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[ValueTracking] Infer is-power-of-2 from assumptions. #107745

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merged 2 commits into from
Sep 10, 2024
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[ValueTracking] Infer is-power-of-2 from assumptions. #107745

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638fdb7
[ValueTracking] Add pre-commit tests. NFC.
dtcxzyw Sep 9, 2024
dc99b69
[ValueTracking] Infer is-power-of-2 from assumptions.
dtcxzyw Sep 9, 2024
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39 changes: 36 additions & 3 deletions llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -613,7 +613,7 @@ static bool isKnownNonZeroFromAssume(const Value *V, const SimplifyQuery &Q) {
CmpInst::Predicate Pred;
auto m_V = m_CombineOr(m_Specific(V), m_PtrToInt(m_Specific(V)));
if (!match(I->getArgOperand(0), m_c_ICmp(Pred, m_V, m_Value(RHS))))
return false;
continue;

if (cmpExcludesZero(Pred, RHS) && isValidAssumeForContext(I, Q.CxtI, Q.DT))
return true;
Expand Down Expand Up @@ -2207,6 +2207,22 @@ static bool isPowerOfTwoRecurrence(const PHINode *PN, bool OrZero,
}
}

/// Return true if we can infer that \p V is known to be a power of 2 from
/// dominating condition \p Cond (e.g., ctpop(V) == 1).
static bool isImpliedToBeAPowerOfTwoFromCond(const Value *V, bool OrZero,
const Value *Cond) {
ICmpInst::Predicate Pred;
const APInt *RHSC;
if (!match(Cond, m_ICmp(Pred, m_Intrinsic<Intrinsic::ctpop>(m_Specific(V)),
m_APInt(RHSC))))
return false;
// ctpop(V) u< 2
if (OrZero && Pred == ICmpInst::ICMP_ULT && *RHSC == 2)
return true;
// ctpop(V) == 1
return Pred == ICmpInst::ICMP_EQ && *RHSC == 1;
}

/// Return true if the given value is known to have exactly one
/// bit set when defined. For vectors return true if every element is known to
/// be a power of two when defined. Supports values with integer or pointer
Expand All @@ -2222,6 +2238,18 @@ bool isKnownToBeAPowerOfTwo(const Value *V, bool OrZero, unsigned Depth,
if (OrZero && V->getType()->getScalarSizeInBits() == 1)
return true;

// Try to infer from assumptions.
if (Q.AC && Q.CxtI) {
for (auto &AssumeVH : Q.AC->assumptionsFor(V)) {
if (!AssumeVH)
continue;
CallInst *I = cast<CallInst>(AssumeVH);
if (isImpliedToBeAPowerOfTwoFromCond(V, OrZero, I->getArgOperand(0)) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT))
return true;
}
}

auto *I = dyn_cast<Instruction>(V);
if (!I)
return false;
Expand Down Expand Up @@ -9903,8 +9931,9 @@ void llvm::findValuesAffectedByCondition(
} else if (match(V, m_ICmp(Pred, m_Value(A), m_Value(B)))) {
AddCmpOperands(A, B);

bool HasRHSC = match(B, m_ConstantInt());
if (ICmpInst::isEquality(Pred)) {
if (match(B, m_ConstantInt())) {
if (HasRHSC) {
Value *Y;
// (X & C) or (X | C) or (X ^ C).
// (X << C) or (X >>_s C) or (X >>_u C).
Expand All @@ -9918,7 +9947,7 @@ void llvm::findValuesAffectedByCondition(
}
}
} else {
if (match(B, m_ConstantInt())) {
if (HasRHSC) {
// Handle (A + C1) u< C2, which is the canonical form of
// A > C3 && A < C4.
if (match(A, m_AddLike(m_Value(X), m_ConstantInt())))
Expand Down Expand Up @@ -9950,6 +9979,10 @@ void llvm::findValuesAffectedByCondition(
InsertAffected(X);
}
}

if (IsAssume && HasRHSC &&
match(A, m_Intrinsic<Intrinsic::ctpop>(m_Value(X))))
AddAffected(X);
} else if (match(Cond, m_FCmp(Pred, m_Value(A), m_Value(B)))) {
AddCmpOperands(A, B);

Expand Down
21 changes: 21 additions & 0 deletions llvm/test/Transforms/InstCombine/cttz.ll
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Expand Up @@ -276,3 +276,24 @@ define i32 @cttz_of_power_of_two_wrong_constant_2(i32 %x) {
%r = call i32 @llvm.cttz.i32(i32 %add, i1 false)
ret i32 %r
}

define i16 @cttz_assume(i16 %x) {
; CHECK-LABEL: @cttz_assume(
; CHECK-NEXT: [[ADD:%.*]] = add i16 [[X:%.*]], 1
; CHECK-NEXT: [[COND0:%.*]] = icmp ult i16 [[ADD]], 10
; CHECK-NEXT: call void @llvm.assume(i1 [[COND0]])
; CHECK-NEXT: [[COND1:%.*]] = icmp ne i16 [[X]], 0
; CHECK-NEXT: call void @llvm.assume(i1 [[COND1]])
; CHECK-NEXT: [[CTTZ:%.*]] = call range(i16 0, 17) i16 @llvm.cttz.i16(i16 [[X]], i1 true)
; CHECK-NEXT: ret i16 [[CTTZ]]
;
%add = add i16 %x, 1
%cond0 = icmp ult i16 %add, 10
call void @llvm.assume(i1 %cond0)

