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Generalize this transform, using MaskedValueIsZero, allowing us to compile: 

struct S { unsigned int i : 6, j : 11, k : 15; } b;
void plus3 (unsigned int x) { b.k += x; }

To:

plus3:
        mov %EAX, DWORD PTR [%ESP + 4]
        shl %EAX, 17
        add DWORD PTR [b], %EAX
        ret

instead of:

plus3:
        mov %EAX, DWORD PTR [%ESP + 4]
        shl %EAX, 17
        mov %ECX, DWORD PTR [b]
        add %EAX, %ECX
        and %EAX, -131072
        and %ECX, 131071
        or %ECX, %EAX
        mov DWORD PTR [b], %ECX
        ret

llvm-svn: 23384
This commit is contained in:
Chris Lattner 2005-09-18 06:02:59 +00:00
parent 4ebc8ab4e0
commit 01f56c68e9
1 changed files with 21 additions and 14 deletions
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35
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -225,7 +225,6 @@ namespace {
Value *FoldLogicalPlusAnd(Value *LHS, Value *RHS, ConstantIntegral *Mask,
bool isSub, Instruction &I);
Instruction *InsertRangeTest(Value *V, Constant *Lo, Constant *Hi,
bool Inside, Instruction &IB);
};
@ -1995,19 +1994,27 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
return BinaryOperator::createAnd(A, ConstantExpr::getOr(C1, C2));
// if A == (add B, C3) or B == (add A, C4)
ConstantInt *C3 = 0;
Value *V = 0;
if ((match(A, m_Add(m_Value(V), m_ConstantInt(C3))) && V == B ||
match(B, m_Add(m_Value(V), m_ConstantInt(C3))) && V == A)) {
if (V == A) std::swap(C1, C2);
// We have: ((V + C3) & C1) | (V & C2)
// if C2 = ~C1 and (C3 & C2) == 0 and C2 is 0+1+
if (C1 == ConstantExpr::getNot(C2) &&
ConstantExpr::getAnd(C3, C2)->isNullValue() &&
(C2->getRawValue() & (C2->getRawValue()+1)) == 0) {
// Return V+C3.
return ReplaceInstUsesWith(I, V == A ? B : A);
// If we have: ((V + N) & C1) | (V & C2)
// .. and C2 = ~C1 and C2 is 0+1+ and (N & C2) == 0
// replace with V+N.
if (C1 == ConstantExpr::getNot(C2)) {
Value *V1, *V2;
if ((C2->getRawValue() & (C2->getRawValue()+1)) == 0 && // C2 == 0+1+
match(A, m_Add(m_Value(V1), m_Value(V2)))) {
// Add commutes, try both ways.
if (V1 == B && MaskedValueIsZero(V2, C2))
return ReplaceInstUsesWith(I, A);
if (V2 == B && MaskedValueIsZero(V1, C2))
return ReplaceInstUsesWith(I, A);
}
// Or commutes, try both ways.
if ((C1->getRawValue() & (C1->getRawValue()+1)) == 0 &&
match(B, m_Add(m_Value(V1), m_Value(V2)))) {
// Add commutes, try both ways.
if (V1 == A && MaskedValueIsZero(V2, C1))
return ReplaceInstUsesWith(I, B);
if (V2 == A && MaskedValueIsZero(V1, C1))
return ReplaceInstUsesWith(I, B);
}
}
}