Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

[InstCombine] Handle ceil division idiom #100977

Open
wants to merge 7 commits into
base: main
Choose a base branch
from
Open

[InstCombine] Handle ceil division idiom #100977

Show file tree
Hide file tree
Changes from 5 commits
Commits
Show all changes
7 commits
Select commit Hold shift + click to select a range
91d8aea
[InstCombine] Introduce test for PR100977 (NFC)
antoniofrighetto Jul 29, 2024
af0d68c
[InstCombine] Handle ceil division idiom
antoniofrighetto Jul 29, 2024
b9593d2
!fixup change to m_value
antoniofrighetto Jul 29, 2024
cdf886f
!fixup pow2 no zero
antoniofrighetto Jul 29, 2024
8552378
!fixup drop oneuse in shift amount
antoniofrighetto Jul 30, 2024
4e5cd1a
!fixup style
antoniofrighetto Jul 30, 2024
cca259c
!fixup style
antoniofrighetto Jul 30, 2024
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
94 changes: 70 additions & 24 deletions llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1250,6 +1250,74 @@ static Instruction *foldToUnsignedSaturatedAdd(BinaryOperator &I) {
return nullptr;
}

static Value *foldCeilIdioms(BinaryOperator &I, InstCombinerImpl &IC) {
assert(I.getOpcode() == Instruction::Add && "Expecting add instruction.");
Value *A, *B;
ICmpInst::Predicate Pred;
auto &ICB = IC.Builder;

// Fold the log2 ceil idiom:
// zext (ctpop(A) >u/!= 1) + (ctlz (A, true) ^ (BW - 1))
// -> BW - ctlz (A - 1, false)
const APInt *XorC;
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Why did you merge the log2 ceil part into this function? I don't think they share common code.

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

They do not, but they do both involve the ceil part, thus I thought it was nice to batch them together under a single foldCeilIdioms.

if (match(&I,
m_c_Add(
m_ZExt(m_ICmp(Pred, m_Intrinsic<Intrinsic::ctpop>(m_Value(A)),
m_One())),
m_OneUse(m_ZExtOrSelf(m_OneUse(m_Xor(
m_OneUse(m_TruncOrSelf(m_OneUse(
m_Intrinsic<Intrinsic::ctlz>(m_Deferred(A), m_One())))),
m_APInt(XorC))))))) &&
(Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_NE) &&
*XorC == A->getType()->getScalarSizeInBits() - 1) {
Value *Sub = ICB.CreateAdd(A, Constant::getAllOnesValue(A->getType()));
Value *Ctlz = ICB.CreateIntrinsic(Intrinsic::ctlz, {A->getType()},
{Sub, ICB.getFalse()});
Value *Ret = ICB.CreateSub(
ConstantInt::get(A->getType(), A->getType()->getScalarSizeInBits()),
Ctlz, "", /*HasNUW*/ true, /*HasNSW*/ true);
return ICB.CreateZExtOrTrunc(Ret, I.getType());
}

// Fold the ceil division idiom:
// add (udiv (sub A, Bias), B), Bias
// -> udiv (add A, B - 1), B)
// with Bias = A != 0; A + B not to overflow
auto MatchDivision = [&IC](Instruction *Div, Value *&DivOp0, Value *&DivOp1) {
if (match(Div, m_UDiv(m_Value(DivOp0), m_Value(DivOp1))))
return true;

Value *N;
const APInt *C;
if (match(Div, m_LShr(m_Value(DivOp0), m_Value(N))) &&
match(N, m_Sub(m_APInt(C), m_Intrinsic<Intrinsic::ctlz>(m_Value(DivOp1),
antoniofrighetto marked this conversation as resolved.
Show resolved Hide resolved
m_Zero()))) &&
(*C == Div->getType()->getScalarSizeInBits() - 1) &&
IC.isKnownToBeAPowerOfTwo(DivOp1, /*OrZero*/ false, 0, Div))
return true;

return false;
};