%cond1 = icmp ne i16 %x, 0
call void @llvm.assume(i1 %cond1)

%cttz = call i16 @llvm.cttz.i16(i16 %x, i1 false)
ret i16 %cttz
}
39 changes: 39 additions & 0 deletions llvm/test/Transforms/InstCombine/icmp.ll
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Expand Up @@ -5326,3 +5326,42 @@ define i1 @pr94897(i32 range(i32 -2147483648, 0) %x) {
%cmp = icmp ugt i32 %shl, -50331648
ret i1 %cmp
}

define i1 @icmp_and_inv_pow2_ne_0(i32 %A, i32 %B) {
; CHECK-LABEL: @icmp_and_inv_pow2_ne_0(
; CHECK-NEXT: [[POPCNT:%.*]] = tail call range(i32 0, 33) i32 @llvm.ctpop.i32(i32 [[A:%.*]])
; CHECK-NEXT: [[COND:%.*]] = icmp eq i32 [[POPCNT]], 1
; CHECK-NEXT: call void @llvm.assume(i1 [[COND]])
; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[A]], [[B:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[TMP1]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%popcnt = tail call i32 @llvm.ctpop.i32(i32 %A)
%cond = icmp eq i32 %popcnt, 1
call void @llvm.assume(i1 %cond)

%inv = xor i32 %B, -1
%and = and i32 %A, %inv
%cmp = icmp ne i32 %and, 0
ret i1 %cmp
}

define i1 @icmp_and_inv_pow2_or_zero_ne_0(i32 %A, i32 %B) {
; CHECK-LABEL: @icmp_and_inv_pow2_or_zero_ne_0(
; CHECK-NEXT: [[POPCNT:%.*]] = tail call range(i32 0, 33) i32 @llvm.ctpop.i32(i32 [[A:%.*]])
; CHECK-NEXT: [[COND:%.*]] = icmp ult i32 [[POPCNT]], 2
; CHECK-NEXT: call void @llvm.assume(i1 [[COND]])
; CHECK-NEXT: [[INV:%.*]] = xor i32 [[B:%.*]], -1
; CHECK-NEXT: [[AND:%.*]] = and i32 [[A]], [[INV]]
; CHECK-NEXT: [[CMP:%.*]] = icmp ne i32 [[AND]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%popcnt = tail call i32 @llvm.ctpop.i32(i32 %A)
%cond = icmp ult i32 %popcnt, 2
call void @llvm.assume(i1 %cond)

%inv = xor i32 %B, -1
%and = and i32 %A, %inv
%cmp = icmp ne i32 %and, 0
ret i1 %cmp
}
32 changes: 32 additions & 0 deletions llvm/test/Transforms/InstCombine/rem.ll
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Expand Up @@ -1041,3 +1041,35 @@ define <2 x i32> @PR62401(<2 x i1> %x, <2 x i32> %y) {
%r = urem <2 x i32> %y, %sext.i1
ret <2 x i32> %r
}

define i16 @rem_pow2_or_zero(i16 %x, i16 %y) {
; CHECK-LABEL: @rem_pow2_or_zero(
; CHECK-NEXT: [[POPCNT:%.*]] = call range(i16 1, 17) i16 @llvm.ctpop.i16(i16 [[Y:%.*]])
; CHECK-NEXT: [[COND:%.*]] = icmp ult i16 [[POPCNT]], 2
; CHECK-NEXT: tail call void @llvm.assume(i1 [[COND]])
; CHECK-NEXT: [[TMP1:%.*]] = add i16 [[Y]], -1
; CHECK-NEXT: [[REM:%.*]] = and i16 [[X:%.*]], [[TMP1]]
; CHECK-NEXT: ret i16 [[REM]]
;
%popcnt = call i16 @llvm.ctpop.i16(i16 %y)
%cond = icmp ult i16 %popcnt, 2
tail call void @llvm.assume(i1 %cond)
%rem = urem i16 %x, %y
ret i16 %rem
}

define i16 @rem_pow2(i16 %x, i16 %y) {
; CHECK-LABEL: @rem_pow2(
; CHECK-NEXT: [[POPCNT:%.*]] = call range(i16 1, 17) i16 @llvm.ctpop.i16(i16 [[Y:%.*]])
; CHECK-NEXT: [[COND:%.*]] = icmp eq i16 [[POPCNT]], 1
; CHECK-NEXT: tail call void @llvm.assume(i1 [[COND]])
; CHECK-NEXT: [[TMP1:%.*]] = add i16 [[Y]], -1
; CHECK-NEXT: [[REM:%.*]] = and i16 [[X:%.*]], [[TMP1]]
; CHECK-NEXT: ret i16 [[REM]]
;
%popcnt = call i16 @llvm.ctpop.i16(i16 %y)
%cond = icmp eq i16 %popcnt, 1
tail call void @llvm.assume(i1 %cond)
%rem = urem i16 %x, %y
ret i16 %rem
}
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