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[InstCombine] Detect (x ^ -x) as a ~Mask #84868

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[InstCombine] Detect (x ^ -x) as a ~Mask #84868

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854777d
[InstCombine] Add test for detecting `(x ^ -x)` as a ~Mask; NFC
goldsteinn Mar 12, 2024
5237dda
[InstCombine] Detect `(x ^ -x)` as a ~Mask
goldsteinn Mar 12, 2024
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7 changes: 5 additions & 2 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4113,9 +4113,12 @@ static bool isMaskOrZero(const Value *V, bool Not, const SimplifyQuery &Q,
if (match(V, m_Not(m_Value(X))))
return isMaskOrZero(X, !Not, Q, Depth);

// (X ^ -X) is a ~Mask
if (Not)
return match(V, m_c_Xor(m_Value(X), m_Neg(m_Deferred(X))));
// (X ^ (X - 1)) is a Mask
return !Not &&
match(V, m_c_Xor(m_Value(X), m_Add(m_Deferred(X), m_AllOnes())));
else
return match(V, m_c_Xor(m_Value(X), m_Add(m_Deferred(X), m_AllOnes())));
case Instruction::Select:
// c ? Mask0 : Mask1 is a Mask.
return isMaskOrZero(I->getOperand(1), Not, Q, Depth) &&
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18 changes: 18 additions & 0 deletions llvm/test/Transforms/InstCombine/icmp-and-lowbit-mask.ll
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Expand Up @@ -453,6 +453,24 @@ define i1 @src_is_notmask_shl(i8 %x_in, i8 %y, i1 %cond) {
ret i1 %r
}

define i1 @src_is_notmask_x_xor_neg_x(i8 %x_in, i8 %y, i1 %cond) {
; CHECK-LABEL: @src_is_notmask_x_xor_neg_x(
; CHECK-NEXT: [[X:%.*]] = xor i8 [[X_IN:%.*]], 123
; CHECK-NEXT: [[NEG_Y:%.*]] = add i8 [[Y:%.*]], -1
; CHECK-NEXT: [[NOTMASK0:%.*]] = xor i8 [[NEG_Y]], [[Y]]
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i8 [[NOTMASK0]], i8 7
; CHECK-NEXT: [[R:%.*]] = icmp ule i8 [[X]], [[TMP3]]
; CHECK-NEXT: ret i1 [[R]]
;
%x = xor i8 %x_in, 123
%neg_y = sub i8 0, %y
%nmask0 = xor i8 %y, %neg_y
%notmask = select i1 %cond, i8 %nmask0, i8 -8
%and = and i8 %x, %notmask
%r = icmp eq i8 %and, 0
ret i1 %r
}

define i1 @src_is_notmask_shl_fail_multiuse_invert(i8 %x_in, i8 %y, i1 %cond) {
; CHECK-LABEL: @src_is_notmask_shl_fail_multiuse_invert(
; CHECK-NEXT: [[X:%.*]] = xor i8 [[X_IN:%.*]], 122
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