Instruction *Div;
Value *Bias, *Sub;
if (match(&I, m_c_Add(m_Instruction(Div), m_Value(Bias))) &&
MatchDivision(Div, Sub, B) &&
match(Sub, m_Sub(m_Value(A), m_Value(Bias))) &&
match(Bias, m_ZExt(m_ICmp(Pred, m_Specific(A), m_ZeroInt()))) &&
antoniofrighetto marked this conversation as resolved.
Show resolved Hide resolved
Pred == ICmpInst::ICMP_NE && Bias->hasNUses(2)) {
WithCache<const Value *> LHSCache(A), RHSCache(B);
auto OR = IC.computeOverflowForUnsignedAdd(LHSCache, RHSCache, &I);
if (OR == OverflowResult::NeverOverflows) {
auto *BMinusOne =
ICB.CreateAdd(B, Constant::getAllOnesValue(I.getType()));
return ICB.CreateUDiv(ICB.CreateAdd(A, BMinusOne), B);
}
}

return nullptr;
}

// Transform:
// (add A, (shl (neg B), Y))
// -> (sub A, (shl B, Y))
Expand Down Expand Up @@ -1785,30 +1853,8 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
I, Builder.CreateIntrinsic(Intrinsic::ctpop, {I.getType()},
{Builder.CreateOr(A, B)}));

// Fold the log2_ceil idiom:
// zext(ctpop(A) >u/!= 1) + (ctlz(A, true) ^ (BW - 1))
// -->
// BW - ctlz(A - 1, false)
const APInt *XorC;
ICmpInst::Predicate Pred;
if (match(&I,
m_c_Add(
m_ZExt(m_ICmp(Pred, m_Intrinsic<Intrinsic::ctpop>(m_Value(A)),
m_One())),
m_OneUse(m_ZExtOrSelf(m_OneUse(m_Xor(
m_OneUse(m_TruncOrSelf(m_OneUse(
m_Intrinsic<Intrinsic::ctlz>(m_Deferred(A), m_One())))),
m_APInt(XorC))))))) &&
(Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_NE) &&
*XorC == A->getType()->getScalarSizeInBits() - 1) {
Value *Sub = Builder.CreateAdd(A, Constant::getAllOnesValue(A->getType()));
Value *Ctlz = Builder.CreateIntrinsic(Intrinsic::ctlz, {A->getType()},
{Sub, Builder.getFalse()});
Value *Ret = Builder.CreateSub(
ConstantInt::get(A->getType(), A->getType()->getScalarSizeInBits()),
Ctlz, "", /*HasNUW*/ true, /*HasNSW*/ true);
return replaceInstUsesWith(I, Builder.CreateZExtOrTrunc(Ret, I.getType()));
}
if (Value *V = foldCeilIdioms(I, *this))
return replaceInstUsesWith(I, V);

if (Instruction *Res = foldSquareSumInt(I))
return Res;
Expand Down
213 changes: 213 additions & 0 deletions llvm/test/Transforms/InstCombine/fold-ceil-div-idiom.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,213 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
; RUN: opt < %s -passes=instcombine -S | FileCheck %s

define i8 @ceil_div_idiom(i8 %x, i8 %y) {
; CHECK-LABEL: define i8 @ceil_div_idiom(
; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
; CHECK-NEXT: [[WO:%.*]] = call { i8, i1 } @llvm.uadd.with.overflow.i8(i8 [[X]], i8 [[Y]])
; CHECK-NEXT: [[OV:%.*]] = extractvalue { i8, i1 } [[WO]], 1
; CHECK-NEXT: [[OV_NOT:%.*]] = xor i1 [[OV]], true
; CHECK-NEXT: call void @llvm.assume(i1 [[OV_NOT]])
; CHECK-NEXT: [[NONZERO:%.*]] = icmp ne i8 [[X]], 0
; CHECK-NEXT: [[BIAS:%.*]] = zext i1 [[NONZERO]] to i8
; CHECK-NEXT: [[SUB:%.*]] = sub i8 [[X]], [[BIAS]]
; CHECK-NEXT: [[DIV:%.*]] = udiv i8 [[SUB]], [[Y]]
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[DIV]], [[BIAS]]
; CHECK-NEXT: ret i8 [[ADD]]
;
%wo = call {i8, i1} @llvm.uadd.with.overflow(i8 %x, i8 %y)
%ov = extractvalue {i8, i1} %wo, 1
%ov.not = xor i1 %ov, true
call void @llvm.assume(i1 %ov.not)

