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[InstCombine] Fold (X << Y) / (X << Z) -> 1 << Y >> Z #68863

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Merged
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Oct 15, 2023
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[InstCombine] Fold (X << Y) / (X << Z) -> 1 << Y >> Z #68863

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ec0fe25
[InstCombine][NFC] Precommit tests for PR68857
XChy Oct 12, 2023
3ab9161
[InstCombine] Fold (A<<X)/(A<<Y) -> 1<<X>>Y
XChy Oct 12, 2023
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22 changes: 22 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -980,6 +980,28 @@ static Instruction *foldIDivShl(BinaryOperator &I,
Ret = BinaryOperator::CreateSDiv(X, Y);
}

// If X << Y and X << Z does not overflow, then:
// (X << Y) / (X << Z) -> (1 << Y) / (1 << Z) -> 1 << Y >> Z
if (match(Op0, m_Shl(m_Value(X), m_Value(Y))) &&
match(Op1, m_Shl(m_Specific(X), m_Value(Z)))) {
auto *Shl0 = cast<OverflowingBinaryOperator>(Op0);
auto *Shl1 = cast<OverflowingBinaryOperator>(Op1);

if (IsSigned ? (Shl0->hasNoSignedWrap() && Shl1->hasNoSignedWrap())
: (Shl0->hasNoUnsignedWrap() && Shl1->hasNoUnsignedWrap())) {
Constant *One = ConstantInt::get(X->getType(), 1);
// Only preserve the nsw flag if dividend has nsw
// or divisor has nsw and operator is sdiv.
Value *Dividend = Builder.CreateShl(
One, Y, "shl.dividend",
/*HasNUW*/ true,
/*HasNSW*/
IsSigned ? (Shl0->hasNoUnsignedWrap() || Shl1->hasNoUnsignedWrap())
: Shl0->hasNoSignedWrap());
Ret = BinaryOperator::CreateLShr(Dividend, Z);
}
}

if (!Ret)
return nullptr;

Expand Down
255 changes: 255 additions & 0 deletions llvm/test/Transforms/InstCombine/div-shift.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
; RUN: opt < %s -passes=instcombine -S | FileCheck %s

declare void @use(i8)
declare void @use32(i32)

declare i8 @llvm.umin.i8(i8, i8)
declare i8 @llvm.umax.i8(i8, i8)
Expand Down Expand Up @@ -1025,3 +1026,257 @@ define i8 @udiv_shl_no_overflow(i8 %x, i8 %y) {
%mul = udiv i8 %x, %min
ret i8 %mul
}

; (X<<Y) / (X<<Z) -> 1 << Y >> Z

define i32 @sdiv_shl_pair_const(i32 %a) {
; CHECK-LABEL: @sdiv_shl_pair_const(
; CHECK-NEXT: entry:
; CHECK-NEXT: ret i32 2
;
entry:
%lhs = shl nsw i32 %a, 2
%rhs = shl nsw i32 %a, 1
%div = sdiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @udiv_shl_pair_const(i32 %a) {
; CHECK-LABEL: @udiv_shl_pair_const(
; CHECK-NEXT: entry:
; CHECK-NEXT: ret i32 2
;
entry:
%lhs = shl nuw i32 %a, 2
%rhs = shl nuw i32 %a, 1
%div = udiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @sdiv_shl_pair1(i32 %a, i32 %x, i32 %y) {
; CHECK-LABEL: @sdiv_shl_pair1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SHL_DIVIDEND:%.*]] = shl nuw nsw i32 1, [[X:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = lshr i32 [[SHL_DIVIDEND]], [[Y:%.*]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl nsw i32 %a, %x
%rhs = shl nuw nsw i32 %a, %y
%div = sdiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @sdiv_shl_pair2(i32 %a, i32 %x, i32 %y) {
; CHECK-LABEL: @sdiv_shl_pair2(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SHL_DIVIDEND:%.*]] = shl nuw nsw i32 1, [[X:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = lshr i32 [[SHL_DIVIDEND]], [[Y:%.*]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl nuw nsw i32 %a, %x
%rhs = shl nsw i32 %a, %y
%div = sdiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @sdiv_shl_pair3(i32 %a, i32 %x, i32 %y) {
; CHECK-LABEL: @sdiv_shl_pair3(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SHL_DIVIDEND:%.*]] = shl nuw i32 1, [[X:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = lshr i32 [[SHL_DIVIDEND]], [[Y:%.*]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl nsw i32 %a, %x
%rhs = shl nsw i32 %a, %y
%div = sdiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @sdiv_shl_no_pair_fail(i32 %a, i32 %b, i32 %x, i32 %y) {
; CHECK-LABEL: @sdiv_shl_no_pair_fail(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[LHS:%.*]] = shl nuw nsw i32 [[A:%.*]], [[X:%.*]]
; CHECK-NEXT: [[RHS:%.*]] = shl nuw i32 [[B:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = sdiv i32 [[LHS]], [[RHS]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl nuw nsw i32 %a, %x
%rhs = shl nuw i32 %b, %y
%div = sdiv i32 %lhs, %rhs
ret i32 %div
}
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@XChy XChy Oct 13, 2023

