[llvm] ae9414d - [ValueTracking] Only check for non-undef/poison if already known to be a self-multiply

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2022-02-08T18:35:29+03:00
New Revision: ae9414d5621f6de5060007ee12c3face233a98c1

URL: https://github.com/llvm/llvm-project/commit/ae9414d5621f6de5060007ee12c3face233a98c1
DIFF: https://github.com/llvm/llvm-project/commit/ae9414d5621f6de5060007ee12c3face233a98c1.diff

LOG: [ValueTracking] Only check for non-undef/poison if already known to be a self-multiply

https://godbolt.org/z/js9fTTG9h
^ we don't care what `isGuaranteedNotToBeUndefOrPoison()` says
unless we already knew that the operands were equal.

Added: 
    

Modified: 
    llvm/lib/Analysis/ValueTracking.cpp
    llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 9fe538df1a87..236db5ef26f8 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -453,8 +453,9 @@ static void computeKnownBitsMul(const Value *Op0, const Value *Op1, bool NSW,
 
   bool SelfMultiply = Op0 == Op1;
   // TODO: SelfMultiply can be poison, but not undef.
-  SelfMultiply &=
-      isGuaranteedNotToBeUndefOrPoison(Op0, Q.AC, Q.CxtI, Q.DT, Depth + 1);
+  if (SelfMultiply)
+    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

diff  --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index df09368f6a8a..9693cede668c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -3083,8 +3083,9 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
     Known2 = computeKnownBits(Op.getOperand(0), DemandedElts, Depth + 1);
     bool SelfMultiply = Op.getOperand(0) == Op.getOperand(1);
     // TODO: SelfMultiply can be poison, but not undef.
-    SelfMultiply &= isGuaranteedNotToBeUndefOrPoison(
-        Op.getOperand(0), DemandedElts, false, Depth + 1);
+    if (SelfMultiply)
+      SelfMultiply &= isGuaranteedNotToBeUndefOrPoison(
+          Op.getOperand(0), DemandedElts, false, Depth + 1);
     Known = KnownBits::mul(Known, Known2, SelfMultiply);
     break;
   }