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Simplify (A & ~B) in icmp if A is a power of 2 

The transform will execute like so:
(A & ~B) == 0 --> (A & B) != 0
(A & ~B) != 0 --> (A & B) == 0

llvm-svn: 179386
This commit is contained in:
David Majnemer 2013-04-12 17:25:07 +00:00
parent 2249e9cfa8
commit 1a08accbb7
2 changed files with 35 additions and 0 deletions
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9
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -2669,6 +2669,15 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
}
{ Value *A, *B;
// Transform (A & ~B) == 0 --> (A & B) != 0
// and (A & ~B) != 0 --> (A & B) == 0
// if A is a power of 2.
if (match(Op0, m_And(m_Value(A), m_Not(m_Value(B)))) &&
match(Op1, m_Zero()) && isKnownToBeAPowerOfTwo(A) && I.isEquality())
return new ICmpInst(I.getInversePredicate(),
Builder->CreateAnd(A, B),
Op1);
// ~x < ~y --> y < x
// ~x < cst --> ~cst < x
if (match(Op0, m_Not(m_Value(A)))) {

26
llvm/test/Transforms/InstCombine/icmp.ll
View File

@ -938,3 +938,29 @@ define i1 @icmp_sub57_sge_sub20(i32 %x, i32 %y) {
%cmp = icmp sge i32 %1, %2
ret i1 %cmp
}
; CHECK: @icmp_and_shl_neg_ne_0
; CHECK-NEXT: [[SHL:%[a-z0-9]+]] = shl i32 1, %B
; CHECK-NEXT: [[AND:%[a-z0-9]+]] = and i32 [[SHL]], %A
; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp eq i32 [[AND]], 0
; CHECK-NEXT: ret i1 [[CMP]]
define i1 @icmp_and_shl_neg_ne_0(i32 %A, i32 %B) {
%neg = xor i32 %A, -1
%shl = shl i32 1, %B
%and = and i32 %shl, %neg
%cmp = icmp ne i32 %and, 0
ret i1 %cmp
}
; CHECK: @icmp_and_shl_neg_eq_0
; CHECK-NEXT: [[SHL:%[a-z0-9]+]] = shl i32 1, %B
; CHECK-NEXT: [[AND:%[a-z0-9]+]] = and i32 [[SHL]], %A
; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp ne i32 [[AND]], 0
; CHECK-NEXT: ret i1 [[CMP]]
define i1 @icmp_and_shl_neg_eq_0(i32 %A, i32 %B) {
%neg = xor i32 %A, -1
%shl = shl i32 1, %B
%and = and i32 %shl, %neg
%cmp = icmp eq i32 %and, 0
ret i1 %cmp
}