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Different LHS test here.


define i32 @udiv_shl_pair1(i32 %a, i32 %x, i32 %y) {
; CHECK-LABEL: @udiv_shl_pair1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SHL_DIVIDEND:%.*]] = shl nuw i32 1, [[X:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = lshr i32 [[SHL_DIVIDEND]], [[Y:%.*]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl nuw i32 %a, %x
%rhs = shl nuw i32 %a, %y
%div = udiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @udiv_shl_pair2(i32 %a, i32 %x, i32 %y) {
; CHECK-LABEL: @udiv_shl_pair2(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SHL_DIVIDEND:%.*]] = shl nuw nsw i32 1, [[X:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = lshr i32 [[SHL_DIVIDEND]], [[Y:%.*]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl nuw nsw i32 %a, %x
%rhs = shl nuw i32 %a, %y
%div = udiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @udiv_shl_pair3(i32 %a, i32 %x, i32 %y) {
; CHECK-LABEL: @udiv_shl_pair3(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SHL_DIVIDEND:%.*]] = shl nuw i32 1, [[X:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = lshr i32 [[SHL_DIVIDEND]], [[Y:%.*]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl nuw i32 %a, %x
%rhs = shl nuw nsw i32 %a, %y
%div = udiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @sdiv_shl_pair_overflow_fail1(i32 %a, i32 %x, i32 %y) {
; CHECK-LABEL: @sdiv_shl_pair_overflow_fail1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[LHS:%.*]] = shl i32 [[A:%.*]], [[X:%.*]]
; CHECK-NEXT: [[RHS:%.*]] = shl nsw i32 [[A]], [[Y:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = sdiv i32 [[LHS]], [[RHS]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl i32 %a, %x
%rhs = shl nsw i32 %a, %y
%div = sdiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @sdiv_shl_pair_overflow_fail2(i32 %a, i32 %x, i32 %y) {
; CHECK-LABEL: @sdiv_shl_pair_overflow_fail2(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[LHS:%.*]] = shl nsw i32 [[A:%.*]], [[X:%.*]]
; CHECK-NEXT: [[RHS:%.*]] = shl nuw i32 [[A]], [[Y:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = sdiv i32 [[LHS]], [[RHS]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl nsw i32 %a, %x
%rhs = shl nuw i32 %a, %y
%div = sdiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @udiv_shl_pair_overflow_fail1(i32 %a, i32 %x, i32 %y) {
; CHECK-LABEL: @udiv_shl_pair_overflow_fail1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[LHS:%.*]] = shl nsw i32 [[A:%.*]], [[X:%.*]]
; CHECK-NEXT: [[RHS:%.*]] = shl nuw i32 [[A]], [[Y:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = udiv i32 [[LHS]], [[RHS]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl nsw i32 %a, %x
%rhs = shl nuw i32 %a, %y
