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[InstCombine] fold (icmp eq/ne (and (shl -1, X), Y), 0) -> (icmp eq/ne (lshr Y, X), 0) #84691

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[InstCombine] fold (icmp eq/ne (and (shl -1, X), Y), 0) -> (icmp eq/ne (lshr Y, X), 0) #84691

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a426712
[InstCombine] Tests for `(icmp eq/ne (and (shl -1, X), Y), 0)` -> `(i…
goldsteinn Mar 10, 2024
65ea9f8
[InstCombine] fold `(icmp eq/ne (and (shl -1, X), Y), 0)` -> `(icmp e…
goldsteinn Mar 10, 2024
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11 changes: 11 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1962,6 +1962,17 @@ Instruction *InstCombinerImpl::foldICmpAndConstant(ICmpInst &Cmp,
return BinaryOperator::CreateAnd(TruncY, X);
}

// (icmp eq/ne (and (shl -1, X), Y), 0)
// -> (icmp eq/ne (lshr Y, X), 0)
// We could technically handle any C == 0 or (C < 0 && isOdd(C)) but it seems
// highly unlikely the non-zero case will ever show up in code.
if (C.isZero() &&
match(And, m_OneUse(m_c_And(m_OneUse(m_Shl(m_AllOnes(), m_Value(X))),
m_Value(Y))))) {
Value *LShr = Builder.CreateLShr(Y, X);
return new ICmpInst(Pred, LShr, Constant::getNullValue(LShr->getType()));
}

return nullptr;
}

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86 changes: 86 additions & 0 deletions llvm/test/Transforms/InstCombine/icmp-and-shift.ll
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Expand Up @@ -520,3 +520,89 @@ define i1 @slt_and_shl_one(i8 %x, i8 %y) {
%cmp = icmp slt i8 %and, %pow2
ret i1 %cmp
}

define i1 @fold_eq_lhs(i8 %x, i8 %y) {
; CHECK-LABEL: @fold_eq_lhs(
; CHECK-NEXT: [[AND:%.*]] = lshr i8 [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[AND]], 0
; CHECK-NEXT: ret i1 [[R]]
;
%shl = shl i8 -1, %x
%and = and i8 %shl, %y
%r = icmp eq i8 %and, 0
ret i1 %r
}

define i1 @fold_eq_lhs_fail_eq_nonzero(i8 %x, i8 %y) {
; CHECK-LABEL: @fold_eq_lhs_fail_eq_nonzero(
; CHECK-NEXT: [[SHL:%.*]] = shl nsw i8 -1, [[X:%.*]]
; CHECK-NEXT: [[AND:%.*]] = and i8 [[SHL]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[AND]], 1
; CHECK-NEXT: ret i1 [[R]]
;
%shl = shl i8 -1, %x
%and = and i8 %shl, %y
%r = icmp eq i8 %and, 1
ret i1 %r
}

define i1 @fold_eq_lhs_fail_multiuse_shl(i8 %x, i8 %y) {
; CHECK-LABEL: @fold_eq_lhs_fail_multiuse_shl(
; CHECK-NEXT: [[SHL:%.*]] = shl nsw i8 -1, [[X:%.*]]
; CHECK-NEXT: call void @use(i8 [[SHL]])
; CHECK-NEXT: [[AND:%.*]] = and i8 [[SHL]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[AND]], 0
; CHECK-NEXT: ret i1 [[R]]
;
%shl = shl i8 -1, %x
call void @use(i8 %shl)
%and = and i8 %shl, %y
%r = icmp eq i8 %and, 0
ret i1 %r
}

define i1 @fold_ne_rhs(i8 %x, i8 %yy) {
; CHECK-LABEL: @fold_ne_rhs(
; CHECK-NEXT: [[Y:%.*]] = xor i8 [[YY:%.*]], 123
; CHECK-NEXT: [[AND:%.*]] = lshr i8 [[Y]], [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = icmp ne i8 [[AND]], 0
; CHECK-NEXT: ret i1 [[R]]
;
%y = xor i8 %yy, 123
%shl = shl i8 -1, %x
%and = and i8 %y, %shl
%r = icmp ne i8 %and, 0
ret i1 %r
}

define i1 @fold_ne_rhs_fail_multiuse_and(i8 %x, i8 %yy) {
; CHECK-LABEL: @fold_ne_rhs_fail_multiuse_and(
; CHECK-NEXT: [[Y:%.*]] = xor i8 [[YY:%.*]], 123
; CHECK-NEXT: [[SHL:%.*]] = shl nsw i8 -1, [[X:%.*]]
; CHECK-NEXT: [[AND:%.*]] = and i8 [[Y]], [[SHL]]
; CHECK-NEXT: call void @use(i8 [[AND]])
; CHECK-NEXT: [[R:%.*]] = icmp ne i8 [[AND]], 0
; CHECK-NEXT: ret i1 [[R]]
;
%y = xor i8 %yy, 123
%shl = shl i8 -1, %x
%and = and i8 %y, %shl
call void @use(i8 %and)
%r = icmp ne i8 %and, 0
ret i1 %r
}

define i1 @fold_ne_rhs_fail_shift_not_1s(i8 %x, i8 %yy) {
; CHECK-LABEL: @fold_ne_rhs_fail_shift_not_1s(
; CHECK-NEXT: [[Y:%.*]] = xor i8 [[YY:%.*]], 122
; CHECK-NEXT: [[SHL:%.*]] = shl i8 -2, [[X:%.*]]
; CHECK-NEXT: [[AND:%.*]] = and i8 [[Y]], [[SHL]]
; CHECK-NEXT: [[R:%.*]] = icmp ne i8 [[AND]], 0
; CHECK-NEXT: ret i1 [[R]]
;
%y = xor i8 %yy, 123
%shl = shl i8 -2, %x
%and = and i8 %y, %shl
%r = icmp ne i8 %and, 0
ret i1 %r
}