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[ValueTracking] Use assume to compute overflowResult. #121665

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[ValueTracking] Use assume to compute overflowResult. #121665

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61157d1
[ValueTracking] add test for use of assume to compute overflowResult.…
andjo403 Jan 4, 2025
8acbe83
[ValueTracking] Use assume to compute overflowResult.
andjo403 Jan 4, 2025
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41 changes: 41 additions & 0 deletions llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7177,10 +7177,33 @@ llvm::computeConstantRangeIncludingKnownBits(const WithCache<const Value *> &V,
return CR1.intersectWith(CR2, RangeType);
}

static bool isKnownToNotOverflowFromAssume(const SimplifyQuery &Q) {
// Use of assumptions is context-sensitive. If we don't have a context, we
// cannot use them!
if (!Q.AC || !Q.CxtI)
return false;

for (AssumptionCache::ResultElem &Elem : Q.AC->assumptionsFor(Q.CxtI)) {
if (!Elem.Assume)
continue;

AssumeInst *I = cast<AssumeInst>(Elem.Assume);
if (match(I->getArgOperand(0),
m_Not(m_ExtractValue<1>(m_Specific(Q.CxtI)))) &&
isValidAssumeForContext(I, Q.CxtI, /*DT=*/nullptr,
/*AllowEphemerals=*/true))
return true;
}
return false;
}

OverflowResult llvm::computeOverflowForUnsignedMul(const Value *LHS,
const Value *RHS,
const SimplifyQuery &SQ,
bool IsNSW) {
if (isKnownToNotOverflowFromAssume(SQ))
return OverflowResult::NeverOverflows;

KnownBits LHSKnown = computeKnownBits(LHS, /*Depth=*/0, SQ);
KnownBits RHSKnown = computeKnownBits(RHS, /*Depth=*/0, SQ);

Expand All @@ -7196,6 +7219,9 @@ OverflowResult llvm::computeOverflowForUnsignedMul(const Value *LHS,
OverflowResult llvm::computeOverflowForSignedMul(const Value *LHS,
const Value *RHS,
const SimplifyQuery &SQ) {
if (isKnownToNotOverflowFromAssume(SQ))
return OverflowResult::NeverOverflows;

// Multiplying n * m significant bits yields a result of n + m significant
// bits. If the total number of significant bits does not exceed the
// result bit width (minus 1), there is no overflow.
Expand Down Expand Up @@ -7236,6 +7262,9 @@ OverflowResult
llvm::computeOverflowForUnsignedAdd(const WithCache<const Value *> &LHS,
const WithCache<const Value *> &RHS,
const SimplifyQuery &SQ) {
if (isKnownToNotOverflowFromAssume(SQ))
return OverflowResult::NeverOverflows;

ConstantRange LHSRange =
computeConstantRangeIncludingKnownBits(LHS, /*ForSigned=*/false, SQ);
ConstantRange RHSRange =
Expand All @@ -7251,6 +7280,9 @@ computeOverflowForSignedAdd(const WithCache<const Value *> &LHS,
return OverflowResult::NeverOverflows;
}

if (isKnownToNotOverflowFromAssume(SQ))
return OverflowResult::NeverOverflows;

// If LHS and RHS each have at least two sign bits, the addition will look
// like
//
Expand Down Expand Up @@ -7305,6 +7337,9 @@ computeOverflowForSignedAdd(const WithCache<const Value *> &LHS,
OverflowResult llvm::computeOverflowForUnsignedSub(const Value *LHS,
const Value *RHS,
const SimplifyQuery &SQ) {
if (isKnownToNotOverflowFromAssume(SQ))
return OverflowResult::NeverOverflows;

