[PATCH] D149204: [ValueTracking] Add logic for `add nuw x, y != 0` -> `x != 0 || y != 0`

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n created this revision.
goldstein.w.n added reviewers: nikic, spatel, StephenFan.
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goldstein.w.n requested review of this revision.
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Alive2 Link:

  https://alive2.llvm.org/ce/z/TKpqxc


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D149204

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
@@ -473,9 +473,7 @@
 ; CHECK-LABEL: @add_nonzero_nuw(
 ; CHECK-NEXT:    [[X_NZ:%.*]] = icmp ne i8 [[X:%.*]], 0
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[X_NZ]])
-; CHECK-NEXT:    [[A:%.*]] = add nuw i8 [[X]], [[Y:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[A]], 0
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 false
 ;
   %x_nz = icmp ne i8 %x, 0
   call void @llvm.assume(i1 %x_nz)
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -2783,6 +2783,15 @@
     break;
   case Instruction::Add: {
     // X + Y.
+
+    // If Add has nuw wrap flag, then if either X or Y is non-zero the result is
+    // non-zero.
+    auto *BO = cast<OverflowingBinaryOperator>(V);
+    if (Q.IIQ.hasNoUnsignedWrap(BO))
+      if (isKnownNonZero(I->getOperand(0), DemandedElts, Depth, Q) ||
+          isKnownNonZero(I->getOperand(1), DemandedElts, Depth, Q))
+        return true;
+
     KnownBits XKnown =
         computeKnownBits(I->getOperand(0), DemandedElts, Depth, Q);
     KnownBits YKnown =


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