%nonzero = icmp ne i8 %x, 0
%bias = zext i1 %nonzero to i8
%sub = sub i8 %x, %bias
%div = udiv i8 %sub, %y
%add = add i8 %div, %bias
ret i8 %add
}

define i8 @ceil_div_idiom_2(i8 %x, i8 %y) {
; CHECK-LABEL: define i8 @ceil_div_idiom_2(
; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
; CHECK-NEXT: [[OV_NOT:%.*]] = add nuw i8 [[X]], [[Y]]
; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[OV_NOT]] to i1
; CHECK-NEXT: call void @llvm.assume(i1 [[TRUNC]])
; CHECK-NEXT: [[NONZERO:%.*]] = icmp ne i8 [[X]], 0
; CHECK-NEXT: [[BIAS:%.*]] = zext i1 [[NONZERO]] to i8
; CHECK-NEXT: [[SUB:%.*]] = sub i8 [[X]], [[BIAS]]
; CHECK-NEXT: [[DIV:%.*]] = udiv i8 [[SUB]], [[Y]]
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[DIV]], [[BIAS]]
; CHECK-NEXT: ret i8 [[ADD]]
;
%ov.not = add nuw i8 %x, %y
%trunc = trunc i8 %ov.not to i1
call void @llvm.assume(i1 %trunc)

%nonzero = icmp ne i8 %x, 0
%bias = zext i1 %nonzero to i8
%sub = sub i8 %x, %bias
%div = udiv i8 %sub, %y
%add = add i8 %div, %bias
ret i8 %add
}

define i8 @ceil_div_idiom_with_lshr(i8 %x, i8 %y) {
; CHECK-LABEL: define i8 @ceil_div_idiom_with_lshr(
; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
; CHECK-NEXT: [[WO:%.*]] = call { i8, i1 } @llvm.uadd.with.overflow.i8(i8 [[X]], i8 [[Y]])
; CHECK-NEXT: [[OV:%.*]] = extractvalue { i8, i1 } [[WO]], 1
; CHECK-NEXT: [[OV_NOT:%.*]] = xor i1 [[OV]], true
; CHECK-NEXT: call void @llvm.assume(i1 [[OV_NOT]])
; CHECK-NEXT: [[CTPOPULATION:%.*]] = call range(i8 0, 9) i8 @llvm.ctpop.i8(i8 [[Y]])
; CHECK-NEXT: [[IS_POW_2:%.*]] = icmp eq i8 [[CTPOPULATION]], 1
; CHECK-NEXT: call void @llvm.assume(i1 [[IS_POW_2]])
; CHECK-NEXT: [[NONZERO:%.*]] = icmp ne i8 [[X]], 0
; CHECK-NEXT: [[BIAS:%.*]] = zext i1 [[NONZERO]] to i8
; CHECK-NEXT: [[SUB:%.*]] = sub i8 [[X]], [[BIAS]]
; CHECK-NEXT: [[CTLZ:%.*]] = tail call range(i8 0, 9) i8 @llvm.ctlz.i8(i8 [[Y]], i1 true)
; CHECK-NEXT: [[N:%.*]] = xor i8 [[CTLZ]], 7
; CHECK-NEXT: [[DIV:%.*]] = lshr i8 [[SUB]], [[N]]
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[DIV]], [[BIAS]]
; CHECK-NEXT: ret i8 [[ADD]]
;
%wo = call {i8, i1} @llvm.uadd.with.overflow(i8 %x, i8 %y)
%ov = extractvalue {i8, i1} %wo, 1
%ov.not = xor i1 %ov, true
call void @llvm.assume(i1 %ov.not)

%ctpopulation = call i8 @llvm.ctpop.i8(i8 %y)
%is_pow_2 = icmp eq i8 %ctpopulation, 1
call void @llvm.assume(i1 %is_pow_2)

