, %1
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -451,7 +451,11 @@
     }
   }
 
-  Known = KnownBits::mul(Known, Known2);
+  bool SelfMultiply = Op0 == Op1;
+  // TODO: SelfMultiply can be poison, but not undef.
+  SelfMultiply &=
+      isGuaranteedNotToBeUndefOrPoison(Op0, Q.AC, Q.CxtI, Q.DT, Depth + 1);
+  Known = KnownBits::mul(Known, Known2, SelfMultiply);
 
   // Only make use of no-wrap flags if we failed to compute the sign bit
   // directly.  This matters if the multiplication always overflows, in


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