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[InstCombine] Improve eq/ne by parts to handle ult/ugt equality pattern.

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(icmp eq/ne (lshr x, C), (lshr y, C) gets optimized to `(icmp
ult/uge (xor x, y), (1 << C)`. This can cause the current equal by
parts detection to miss the high-bits as it may get optimized to the
new pattern.

This commit adds support for detecting / combining the ult/ugt
pattern.

Closes #69884
This commit is contained in:
Noah Goldstein 2023-10-22 01:19:53 -05:00
parent 9fea6bbf26
commit ad9147399f
2 changed files with 35 additions and 18 deletions
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39
llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
View File

@ -1146,13 +1146,40 @@ Value *InstCombinerImpl::foldEqOfParts(ICmpInst *Cmp0, ICmpInst *Cmp1,
return nullptr;
CmpInst::Predicate Pred = IsAnd ? CmpInst::ICMP_EQ : CmpInst::ICMP_NE;
if (Cmp0->getPredicate() != Pred || Cmp1->getPredicate() != Pred)
return nullptr;
auto GetMatchPart = [&](ICmpInst *Cmp,
unsigned OpNo) -> std::optional<IntPart> {
if (Pred == Cmp->getPredicate())
return matchIntPart(Cmp->getOperand(OpNo));
std::optional<IntPart> L0 = matchIntPart(Cmp0->getOperand(0));
std::optional<IntPart> R0 = matchIntPart(Cmp0->getOperand(1));
std::optional<IntPart> L1 = matchIntPart(Cmp1->getOperand(0));
std::optional<IntPart> R1 = matchIntPart(Cmp1->getOperand(1));
const APInt *C;
// (icmp eq (lshr x, C), (lshr y, C)) gets optimized to:
// (icmp ult (xor x, y), 1 << C) so also look for that.
if (Pred == CmpInst::ICMP_EQ && Cmp->getPredicate() == CmpInst::ICMP_ULT) {
if (!match(Cmp->getOperand(1), m_Power2(C)) ||
!match(Cmp->getOperand(0), m_Xor(m_Value(), m_Value())))
return std::nullopt;
}
// (icmp ne (lshr x, C), (lshr y, C)) gets optimized to:
// (icmp ugt (xor x, y), (1 << C) - 1) so also look for that.
else if (Pred == CmpInst::ICMP_NE &&
Cmp->getPredicate() == CmpInst::ICMP_UGT) {
if (!match(Cmp->getOperand(1), m_LowBitMask(C)) ||
!match(Cmp->getOperand(0), m_Xor(m_Value(), m_Value())))
return std::nullopt;
} else {
return std::nullopt;
}
unsigned From = Pred == CmpInst::ICMP_NE ? C->popcount() : C->countr_zero();
Instruction *I = cast<Instruction>(Cmp->getOperand(0));
return {{I->getOperand(OpNo), From, C->getBitWidth() - From}};
};
std::optional<IntPart> L0 = GetMatchPart(Cmp0, 0);
std::optional<IntPart> R0 = GetMatchPart(Cmp0, 1);
std::optional<IntPart> L1 = GetMatchPart(Cmp1, 0);
std::optional<IntPart> R1 = GetMatchPart(Cmp1, 1);
if (!L0 || !R0 || !L1 || !R1)
return nullptr;

14
llvm/test/Transforms/InstCombine/eq-of-parts.ll
View File

@ -1336,12 +1336,7 @@ define i1 @ne_21_wrong_pred2(i32 %x, i32 %y) {
define i1 @eq_optimized_highbits_cmp(i32 %x, i32 %y) {
; CHECK-LABEL: @eq_optimized_highbits_cmp(
; CHECK-NEXT: [[XOR:%.*]] = xor i32 [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: [[CMP_HI:%.*]] = icmp ult i32 [[XOR]], 33554432
; CHECK-NEXT: [[TX:%.*]] = trunc i32 [[X]] to i25
; CHECK-NEXT: [[TY:%.*]] = trunc i32 [[Y]] to i25
; CHECK-NEXT: [[CMP_LO:%.*]] = icmp eq i25 [[TX]], [[TY]]
; CHECK-NEXT: [[R:%.*]] = and i1 [[CMP_HI]], [[CMP_LO]]
; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[R]]
;
%xor = xor i32 %y, %x
@ -1393,12 +1388,7 @@ define i1 @eq_optimized_highbits_cmp_fail_not_pow2(i32 %x, i32 %y) {
define i1 @ne_optimized_highbits_cmp(i32 %x, i32 %y) {
; CHECK-LABEL: @ne_optimized_highbits_cmp(
; CHECK-NEXT: [[XOR:%.*]] = xor i32 [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: [[CMP_HI:%.*]] = icmp ugt i32 [[XOR]], 16777215
; CHECK-NEXT: [[TX:%.*]] = trunc i32 [[X]] to i24
; CHECK-NEXT: [[TY:%.*]] = trunc i32 [[Y]] to i24
; CHECK-NEXT: [[CMP_LO:%.*]] = icmp ne i24 [[TX]], [[TY]]
; CHECK-NEXT: [[R:%.*]] = or i1 [[CMP_HI]], [[CMP_LO]]
; CHECK-NEXT: [[R:%.*]] = icmp ne i32 [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[R]]
;
%xor = xor i32 %y, %x