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[InstCombine] reduce compare of signbits of 2 values

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Test if 2 values have different or same signbits:
(X u>> BitWidth - 1) == zext (Y s> -1) --> (X ^ Y) < 0
(X u>> BitWidth - 1) != zext (Y s> -1) --> (X ^ Y) > -1

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

As noted in #60242, these patterns regressed between the
14.0 and 15.0 releases - probably due to a change in
canonicalization of related patterns.

The related patterns for testing if 2 values are both
pos/neg appear to be handled already.
This commit is contained in:
Sanjay Patel
2023-01-24 08:11:19 -05:00
parent d1511ed8d1
commit 7cbfc39c77
2 changed files with 47 additions and 25 deletions
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32
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@@ -4653,14 +4653,30 @@ Instruction *InstCombinerImpl::foldICmpEquality(ICmpInst &I) {
}
}
// (B & (Pow2C-1)) == zext A --> A == trunc B
// (B & (Pow2C-1)) != zext A --> A != trunc B
const APInt *MaskC;
if (match(Op0, m_And(m_Value(B), m_LowBitMask(MaskC))) &&
match(Op1, m_ZExt(m_Value(A))) &&
MaskC->countTrailingOnes() == A->getType()->getScalarSizeInBits() &&
(Op0->hasOneUse() || Op1->hasOneUse()))
return new ICmpInst(Pred, A, Builder.CreateTrunc(B, A->getType()));
if (match(Op1, m_ZExt(m_Value(A))) &&
(Op0->hasOneUse() || Op1->hasOneUse())) {
// (B & (Pow2C-1)) == zext A --> A == trunc B
// (B & (Pow2C-1)) != zext A --> A != trunc B
const APInt *MaskC;
if (match(Op0, m_And(m_Value(B), m_LowBitMask(MaskC))) &&
MaskC->countTrailingOnes() == A->getType()->getScalarSizeInBits())
return new ICmpInst(Pred, A, Builder.CreateTrunc(B, A->getType()));
// Test if 2 values have different or same signbits:
// (X u>> BitWidth - 1) == zext (Y s> -1) --> (X ^ Y) < 0
// (X u>> BitWidth - 1) != zext (Y s> -1) --> (X ^ Y) > -1
unsigned OpWidth = Op0->getType()->getScalarSizeInBits();
Value *X, *Y;
ICmpInst::Predicate Pred2;
if (match(Op0, m_LShr(m_Value(X), m_SpecificIntAllowUndef(OpWidth - 1))) &&
match(A, m_ICmp(Pred2, m_Value(Y), m_AllOnes())) &&
Pred2 == ICmpInst::ICMP_SGT && X->getType() == Y->getType()) {
Value *Xor = Builder.CreateXor(X, Y, "xor.signbits");
Value *R = (Pred == ICmpInst::ICMP_EQ) ? Builder.CreateIsNeg(Xor) :
Builder.CreateIsNotNeg(Xor);
return replaceInstUsesWith(I, R);
}
}
// (A >> C) == (B >> C) --> (A^B) u< (1 << C)
// For lshr and ashr pairs.

