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[InstCombine] Fold ((C1-zext(X)) & C2) -> zext((C1-X) & C2)

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This is valid if C2 fits within the bitwidth of X thanks to two's
complement modulo arithmetic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292179 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2017-01-17 00:45:57 +00:00
parent 3802a656d3
commit 4b66daa8cc
2 changed files with 26 additions and 0 deletions
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15
lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
View File

@ -1331,6 +1331,21 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
if (Value *V = FoldLogicalPlusAnd(Op0LHS, Op0RHS, AndRHS, true, I))
return BinaryOperator::CreateAnd(V, AndRHS);
// ((C1-zext(X)) & C2) -> zext((C1-X) & C2) if C2 fits in the bitwidth
// of X.
if (auto *ZI = dyn_cast<ZExtInst>(Op0RHS)) {
auto *X = ZI->getOperand(0);
ConstantInt *C1;
if (match(Op0LHS, m_ConstantInt(C1)) &&
AndRHSMask.isIntN(X->getType()->getScalarSizeInBits())) {
auto *TruncC1 = ConstantExpr::getTrunc(C1, X->getType());
auto *Sub = Builder->CreateSub(TruncC1, X);
auto *TruncC2 = ConstantExpr::getTrunc(AndRHS, X->getType());
auto *And = Builder->CreateAnd(Sub, TruncC2);
return new ZExtInst(And, I.getType());
}
}
// -x & 1 -> x & 1
if (AndRHSMask == 1 && match(Op0LHS, m_Zero()))
return BinaryOperator::CreateAnd(Op0RHS, AndRHS);

11
test/Transforms/InstCombine/and.ll
View File

@ -425,3 +425,14 @@ define <2 x i32> @PR24942(<2 x i32> %x) {
ret <2 x i32> %and
}
define i64 @test35(i32 %X) {
; CHECK-LABEL: @test35(
; CHECK-NEXT: %[[sub:.*]] = sub i32 0, %X
; CHECK-NEXT: %[[and:.*]] = and i32 %[[sub]], 240
; CHECK-NEXT: %[[cst:.*]] = zext i32 %[[and]] to i64
; CHECK-NEXT: ret i64 %[[cst]]
%zext = zext i32 %X to i64
%zsub = sub i64 0, %zext
%res = and i64 %zsub, 240
ret i64 %res
}