%nonzero = icmp ne i8 %x, 0
%bias = zext i1 %nonzero to i8
%sub = sub i8 %x, %bias
%ctlz = tail call i8 @llvm.ctlz.i8(i8 %y, i1 true)
%n = sub i8 7, %ctlz
%div = lshr i8 %sub, %n
%add = add i8 %div, %bias
ret i8 %add
}

define i8 @ceil_div_idiom_add_may_overflow(i8 %x, i8 %y) {
; CHECK-LABEL: define i8 @ceil_div_idiom_add_may_overflow(
; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
; CHECK-NEXT: [[NONZERO:%.*]] = icmp ne i8 [[X]], 0
; CHECK-NEXT: [[BIAS:%.*]] = zext i1 [[NONZERO]] to i8
; CHECK-NEXT: [[SUB:%.*]] = sub i8 [[X]], [[BIAS]]
; CHECK-NEXT: [[DIV:%.*]] = udiv i8 [[SUB]], [[Y]]
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[DIV]], [[BIAS]]
; CHECK-NEXT: ret i8 [[ADD]]
;
%nonzero = icmp ne i8 %x, 0
%bias = zext i1 %nonzero to i8
%sub = sub i8 %x, %bias
%div = udiv i8 %sub, %y
%add = add i8 %div, %bias
ret i8 %add
}

define i8 @ceil_div_idiom_multiuse_bias(i8 %x, i8 %y) {
; CHECK-LABEL: define i8 @ceil_div_idiom_multiuse_bias(
; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
; CHECK-NEXT: [[WO:%.*]] = call { i8, i1 } @llvm.uadd.with.overflow.i8(i8 [[X]], i8 [[Y]])
; CHECK-NEXT: [[OV:%.*]] = extractvalue { i8, i1 } [[WO]], 1
; CHECK-NEXT: [[OV_NOT:%.*]] = xor i1 [[OV]], true
; CHECK-NEXT: call void @llvm.assume(i1 [[OV_NOT]])
; CHECK-NEXT: [[NONZERO:%.*]] = icmp ne i8 [[X]], 0
; CHECK-NEXT: [[BIAS:%.*]] = zext i1 [[NONZERO]] to i8
; CHECK-NEXT: [[SUB:%.*]] = sub i8 [[X]], [[BIAS]]
; CHECK-NEXT: [[DIV:%.*]] = udiv i8 [[SUB]], [[Y]]
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[DIV]], [[BIAS]]
; CHECK-NEXT: call void @use(i8 [[BIAS]])
; CHECK-NEXT: ret i8 [[ADD]]
;
%wo = call {i8, i1} @llvm.uadd.with.overflow(i8 %x, i8 %y)
%ov = extractvalue {i8, i1} %wo, 1
%ov.not = xor i1 %ov, true
call void @llvm.assume(i1 %ov.not)

%nonzero = icmp ne i8 %x, 0
%bias = zext i1 %nonzero to i8
%sub = sub i8 %x, %bias
%div = udiv i8 %sub, %y
%add = add i8 %div, %bias
call void @use(i8 %bias)
ret i8 %add
}

define i8 @ceil_div_idiom_with_lshr_not_power_2(i8 %x, i8 %y) {
; CHECK-LABEL: define i8 @ceil_div_idiom_with_lshr_not_power_2(
; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
; CHECK-NEXT: [[WO:%.*]] = call { i8, i1 } @llvm.uadd.with.overflow.i8(i8 [[X]], i8 [[Y]])
; CHECK-NEXT: [[OV:%.*]] = extractvalue { i8, i1 } [[WO]], 1
; CHECK-NEXT: [[OV_NOT:%.*]] = xor i1 [[OV]], true
; CHECK-NEXT: call void @llvm.assume(i1 [[OV_NOT]])
; CHECK-NEXT: [[NONZERO:%.*]] = icmp ne i8 [[X]], 0
; CHECK-NEXT: [[BIAS:%.*]] = zext i1 [[NONZERO]] to i8
; CHECK-NEXT: [[SUB:%.*]] = sub i8 [[X]], [[BIAS]]
; CHECK-NEXT: [[CTLZ:%.*]] = tail call range(i8 0, 9) i8 @llvm.ctlz.i8(i8 [[Y]], i1 true)
; CHECK-NEXT: [[N:%.*]] = xor i8 [[CTLZ]], 7
; CHECK-NEXT: [[DIV:%.*]] = lshr i8 [[SUB]], [[N]]
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[DIV]], [[BIAS]]
; CHECK-NEXT: ret i8 [[ADD]]
;
%wo = call {i8, i1} @llvm.uadd.with.overflow(i8 %x, i8 %y)
%ov = extractvalue {i8, i1} %wo, 1
%ov.not = xor i1 %ov, true
call void @llvm.assume(i1 %ov.not)