// X - (X % ?)
// The remainder of a value can't have greater magnitude than itself,
// so the subtraction can't overflow.
Expand Down Expand Up @@ -7338,6 +7373,9 @@ OverflowResult llvm::computeOverflowForUnsignedSub(const Value *LHS,
OverflowResult llvm::computeOverflowForSignedSub(const Value *LHS,
const Value *RHS,
const SimplifyQuery &SQ) {
if (isKnownToNotOverflowFromAssume(SQ))
return OverflowResult::NeverOverflows;

// X - (X % ?)
// The remainder of a value can't have greater magnitude than itself,
// so the subtraction can't overflow.
Expand Down Expand Up @@ -10180,6 +10218,9 @@ void llvm::findValuesAffectedByCondition(
m_Value()))) {
// Handle patterns that computeKnownFPClass() support.
AddAffected(A);
} else if (IsAssume && match(V, m_Not(m_ExtractValue<1>(m_Value(A)))) &&
isa<WithOverflowInst>(A)) {
AddAffected(A);
}
}
}
129 changes: 129 additions & 0 deletions llvm/test/Transforms/InstCombine/with_overflow.ll
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Expand Up @@ -1064,3 +1064,132 @@ define i8 @smul_7(i8 %x, ptr %p) {
store i1 %ov, ptr %p
ret i8 %r
}

define i8 @uadd_assume_no_overflow(i8 noundef %a, i8 noundef %b) {
; CHECK-LABEL: @uadd_assume_no_overflow(
; CHECK-NEXT: [[CALL:%.*]] = add nuw i8 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: ret i8 [[CALL]]
;
%call = call { i8, i1 } @llvm.uadd.with.overflow.i8(i8 %a, i8 %b)
%overflow = extractvalue { i8, i1 } %call, 1
%ret = extractvalue { i8, i1 } %call, 0
%not = xor i1 %overflow, true
call void @llvm.assume(i1 %not)
ret i8 %ret
}

define i8 @sadd_assume_no_overflow(i8 noundef %a, i8 noundef %b) {
; CHECK-LABEL: @sadd_assume_no_overflow(
; CHECK-NEXT: [[CALL:%.*]] = add nsw i8 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: ret i8 [[CALL]]
;
%call = call { i8, i1 } @llvm.sadd.with.overflow.i8(i8 %a, i8 %b)
%overflow = extractvalue { i8, i1 } %call, 1
%ret = extractvalue { i8, i1 } %call, 0
%not = xor i1 %overflow, true
call void @llvm.assume(i1 %not)
ret i8 %ret
}

define i8 @usub_assume_no_overflow(i8 noundef %a, i8 noundef %b) {
; CHECK-LABEL: @usub_assume_no_overflow(
; CHECK-NEXT: [[CALL:%.*]] = sub nuw i8 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: ret i8 [[CALL]]
;
%call = call { i8, i1 } @llvm.usub.with.overflow.i8(i8 %a, i8 %b)
%overflow = extractvalue { i8, i1 } %call, 1
%ret = extractvalue { i8, i1 } %call, 0
%not = xor i1 %overflow, true
call void @llvm.assume(i1 %not)
ret i8 %ret
}

define i8 @ssub_assume_no_overflow(i8 noundef %a, i8 noundef %b) {
; CHECK-LABEL: @ssub_assume_no_overflow(
; CHECK-NEXT: [[CALL:%.*]] = sub nsw i8 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: ret i8 [[CALL]]
;
%call = call { i8, i1 } @llvm.ssub.with.overflow.i8(i8 %a, i8 %b)
%overflow = extractvalue { i8, i1 } %call, 1
%ret = extractvalue { i8, i1 } %call, 0
%not = xor i1 %overflow, true
call void @llvm.assume(i1 %not)
ret i8 %ret
}

define i8 @umul_assume_no_overflow(i8 noundef %a, i8 noundef %b) {
; CHECK-LABEL: @umul_assume_no_overflow(
; CHECK-NEXT: [[CALL:%.*]] = mul nuw i8 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: ret i8 [[CALL]]
;
%call = call { i8, i1 } @llvm.umul.with.overflow.i8(i8 %a, i8 %b)
%overflow = extractvalue { i8, i1 } %call, 1
%ret = extractvalue { i8, i1 } %call, 0
%not = xor i1 %overflow, true
call void @llvm.assume(i1 %not)
ret i8 %ret
}

