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[InstSimplify] Simplify saturating add/sub + icmp

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If a saturating add/sub has one constant operand, then we can
determine the possible range of outputs it can produce, and simplify
an icmp comparison based on that.

The implementation is based on a similar existing mechanism for
simplifying binary operator + icmps.

Differential Revision: https://reviews.llvm.org/D55735

llvm-svn: 349369
This commit is contained in:
Nikita Popov 2018-12-17 17:45:18 +00:00
parent ce9abb7e3a
commit 6d62833353
2 changed files with 80 additions and 42 deletions
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66
lib/Analysis/InstructionSimplify.cpp
View File

@ -2630,6 +2630,70 @@ static void setLimitsForBinOp(BinaryOperator &BO, APInt &Lower, APInt &Upper,
}
}
/// Some intrinsics with a constant operand have an easy-to-compute range of
/// outputs. This can be used to fold a comparison to always true or always
/// false.
static void setLimitsForIntrinsic(IntrinsicInst &II, APInt &Lower,
APInt &Upper) {
unsigned Width = Lower.getBitWidth();
const APInt *C;
switch (II.getIntrinsicID()) {
case Intrinsic::uadd_sat:
// uadd.sat(x, C) produces [C, UINT_MAX].
if (match(II.getOperand(0), m_APInt(C)) ||
match(II.getOperand(1), m_APInt(C)))
Lower = *C;
break;
case Intrinsic::sadd_sat:
if (match(II.getOperand(0), m_APInt(C)) ||
match(II.getOperand(1), m_APInt(C))) {
if (C->isNegative()) {
// sadd.sat(x, -C) produces [SINT_MIN, SINT_MAX + (-C)].
Lower = APInt::getSignedMinValue(Width);
Upper = APInt::getSignedMaxValue(Width) + *C + 1;
} else {
// sadd.sat(x, +C) produces [SINT_MIN + C, SINT_MAX].
Lower = APInt::getSignedMinValue(Width) + *C;
Upper = APInt::getSignedMaxValue(Width) + 1;
}
}
break;
case Intrinsic::usub_sat:
// usub.sat(C, x) produces [0, C].
if (match(II.getOperand(0), m_APInt(C)))
Upper = *C + 1;
// usub.sat(x, C) produces [0, UINT_MAX - C].
else if (match(II.getOperand(1), m_APInt(C)))
Upper = APInt::getMaxValue(Width) - *C + 1;
break;
case Intrinsic::ssub_sat:
if (match(II.getOperand(0), m_APInt(C))) {
if (C->isNegative()) {
// ssub.sat(-C, x) produces [SINT_MIN, -SINT_MIN + (-C)].
Lower = APInt::getSignedMinValue(Width);
Upper = *C - APInt::getSignedMinValue(Width) + 1;
} else {
// ssub.sat(+C, x) produces [-SINT_MAX + C, SINT_MAX].
Lower = *C - APInt::getSignedMaxValue(Width);
Upper = APInt::getSignedMaxValue(Width) + 1;
}
} else if (match(II.getOperand(1), m_APInt(C))) {
if (C->isNegative()) {
// ssub.sat(x, -C) produces [SINT_MIN - (-C), SINT_MAX]:
Lower = APInt::getSignedMinValue(Width) - *C;
Upper = APInt::getSignedMaxValue(Width) + 1;
} else {
// ssub.sat(x, +C) produces [SINT_MIN, SINT_MAX - C].
Lower = APInt::getSignedMinValue(Width);
Upper = APInt::getSignedMaxValue(Width) - *C + 1;
}
}
break;
default:
break;
}
}
static Value *simplifyICmpWithConstant(CmpInst::Predicate Pred, Value *LHS,
Value *RHS, const InstrInfoQuery &IIQ) {
Type *ITy = GetCompareTy(RHS); // The return type.
@ -2663,6 +2727,8 @@ static Value *simplifyICmpWithConstant(CmpInst::Predicate Pred, Value *LHS,
APInt Upper = APInt(Width, 0);
if (auto *BO = dyn_cast<BinaryOperator>(LHS))
setLimitsForBinOp(*BO, Lower, Upper, IIQ);
else if (auto *II = dyn_cast<IntrinsicInst>(LHS))
setLimitsForIntrinsic(*II, Lower, Upper);
ConstantRange LHS_CR =
Lower != Upper ? ConstantRange(Lower, Upper) : ConstantRange(Width, true);

