[PATCH] D147898: [ValueTracking] Add `shl nsw %val, %cnt != 0` if `%val != 0`.

[Noah Goldstein via Phabricator via llvm-commits]

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Alive2 Link: https://alive2.llvm.org/ce/z/mxZLJn


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D147898

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Analysis/ValueTracking/known-non-zero.ll


Index: llvm/test/Analysis/ValueTracking/known-non-zero.ll
===================================================================
--- llvm/test/Analysis/ValueTracking/known-non-zero.ll
+++ llvm/test/Analysis/ValueTracking/known-non-zero.ll
@@ -227,9 +227,7 @@
 ; CHECK-LABEL: @shl_non_zero_nsw(
 ; CHECK-NEXT:    [[NZ:%.*]] = icmp ne i8 [[S:%.*]], 0
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[NZ]])
-; CHECK-NEXT:    [[V:%.*]] = shl nsw i8 [[S]], [[CNT:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[V]], 0
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 false
 ;
   %nz = icmp ne i8 %s, 0
   call void @llvm.assume(i1 %nz)
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -2670,9 +2670,9 @@
     return isKnownNonZero(I->getOperand(0), Depth, Q);
 
   case Instruction::Shl: {
-    // shl nuw can't remove any non-zero bits.
+    // shl nsw/nuw can't remove any non-zero bits.
     const OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V);
-    if (Q.IIQ.hasNoUnsignedWrap(BO))
+    if (Q.IIQ.hasNoUnsignedWrap(BO) || Q.IIQ.hasNoSignedWrap(BO))
       return isKnownNonZero(I->getOperand(0), Depth, Q);
 
     // shl X, Y != 0 if X is odd.  Note that the value of the shift is undefined


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