[PATCH] D149203: [ValueTracking] Add logic for `udiv x, y != 0` iff `y u<= x` -> `x != 0`
Noah Goldstein via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Apr 25 15:03:57 PDT 2023
goldstein.w.n updated this revision to Diff 516938.
goldstein.w.n added a comment.
Rebase
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D149203/new/
https://reviews.llvm.org/D149203
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
@@ -501,12 +501,7 @@
define i1 @udiv_y_le_x(i8 %xx, i8 %yy, i8 %z) {
; CHECK-LABEL: @udiv_y_le_x(
-; CHECK-NEXT: [[X:%.*]] = or i8 [[XX:%.*]], 7
-; CHECK-NEXT: [[Y:%.*]] = and i8 [[YY:%.*]], 7
-; CHECK-NEXT: [[D:%.*]] = udiv i8 [[X]], [[Y]]
-; CHECK-NEXT: [[O:%.*]] = or i8 [[D]], [[Z:%.*]]
-; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[O]], 0
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: ret i1 false
;
%x = or i8 %xx, 7
%y = and i8 %yy, 7
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -2769,6 +2769,17 @@
// div exact can only produce a zero if the dividend is zero.
if (cast<PossiblyExactOperator>(I)->isExact())
return isKnownNonZero(I->getOperand(0), DemandedElts, Depth, Q);
+ if (I->getOpcode() == Instruction::UDiv) {
+ KnownBits XKnown =
+ computeKnownBits(I->getOperand(0), DemandedElts, Depth, Q);
+ KnownBits YKnown =
+ computeKnownBits(I->getOperand(1), DemandedElts, Depth, Q);
+ std::optional<bool> YUleX = KnownBits::ule(YKnown, XKnown);
+
+ // If Y u<= X then div is only zero if X is zero.
+ if (YUleX && *YUleX)
+ return isKnownNonZero(I->getOperand(0), DemandedElts, Depth, Q);
+ }
break;
case Instruction::Add: {
// X + Y.
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