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Reland "[InstCombine] Fold (sub nuw X, (Y << nuw Z)) >>u exact Z --> (X >>u exact Z) sub nuw Y" #93571

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Merged
merged 2 commits into from
Jun 3, 2024
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Reland "[InstCombine] Fold (sub nuw X, (Y << nuw Z)) >>u exact Z --> (X >>u exact Z) sub nuw Y" #93571

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75dd3f0
[InstCombine] Pre-commit tests (NFC)
AZero13 May 7, 2024
23de287
[InstCombine] Fold (sub nuw X, (Y << nuw Z)) >>u exact Z --> (X >>u e…
AZero13 May 7, 2024
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11 changes: 11 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1275,6 +1275,17 @@ Instruction *InstCombinerImpl::visitLShr(BinaryOperator &I) {
return NewSub;
}

// (sub nuw X, (Y << nuw Z)) >>u exact Z --> (X >>u exact Z) sub nuw Y
if (I.isExact() &&
match(Op0, m_OneUse(m_NUWSub(m_Value(X),
m_NUWShl(m_Value(Y), m_Specific(Op1)))))) {
Value *NewLshr = Builder.CreateLShr(X, Op1, "", /*isExact=*/true);
auto *NewSub = BinaryOperator::CreateNUWSub(NewLshr, Y);
NewSub->setHasNoSignedWrap(
cast<OverflowingBinaryOperator>(Op0)->hasNoSignedWrap());
return NewSub;
}

auto isSuitableBinOpcode = [](Instruction::BinaryOps BinOpcode) {
switch (BinOpcode) {
default:
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113 changes: 113 additions & 0 deletions llvm/test/Transforms/InstCombine/lshr.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -464,6 +464,119 @@ define i32 @shl_sub_lshr(i32 %x, i32 %c, i32 %y) {
ret i32 %lshr
}

define i32 @shl_sub_lshr_reverse(i32 %x, i32 %c, i32 %y) {
; CHECK-LABEL: @shl_sub_lshr_reverse(
; CHECK-NEXT: [[TMP1:%.*]] = lshr exact i32 [[Y:%.*]], [[C:%.*]]
; CHECK-NEXT: [[LSHR:%.*]] = sub nuw nsw i32 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret i32 [[LSHR]]
;
%shl = shl nuw i32 %x, %c
%sub = sub nuw nsw i32 %y, %shl
%lshr = lshr exact i32 %sub, %c
ret i32 %lshr
}

define i32 @shl_sub_lshr_reverse_no_nsw(i32 %x, i32 %c, i32 %y) {
; CHECK-LABEL: @shl_sub_lshr_reverse_no_nsw(
; CHECK-NEXT: [[TMP1:%.*]] = lshr exact i32 [[Y:%.*]], [[C:%.*]]
; CHECK-NEXT: [[LSHR:%.*]] = sub nuw i32 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret i32 [[LSHR]]
;
%shl = shl nuw i32 %x, %c
%sub = sub nuw i32 %y, %shl
%lshr = lshr exact i32 %sub, %c
ret i32 %lshr
}

define i32 @shl_sub_lshr_reverse_nsw_on_op1(i32 %x, i32 %c, i32 %y) {
; CHECK-LABEL: @shl_sub_lshr_reverse_nsw_on_op1(
; CHECK-NEXT: [[TMP1:%.*]] = lshr exact i32 [[Y:%.*]], [[C:%.*]]
; CHECK-NEXT: [[LSHR:%.*]] = sub nuw i32 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret i32 [[LSHR]]
;
%shl = shl nuw nsw i32 %x, %c
%sub = sub nuw i32 %y, %shl
%lshr = lshr exact i32 %sub, %c
ret i32 %lshr
}