40
llvm/test/Transforms/InstCombine/icmp-shr.ll
View File

@@ -1302,10 +1302,8 @@ define i1 @lshr_neg_sgt_zero(i8 %x) {
define i1 @exactly_one_set_signbit(i8 %x, i8 %y) {
; CHECK-LABEL: @exactly_one_set_signbit(
; CHECK-NEXT: [[XSIGN:%.*]] = lshr i8 [[X:%.*]], 7
; CHECK-NEXT: [[YPOS:%.*]] = icmp sgt i8 [[Y:%.*]], -1
; CHECK-NEXT: [[YPOSZ:%.*]] = zext i1 [[YPOS]] to i8
; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[XSIGN]], [[YPOSZ]]
; CHECK-NEXT: [[XOR_SIGNBITS:%.*]] = xor i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = icmp slt i8 [[XOR_SIGNBITS]], 0
; CHECK-NEXT: ret i1 [[R]]
;
%xsign = lshr i8 %x, 7
@@ -1319,9 +1317,8 @@ define i1 @exactly_one_set_signbit_use1(i8 %x, i8 %y) {
; CHECK-LABEL: @exactly_one_set_signbit_use1(
; CHECK-NEXT: [[XSIGN:%.*]] = lshr i8 [[X:%.*]], 7
; CHECK-NEXT: call void @use(i8 [[XSIGN]])
; CHECK-NEXT: [[YPOS:%.*]] = icmp sgt i8 [[Y:%.*]], -1
; CHECK-NEXT: [[YPOSZ:%.*]] = zext i1 [[YPOS]] to i8
; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[XSIGN]], [[YPOSZ]]
; CHECK-NEXT: [[XOR_SIGNBITS:%.*]] = xor i8 [[X]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = icmp slt i8 [[XOR_SIGNBITS]], 0
; CHECK-NEXT: ret i1 [[R]]
;
%xsign = lshr i8 %x, 7
@@ -1334,10 +1331,8 @@ define i1 @exactly_one_set_signbit_use1(i8 %x, i8 %y) {
define <2 x i1> @same_signbit(<2 x i8> %x, <2 x i8> %y) {
; CHECK-LABEL: @same_signbit(
; CHECK-NEXT: [[XSIGN:%.*]] = lshr <2 x i8> [[X:%.*]], <i8 7, i8 7>
; CHECK-NEXT: [[YPOS:%.*]] = icmp sgt <2 x i8> [[Y:%.*]], <i8 -1, i8 -1>
; CHECK-NEXT: [[YPOSZ:%.*]] = zext <2 x i1> [[YPOS]] to <2 x i8>
; CHECK-NEXT: [[R:%.*]] = icmp ne <2 x i8> [[XSIGN]], [[YPOSZ]]
; CHECK-NEXT: [[XOR_SIGNBITS:%.*]] = xor <2 x i8> [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = icmp sgt <2 x i8> [[XOR_SIGNBITS]], <i8 -1, i8 -1>
; CHECK-NEXT: ret <2 x i1> [[R]]
;
%xsign = lshr <2 x i8> %x, <i8 7, i8 7>
@@ -1349,11 +1344,11 @@ define <2 x i1> @same_signbit(<2 x i8> %x, <2 x i8> %y) {
define i1 @same_signbit_use2(i8 %x, i8 %y) {
; CHECK-LABEL: @same_signbit_use2(
; CHECK-NEXT: [[XSIGN:%.*]] = lshr i8 [[X:%.*]], 7
; CHECK-NEXT: [[YPOS:%.*]] = icmp sgt i8 [[Y:%.*]], -1
; CHECK-NEXT: [[YPOSZ:%.*]] = zext i1 [[YPOS]] to i8
; CHECK-NEXT: call void @use(i8 [[YPOSZ]])
; CHECK-NEXT: [[R:%.*]] = icmp ne i8 [[XSIGN]], [[YPOSZ]]
; CHECK-NEXT: [[XOR_SIGNBITS:%.*]] = xor i8 [[X:%.*]], [[Y]]
; CHECK-NEXT: [[R:%.*]] = icmp sgt i8 [[XOR_SIGNBITS]], -1
; CHECK-NEXT: ret i1 [[R]]
;
%xsign = lshr i8 %x, 7
@@ -1364,6 +1359,8 @@ define i1 @same_signbit_use2(i8 %x, i8 %y) {
ret i1 %r
}
; negative test
define i1 @same_signbit_use3(i8 %x, i8 %y) {
; CHECK-LABEL: @same_signbit_use3(
; CHECK-NEXT: [[XSIGN:%.*]] = lshr i8 [[X:%.*]], 7
@@ -1385,10 +1382,8 @@ define i1 @same_signbit_use3(i8 %x, i8 %y) {
define <2 x i1> @same_signbit_poison_elts(<2 x i8> %x, <2 x i8> %y) {
; CHECK-LABEL: @same_signbit_poison_elts(
; CHECK-NEXT: [[XSIGN:%.*]] = lshr <2 x i8> [[X:%.*]], <i8 7, i8 poison>
; CHECK-NEXT: [[YPOS:%.*]] = icmp sgt <2 x i8> [[Y:%.*]], <i8 -1, i8 poison>
; CHECK-NEXT: [[YPOSZ:%.*]] = zext <2 x i1> [[YPOS]] to <2 x i8>
; CHECK-NEXT: [[R:%.*]] = icmp ne <2 x i8> [[XSIGN]], [[YPOSZ]]
; CHECK-NEXT: [[XOR_SIGNBITS:%.*]] = xor <2 x i8> [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = icmp sgt <2 x i8> [[XOR_SIGNBITS]], <i8 -1, i8 -1>
; CHECK-NEXT: ret <2 x i1> [[R]]
;
%xsign = lshr <2 x i8> %x, <i8 7, i8 poison>
@@ -1398,6 +1393,8 @@ define <2 x i1> @same_signbit_poison_elts(<2 x i8> %x, <2 x i8> %y) {
ret <2 x i1> %r
}
; negative test
define i1 @same_signbit_wrong_type(i8 %x, i32 %y) {
; CHECK-LABEL: @same_signbit_wrong_type(
; CHECK-NEXT: [[XSIGN:%.*]] = lshr i8 [[X:%.*]], 7
@@ -1412,6 +1409,9 @@ define i1 @same_signbit_wrong_type(i8 %x, i32 %y) {
%r = icmp ne i8 %xsign, %yposz
ret i1 %r
}
; negative test
define i1 @exactly_one_set_signbit_wrong_shamt(i8 %x, i8 %y) {
; CHECK-LABEL: @exactly_one_set_signbit_wrong_shamt(
; CHECK-NEXT: [[XSIGN:%.*]] = lshr i8 [[X:%.*]], 6
@@ -1427,6 +1427,9 @@ define i1 @exactly_one_set_signbit_wrong_shamt(i8 %x, i8 %y) {
ret i1 %r
}
; negative test
; TODO: This could reduce.
define i1 @exactly_one_set_signbit_wrong_shr(i8 %x, i8 %y) {
; CHECK-LABEL: @exactly_one_set_signbit_wrong_shr(
; CHECK-NEXT: [[XSIGN:%.*]] = ashr i8 [[X:%.*]], 7
@@ -1442,6 +1445,9 @@ define i1 @exactly_one_set_signbit_wrong_shr(i8 %x, i8 %y) {
ret i1 %r
}
; negative test
; TODO: This could reduce.
define i1 @exactly_one_set_signbit_wrong_pred(i8 %x, i8 %y) {
; CHECK-LABEL: @exactly_one_set_signbit_wrong_pred(
; CHECK-NEXT: [[XSIGN:%.*]] = lshr i8 [[X:%.*]], 7