[PATCH] D150425: [ValueTracking] deduce `X * Y != 0` if `LowestKnownBit(X) * LowestKnownBit(Y) != 0`
Noah Goldstein via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Fri May 12 15:08:18 PDT 2023
goldstein.w.n updated this revision to Diff 521813.
goldstein.w.n added a comment.
Rebase
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D150425/new/
https://reviews.llvm.org/D150425
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
@@ -1099,11 +1099,7 @@
define i1 @mul_nonzero_contains_nonzero_mul(i8 %x, i8 %y) {
; CHECK-LABEL: @mul_nonzero_contains_nonzero_mul(
-; CHECK-NEXT: [[XX:%.*]] = or i8 [[X:%.*]], 16
-; CHECK-NEXT: [[YY:%.*]] = or i8 [[Y:%.*]], 8
-; CHECK-NEXT: [[XY:%.*]] = mul i8 [[XX]], [[YY]]
-; CHECK-NEXT: [[NZ:%.*]] = icmp ne i8 [[XY]], 0
-; CHECK-NEXT: ret i1 [[NZ]]
+; CHECK-NEXT: ret i1 true
;
%xx = or i8 %x, 16
%yy = or i8 %y, 8
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -2887,6 +2887,17 @@
return XKnown.isNonZero() ||
isKnownNonZero(I->getOperand(0), DemandedElts, Depth, Q);
+ // If there exists any subset of X (sX) and subset of Y (sY) s.t sX * sY is
+ // non-zero, then X * Y is non-zero. We can find sX and sY by just taking
+ // the the lowest known One of X and Y. If they are non-zero, the result
+ // must be non-zero.
+ if (XKnown.isNonZero() && YKnown.isNonZero()) {
+ APInt XLowBit = XKnown.One & (-XKnown.One);
+ APInt YLowBit = YKnown.One & (-YKnown.One);
+ if (!(XLowBit * YLowBit).isZero())
+ return true;
+ }
+
return KnownBits::mul(XKnown, YKnown).isNonZero();
}
case Instruction::Select:
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