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[InstCombine] Detect different vscales in div by shift combine. #126411

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[InstCombine] Detect different vscales in div by shift combine. #126411

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4b0a7e6
[InstCombine] Add an extra test for udiv_shl_pair_const with vscale
davemgreen Feb 8, 2025
0e8caf4
[InstCombine] Detect different vscales in div by shift combine.
davemgreen Feb 9, 2025
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8 changes: 5 additions & 3 deletions llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1205,14 +1205,16 @@ static Value *foldIDivShl(BinaryOperator &I, InstCombiner::BuilderTy &Builder) {

// 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)))) {
if ((match(Op0, m_Shl(m_Value(X), m_Value(Y))) &&
match(Op1, m_Shl(m_Specific(X), m_Value(Z)))) ||
(match(Op0, m_Shl(m_VScale(), m_Value(Y))) &&
match(Op1, m_Shl(m_VScale(), 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);
Constant *One = ConstantInt::get(Op0->getType(), 1);
// Only preserve the nsw flag if dividend has nsw
// or divisor has nsw and operator is sdiv.
Value *Dividend = Builder.CreateShl(
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11 changes: 11 additions & 0 deletions llvm/test/Transforms/InstCombine/AArch64/sve-intrinsic-opts-counting-elems.ll
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Expand Up @@ -240,6 +240,17 @@ define i64 @cntd_all() {
}


define i64 @udiv() vscale_range(1, 16) {
; CHECK-LABEL: @udiv(
; CHECK-NEXT: ret i64 4
;
%a = call i64 @llvm.aarch64.sve.cntb(i32 31)
%b = call i64 @llvm.aarch64.sve.cntw(i32 31)
%c = udiv i64 %a, %b
ret i64 %c
}


declare i64 @llvm.aarch64.sve.cntb(i32 %pattern)
declare i64 @llvm.aarch64.sve.cnth(i32 %pattern)
declare i64 @llvm.aarch64.sve.cntw(i32 %pattern)
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14 changes: 14 additions & 0 deletions llvm/test/Transforms/InstCombine/div-shift.ll
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Expand Up @@ -1399,3 +1399,17 @@ start:
%div = udiv i8 %x, %y
ret i8 %div
}

define i32 @udiv_shl_pair_const_vscale() vscale_range(1, 16) {
; CHECK-LABEL: @udiv_shl_pair_const_vscale(
; CHECK-NEXT: entry:
; CHECK-NEXT: ret i32 2
;
entry:
%a = call i32 @llvm.vscale()
%b = call i32 @llvm.vscale()
%lhs = shl nuw i32 %a, 2
%rhs = shl nuw i32 %b, 1
%div = udiv i32 %lhs, %rhs
ret i32 %div
}