aboutsummaryrefslogtreecommitdiff
path: root/llvm/lib/Analysis/ValueTracking.cpp
diff options
context:
space:
mode:
authorNoah Goldstein <goldstein.w.n@gmail.com>2023-08-24 14:22:05 -0500
committerNoah Goldstein <goldstein.w.n@gmail.com>2023-08-24 19:43:10 -0500
commit846ff921ffe8bf43eb2f66869475ad9a5ef0a02a (patch)
tree69c14e29735360890541553fd39265c136635893 /llvm/lib/Analysis/ValueTracking.cpp
parentd0b4ed9a2cf353eb9f59be344862595af2bd205d (diff)
downloadllvm-846ff921ffe8bf43eb2f66869475ad9a5ef0a02a.zip
llvm-846ff921ffe8bf43eb2f66869475ad9a5ef0a02a.tar.gz
llvm-846ff921ffe8bf43eb2f66869475ad9a5ef0a02a.tar.bz2
[ValueTracking] Compute `sdiv` as non-zero if `abs(num) u>= abs(denum)`
Just covering an additional case. Proof: https://alive2.llvm.org/ce/z/MJz9fT Reviewed By: nikic Differential Revision: https://reviews.llvm.org/D157302
Diffstat (limited to 'llvm/lib/Analysis/ValueTracking.cpp')
-rw-r--r--llvm/lib/Analysis/ValueTracking.cpp37
1 files changed, 22 insertions, 15 deletions
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 54539d2..06162c6 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2570,26 +2570,33 @@ static bool isKnownNonZeroFromOperator(const Operator *I,
return isNonZeroShift(I, DemandedElts, Depth, Q, Known);
}
case Instruction::UDiv:
- case Instruction::SDiv:
+ case Instruction::SDiv: {
// X / Y
// 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) {
- std::optional<bool> XUgeY;
- KnownBits XKnown =
- computeKnownBits(I->getOperand(0), DemandedElts, Depth, Q);
- if (!XKnown.isUnknown()) {
- KnownBits YKnown =
- computeKnownBits(I->getOperand(1), DemandedElts, Depth, Q);
- // If X u>= Y then div is non zero (0/0 is UB).
- XUgeY = KnownBits::uge(XKnown, YKnown);
- }
- // If X is total unknown or X u< Y we won't be able to prove non-zero
- // with compute known bits so just return early.
- return XUgeY && *XUgeY;
+
+ std::optional<bool> XUgeY;
+ KnownBits XKnown =
+ computeKnownBits(I->getOperand(0), DemandedElts, Depth, Q);
+ // If X is fully unknown we won't be able to figure anything out so don't
+ // both computing knownbits for Y.
+ if (XKnown.isUnknown())
+ return false;
+
+ KnownBits YKnown =
+ computeKnownBits(I->getOperand(1), DemandedElts, Depth, Q);
+ if (I->getOpcode() == Instruction::SDiv) {
+ // For signed division need to compare abs value of the operands.
+ XKnown = XKnown.abs(/*IntMinIsPoison*/ false);
+ YKnown = YKnown.abs(/*IntMinIsPoison*/ false);
}
- break;
+ // If X u>= Y then div is non zero (0/0 is UB).
+ XUgeY = KnownBits::uge(XKnown, YKnown);
+ // If X is total unknown or X u< Y we won't be able to prove non-zero
+ // with compute known bits so just return early.
+ return XUgeY && *XUgeY;
+ }
case Instruction::Add: {
// X + Y.