%nonzero = icmp ne i8 %x, 0
%bias = zext i1 %nonzero to i8
%sub = sub i8 %x, %bias
%ctlz = tail call i8 @llvm.ctlz.i8(i8 %y, i1 true)
%n = sub i8 7, %ctlz
%div = lshr i8 %sub, %n
%add = add i8 %div, %bias
ret i8 %add
}

define i8 @ceil_div_idiom_with_lshr_wrong_bw(i8 %x, i8 %y) {
; CHECK-LABEL: define i8 @ceil_div_idiom_with_lshr_wrong_bw(
; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
; CHECK-NEXT: [[WO:%.*]] = call { i8, i1 } @llvm.uadd.with.overflow.i8(i8 [[X]], i8 [[Y]])
; CHECK-NEXT: [[OV:%.*]] = extractvalue { i8, i1 } [[WO]], 1
; CHECK-NEXT: [[OV_NOT:%.*]] = xor i1 [[OV]], true
; CHECK-NEXT: call void @llvm.assume(i1 [[OV_NOT]])
; CHECK-NEXT: [[CTPOPULATION:%.*]] = call range(i8 0, 9) i8 @llvm.ctpop.i8(i8 [[Y]])
; CHECK-NEXT: [[IS_POW_2:%.*]] = icmp eq i8 [[CTPOPULATION]], 1
; CHECK-NEXT: call void @llvm.assume(i1 [[IS_POW_2]])
; CHECK-NEXT: [[NONZERO:%.*]] = icmp ne i8 [[X]], 0
; CHECK-NEXT: [[BIAS:%.*]] = zext i1 [[NONZERO]] to i8
; CHECK-NEXT: [[SUB:%.*]] = sub i8 [[X]], [[BIAS]]
; CHECK-NEXT: [[CTLZ:%.*]] = tail call range(i8 0, 9) i8 @llvm.ctlz.i8(i8 [[Y]], i1 true)
; CHECK-NEXT: [[N:%.*]] = sub nuw nsw i8 8, [[CTLZ]]
; CHECK-NEXT: [[DIV:%.*]] = lshr i8 [[SUB]], [[N]]
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[DIV]], [[BIAS]]
; CHECK-NEXT: ret i8 [[ADD]]
;
%wo = call {i8, i1} @llvm.uadd.with.overflow(i8 %x, i8 %y)
%ov = extractvalue {i8, i1} %wo, 1
%ov.not = xor i1 %ov, true
call void @llvm.assume(i1 %ov.not)

%ctpopulation = call i8 @llvm.ctpop.i8(i8 %y)
%is_pow_2 = icmp eq i8 %ctpopulation, 1
call void @llvm.assume(i1 %is_pow_2)

%nonzero = icmp ne i8 %x, 0
%bias = zext i1 %nonzero to i8
%sub = sub i8 %x, %bias
%ctlz = tail call i8 @llvm.ctlz.i8(i8 %y, i1 true)
%n = sub i8 8, %ctlz
%div = lshr i8 %sub, %n
%add = add i8 %div, %bias
ret i8 %add
}

declare { i8, i1 } @llvm.uadd.with.overflow.i8(i8, i8)
declare i8 @llvm.ctpop.i8(i8)
declare void @llvm.assume(i1)
declare void @use(i8)
Loading