%div = udiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @udiv_shl_pair_overflow_fail2(i32 %a, i32 %x, i32 %y) {
; CHECK-LABEL: @udiv_shl_pair_overflow_fail2(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[LHS:%.*]] = shl nsw i32 [[A:%.*]], [[X:%.*]]
; CHECK-NEXT: [[RHS:%.*]] = shl i32 [[A]], [[Y:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = udiv i32 [[LHS]], [[RHS]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl nsw i32 %a, %x
%rhs = shl i32 %a, %y
%div = udiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @udiv_shl_pair_overflow_fail3(i32 %a, i32 %x, i32 %y) {
; CHECK-LABEL: @udiv_shl_pair_overflow_fail3(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[LHS:%.*]] = shl nuw nsw i32 [[A:%.*]], [[X:%.*]]
; CHECK-NEXT: [[RHS:%.*]] = shl i32 [[A]], [[Y:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = udiv i32 [[LHS]], [[RHS]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl nuw nsw i32 %a, %x
%rhs = shl i32 %a, %y
%div = udiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @sdiv_shl_pair_multiuse1(i32 %a, i32 %x, i32 %y) {
; CHECK-LABEL: @sdiv_shl_pair_multiuse1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[LHS:%.*]] = shl nuw nsw i32 [[A:%.*]], [[X:%.*]]
; CHECK-NEXT: call void @use32(i32 [[LHS]])
; CHECK-NEXT: [[SHL_DIVIDEND:%.*]] = shl nuw nsw i32 1, [[X]]
; CHECK-NEXT: [[DIV:%.*]] = lshr i32 [[SHL_DIVIDEND]], [[Y:%.*]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl nuw nsw i32 %a, %x
call void @use32(i32 %lhs)
%rhs = shl nsw i32 %a, %y
%div = sdiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @sdiv_shl_pair_multiuse2(i32 %a, i32 %x, i32 %y) {
; CHECK-LABEL: @sdiv_shl_pair_multiuse2(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[RHS:%.*]] = shl nsw i32 [[A:%.*]], [[Y:%.*]]
; CHECK-NEXT: call void @use32(i32 [[RHS]])
; CHECK-NEXT: [[SHL_DIVIDEND:%.*]] = shl nuw nsw i32 1, [[X:%.*]]
; CHECK-NEXT: [[DIV:%.*]] = lshr i32 [[SHL_DIVIDEND]], [[Y]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl nuw nsw i32 %a, %x
%rhs = shl nsw i32 %a, %y
call void @use32(i32 %rhs)
%div = sdiv i32 %lhs, %rhs
ret i32 %div
}

define i32 @sdiv_shl_pair_multiuse3(i32 %a, i32 %x, i32 %y) {
; CHECK-LABEL: @sdiv_shl_pair_multiuse3(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[LHS:%.*]] = shl nuw nsw i32 [[A:%.*]], [[X:%.*]]
; CHECK-NEXT: [[RHS:%.*]] = shl nsw i32 [[A]], [[Y:%.*]]
; CHECK-NEXT: call void @use32(i32 [[LHS]])
; CHECK-NEXT: call void @use32(i32 [[RHS]])
; CHECK-NEXT: [[SHL_DIVIDEND:%.*]] = shl nuw nsw i32 1, [[X]]
; CHECK-NEXT: [[DIV:%.*]] = lshr i32 [[SHL_DIVIDEND]], [[Y]]
; CHECK-NEXT: ret i32 [[DIV]]
;
entry:
%lhs = shl nuw nsw i32 %a, %x
%rhs = shl nsw i32 %a, %y
call void @use32(i32 %lhs)
call void @use32(i32 %rhs)
%div = sdiv i32 %lhs, %rhs
ret i32 %div
}