56
test/Transforms/InstSimplify/saturating-add-sub.ll
View File

@ -408,9 +408,7 @@ define <2 x i8> @ssub_vector_same(<2 x i8> %a) {
define i1 @uadd_icmp_op0_known(i8 %a) {
; CHECK-LABEL: @uadd_icmp_op0_known(
; CHECK-NEXT: [[B:%.*]] = call i8 @llvm.uadd.sat.i8(i8 10, i8 [[A:%.*]])
; CHECK-NEXT: [[C:%.*]] = icmp uge i8 [[B]], 10
; CHECK-NEXT: ret i1 [[C]]
; CHECK-NEXT: ret i1 true
;
%b = call i8 @llvm.uadd.sat.i8(i8 10, i8 %a)
%c = icmp uge i8 %b, 10
@ -430,9 +428,7 @@ define i1 @uadd_icmp_op0_unknown(i8 %a) {
define i1 @uadd_icmp_op1_known(i8 %a) {
; CHECK-LABEL: @uadd_icmp_op1_known(
; CHECK-NEXT: [[B:%.*]] = call i8 @llvm.uadd.sat.i8(i8 [[A:%.*]], i8 10)
; CHECK-NEXT: [[C:%.*]] = icmp uge i8 [[B]], 10
; CHECK-NEXT: ret i1 [[C]]
; CHECK-NEXT: ret i1 true
;
%b = call i8 @llvm.uadd.sat.i8(i8 %a, i8 10)
%c = icmp uge i8 %b, 10
@ -452,9 +448,7 @@ define i1 @uadd_icmp_op1_unknown(i8 %a) {
define i1 @sadd_icmp_op0_pos_known(i8 %a) {
; CHECK-LABEL: @sadd_icmp_op0_pos_known(
; CHECK-NEXT: [[B:%.*]] = call i8 @llvm.sadd.sat.i8(i8 10, i8 [[A:%.*]])
; CHECK-NEXT: [[C:%.*]] = icmp sge i8 [[B]], -118
; CHECK-NEXT: ret i1 [[C]]
; CHECK-NEXT: ret i1 true
;
%b = call i8 @llvm.sadd.sat.i8(i8 10, i8 %a)
%c = icmp sge i8 %b, -118
@ -474,9 +468,7 @@ define i1 @sadd_icmp_op0_pos_unknown(i8 %a) {
define i1 @sadd_icmp_op0_neg_known(i8 %a) {
; CHECK-LABEL: @sadd_icmp_op0_neg_known(
; CHECK-NEXT: [[B:%.*]] = call i8 @llvm.sadd.sat.i8(i8 -10, i8 [[A:%.*]])
; CHECK-NEXT: [[C:%.*]] = icmp sle i8 [[B]], 117
; CHECK-NEXT: ret i1 [[C]]
; CHECK-NEXT: ret i1 true
;
%b = call i8 @llvm.sadd.sat.i8(i8 -10, i8 %a)
%c = icmp sle i8 %b, 117
@ -496,9 +488,7 @@ define i1 @sadd_icmp_op0_neg_unknown(i8 %a) {
define i1 @sadd_icmp_op1_pos_known(i8 %a) {
; CHECK-LABEL: @sadd_icmp_op1_pos_known(
; CHECK-NEXT: [[B:%.*]] = call i8 @llvm.sadd.sat.i8(i8 [[A:%.*]], i8 10)
; CHECK-NEXT: [[C:%.*]] = icmp sge i8 [[B]], -118
; CHECK-NEXT: ret i1 [[C]]
; CHECK-NEXT: ret i1 true
;
%b = call i8 @llvm.sadd.sat.i8(i8 %a, i8 10)
%c = icmp sge i8 %b, -118
@ -518,9 +508,7 @@ define i1 @sadd_icmp_op1_pos_unknown(i8 %a) {
define i1 @sadd_icmp_op1_neg_known(i8 %a) {
; CHECK-LABEL: @sadd_icmp_op1_neg_known(
; CHECK-NEXT: [[B:%.*]] = call i8 @llvm.sadd.sat.i8(i8 [[A:%.*]], i8 -10)
; CHECK-NEXT: [[C:%.*]] = icmp sle i8 [[B]], 117
; CHECK-NEXT: ret i1 [[C]]
; CHECK-NEXT: ret i1 true
;
%b = call i8 @llvm.sadd.sat.i8(i8 %a, i8 -10)
%c = icmp sle i8 %b, 117
@ -540,9 +528,7 @@ define i1 @sadd_icmp_op1_neg_unknown(i8 %a) {
define i1 @usub_icmp_op0_known(i8 %a) {
; CHECK-LABEL: @usub_icmp_op0_known(
; CHECK-NEXT: [[B:%.*]] = call i8 @llvm.usub.sat.i8(i8 10, i8 [[A:%.*]])
; CHECK-NEXT: [[C:%.*]] = icmp ule i8 [[B]], 10
; CHECK-NEXT: ret i1 [[C]]
; CHECK-NEXT: ret i1 true
;
%b = call i8 @llvm.usub.sat.i8(i8 10, i8 %a)
%c = icmp ule i8 %b, 10