define i8 @smul_assume_no_overflow(i8 noundef %a, i8 noundef %b) {
; CHECK-LABEL: @smul_assume_no_overflow(
; CHECK-NEXT: [[CALL:%.*]] = mul nsw i8 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: ret i8 [[CALL]]
;
%call = call { i8, i1 } @llvm.smul.with.overflow.i8(i8 %a, i8 %b)
%overflow = extractvalue { i8, i1 } %call, 1
%ret = extractvalue { i8, i1 } %call, 0
%not = xor i1 %overflow, true
call void @llvm.assume(i1 %not)
ret i8 %ret
}

define i1 @ephemeral_call_assume_no_overflow(i8 noundef %a, i8 noundef %b) {
; CHECK-LABEL: @ephemeral_call_assume_no_overflow(
; CHECK-NEXT: ret i1 true
;
%call = call { i8, i1 } @llvm.smul.with.overflow.i8(i8 %a, i8 %b)
%overflow = extractvalue { i8, i1 } %call, 1
%not = xor i1 %overflow, true
call void @llvm.assume(i1 %not)
ret i1 %not
}

define i8 @neg_assume_overflow(i8 noundef %a, i8 noundef %b) {
; CHECK-LABEL: @neg_assume_overflow(
; CHECK-NEXT: [[CALL:%.*]] = call { i8, i1 } @llvm.smul.with.overflow.i8(i8 [[A:%.*]], i8 [[B:%.*]])
; CHECK-NEXT: [[OVERFLOW:%.*]] = extractvalue { i8, i1 } [[CALL]], 1
; CHECK-NEXT: [[RET:%.*]] = extractvalue { i8, i1 } [[CALL]], 0
; CHECK-NEXT: call void @llvm.assume(i1 [[OVERFLOW]])
; CHECK-NEXT: ret i8 [[RET]]
;
%call = call { i8, i1 } @llvm.smul.with.overflow.i8(i8 %a, i8 %b)
%overflow = extractvalue { i8, i1 } %call, 1
%ret = extractvalue { i8, i1 } %call, 0
call void @llvm.assume(i1 %overflow)
ret i8 %ret
}

define i8 @neg_assume_not_guaranteed_to_execute(i8 noundef %a, i8 noundef %b, i1 %cond) {
; CHECK-LABEL: @neg_assume_not_guaranteed_to_execute(
; CHECK-NEXT: [[CALL:%.*]] = call { i8, i1 } @llvm.smul.with.overflow.i8(i8 [[A:%.*]], i8 [[B:%.*]])
; CHECK-NEXT: br i1 [[COND:%.*]], label [[BB1:%.*]], label [[BB2:%.*]]
; CHECK: bb1:
; CHECK-NEXT: [[OVERFLOW:%.*]] = extractvalue { i8, i1 } [[CALL]], 1
; CHECK-NEXT: [[NOT:%.*]] = xor i1 [[OVERFLOW]], true
; CHECK-NEXT: call void @llvm.assume(i1 [[NOT]])
; CHECK-NEXT: br label [[BB2]]
; CHECK: bb2:
; CHECK-NEXT: [[RET:%.*]] = extractvalue { i8, i1 } [[CALL]], 0
; CHECK-NEXT: ret i8 [[RET]]
;
%call = call { i8, i1 } @llvm.smul.with.overflow.i8(i8 %a, i8 %b)
%overflow = extractvalue { i8, i1 } %call, 1
%ret = extractvalue { i8, i1 } %call, 0
br i1 %cond, label %bb1, label %bb2
bb1:
%not = xor i1 %overflow, true
call void @llvm.assume(i1 %not)
br label %bb2
bb2:
ret i8 %ret
}
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