; Negative test

define i32 @shl_sub_lshr_reverse_no_exact(i32 %x, i32 %c, i32 %y) {
; CHECK-LABEL: @shl_sub_lshr_reverse_no_exact(
; CHECK-NEXT: [[SHL:%.*]] = shl nuw i32 [[X:%.*]], [[C:%.*]]
; CHECK-NEXT: [[SUB:%.*]] = sub nuw nsw i32 [[Y:%.*]], [[SHL]]
; CHECK-NEXT: [[LSHR:%.*]] = lshr i32 [[SUB]], [[C]]
; CHECK-NEXT: ret i32 [[LSHR]]
;
%shl = shl nuw i32 %x, %c
%sub = sub nuw nsw i32 %y, %shl
%lshr = lshr i32 %sub, %c
ret i32 %lshr
}

; Negative test

define i32 @shl_sub_lshr_reverse_multiuse(i32 %x, i32 %c, i32 %y) {
; CHECK-LABEL: @shl_sub_lshr_reverse_multiuse(
; CHECK-NEXT: [[SHL:%.*]] = shl nuw i32 [[X:%.*]], [[C:%.*]]
; CHECK-NEXT: [[SUB:%.*]] = sub nuw i32 [[Y:%.*]], [[SHL]]
; CHECK-NEXT: call void @use(i32 [[SUB]])
; CHECK-NEXT: [[LSHR:%.*]] = lshr exact i32 [[SUB]], [[C]]
; CHECK-NEXT: ret i32 [[LSHR]]
;
%shl = shl nuw i32 %x, %c
%sub = sub nuw i32 %y, %shl
call void @use(i32 %sub)
%lshr = lshr exact i32 %sub, %c
ret i32 %lshr
}

define i32 @shl_sub_lshr_reverse_multiuse2(i32 %x, i32 %c, i32 %y) {
; CHECK-LABEL: @shl_sub_lshr_reverse_multiuse2(
; CHECK-NEXT: [[SHL:%.*]] = shl nuw i32 [[X:%.*]], [[C:%.*]]
; CHECK-NEXT: call void @use(i32 [[SHL]])
; CHECK-NEXT: [[TMP1:%.*]] = lshr exact i32 [[Y:%.*]], [[C]]
; CHECK-NEXT: [[LSHR:%.*]] = sub nuw i32 [[TMP1]], [[X]]
; CHECK-NEXT: ret i32 [[LSHR]]
;
%shl = shl nuw i32 %x, %c
call void @use(i32 %shl)
%sub = sub nuw i32 %y, %shl
%lshr = lshr exact i32 %sub, %c
ret i32 %lshr
}

; Negative test

define i32 @shl_sub_lshr_reverse_no_nuw(i32 %x, i32 %c, i32 %y) {
; CHECK-LABEL: @shl_sub_lshr_reverse_no_nuw(
; CHECK-NEXT: [[SHL:%.*]] = shl i32 [[X:%.*]], [[C:%.*]]
; CHECK-NEXT: [[SUB:%.*]] = sub nuw i32 [[Y:%.*]], [[SHL]]
; CHECK-NEXT: [[LSHR:%.*]] = lshr exact i32 [[SUB]], [[C]]
; CHECK-NEXT: ret i32 [[LSHR]]
;
%shl = shl i32 %x, %c
%sub = sub nuw i32 %y, %shl
%lshr = lshr exact i32 %sub, %c
ret i32 %lshr
}

; Negative test

define i32 @shl_sub_lshr_reverse_no_nsw_2(i32 %x, i32 %c, i32 %y) {
; CHECK-LABEL: @shl_sub_lshr_reverse_no_nsw_2(
; CHECK-NEXT: [[SHL:%.*]] = shl nuw nsw i32 [[X:%.*]], [[C:%.*]]
; CHECK-NEXT: [[SUB:%.*]] = sub i32 [[Y:%.*]], [[SHL]]
; CHECK-NEXT: [[LSHR:%.*]] = lshr exact i32 [[SUB]], [[C]]
; CHECK-NEXT: ret i32 [[LSHR]]
;
%shl = shl nuw nsw i32 %x, %c
%sub = sub i32 %y, %shl
%lshr = lshr exact i32 %sub, %c
ret i32 %lshr
}

define i32 @shl_or_lshr(i32 %x, i32 %c, i32 %y) {
; CHECK-LABEL: @shl_or_lshr(
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[Y:%.*]], [[C:%.*]]
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