@ -562,9 +548,7 @@ define i1 @usub_icmp_op0_unknown(i8 %a) {
define i1 @usub_icmp_op1_known(i8 %a) {
; CHECK-LABEL: @usub_icmp_op1_known(
; CHECK-NEXT: [[B:%.*]] = call i8 @llvm.usub.sat.i8(i8 [[A:%.*]], i8 10)
; CHECK-NEXT: [[C:%.*]] = icmp ule i8 [[B]], -11
; CHECK-NEXT: ret i1 [[C]]
; CHECK-NEXT: ret i1 true
;
%b = call i8 @llvm.usub.sat.i8(i8 %a, i8 10)
%c = icmp ule i8 %b, 245
@ -584,9 +568,7 @@ define i1 @usub_icmp_op1_unknown(i8 %a) {
define i1 @ssub_icmp_op0_pos_known(i8 %a) {
; CHECK-LABEL: @ssub_icmp_op0_pos_known(
; CHECK-NEXT: [[B:%.*]] = call i8 @llvm.ssub.sat.i8(i8 10, i8 [[A:%.*]])
; CHECK-NEXT: [[C:%.*]] = icmp sge i8 [[B]], -117
; CHECK-NEXT: ret i1 [[C]]
; CHECK-NEXT: ret i1 true
;
%b = call i8 @llvm.ssub.sat.i8(i8 10, i8 %a)
%c = icmp sge i8 %b, -117
@ -606,9 +588,7 @@ define i1 @ssub_icmp_op0_pos_unknown(i8 %a) {
define i1 @ssub_icmp_op0_neg_known(i8 %a) {
; CHECK-LABEL: @ssub_icmp_op0_neg_known(
; CHECK-NEXT: [[B:%.*]] = call i8 @llvm.ssub.sat.i8(i8 -10, i8 [[A:%.*]])
; CHECK-NEXT: [[C:%.*]] = icmp sle i8 [[B]], 118
; CHECK-NEXT: ret i1 [[C]]
; CHECK-NEXT: ret i1 true
;
%b = call i8 @llvm.ssub.sat.i8(i8 -10, i8 %a)
%c = icmp sle i8 %b, 118
@ -629,9 +609,7 @@ define i1 @ssub_icmp_op0_neg_unknown(i8 %a) {
; Peculiar case: ssub.sat(0, x) is never signed min.
define i1 @ssub_icmp_op0_zero(i8 %a) {
; CHECK-LABEL: @ssub_icmp_op0_zero(
; CHECK-NEXT: [[B:%.*]] = call i8 @llvm.ssub.sat.i8(i8 0, i8 [[A:%.*]])
; CHECK-NEXT: [[C:%.*]] = icmp ne i8 [[B]], -128
; CHECK-NEXT: ret i1 [[C]]
; CHECK-NEXT: ret i1 true
;
%b = call i8 @llvm.ssub.sat.i8(i8 0, i8 %a)
%c = icmp ne i8 %b, -128
@ -640,9 +618,7 @@ define i1 @ssub_icmp_op0_zero(i8 %a) {
define i1 @ssub_icmp_op1_pos_known(i8 %a) {
; CHECK-LABEL: @ssub_icmp_op1_pos_known(
; CHECK-NEXT: [[B:%.*]] = call i8 @llvm.ssub.sat.i8(i8 [[A:%.*]], i8 10)
; CHECK-NEXT: [[C:%.*]] = icmp sle i8 [[B]], 117
; CHECK-NEXT: ret i1 [[C]]
; CHECK-NEXT: ret i1 true
;
%b = call i8 @llvm.ssub.sat.i8(i8 %a, i8 10)
%c = icmp sle i8 %b, 117
@ -662,9 +638,7 @@ define i1 @ssub_icmp_op1_pos_unknown(i8 %a) {
define i1 @ssub_icmp_op1_neg_known(i8 %a) {
; CHECK-LABEL: @ssub_icmp_op1_neg_known(
; CHECK-NEXT: [[B:%.*]] = call i8 @llvm.ssub.sat.i8(i8 [[A:%.*]], i8 -10)
; CHECK-NEXT: [[C:%.*]] = icmp sge i8 [[B]], -118
; CHECK-NEXT: ret i1 [[C]]
; CHECK-NEXT: ret i1 true
;
%b = call i8 @llvm.ssub.sat.i8(i8 %a, i8 -10)
%c = icmp sge i8 %b, -118
@ -684,9 +658,7 @@ define i1 @ssub_icmp_op1_neg_unknown(i8 %a) {
define i1 @ssub_icmp_op1_smin(i8 %a) {
; CHECK-LABEL: @ssub_icmp_op1_smin(
; CHECK-NEXT: [[B:%.*]] = call i8 @llvm.ssub.sat.i8(i8 [[A:%.*]], i8 -128)
; CHECK-NEXT: [[C:%.*]] = icmp sge i8 [[B]], 0
; CHECK-NEXT: ret i1 [[C]]
; CHECK-NEXT: ret i1 true
;
%b = call i8 @llvm.ssub.sat.i8(i8 %a, i8 -128)
%c = icmp sge i8 %b, 0