Skip to content

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

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
goldsteinn wants to merge 2 commits into from
Closed

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

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
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
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
11 changes: 11 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View file
Open in desktop
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;
}

Expand Down
86 changes: 86 additions & 0 deletions llvm/test/Transforms/InstCombine/icmp-and-shift.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
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
}