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Instcombine zext(trunc(x) & mask) to x&mask, even if the trunc has

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multiple users.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73656 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-06-17 23:17:05 +00:00
parent a23d2c1262
commit a392c788be
2 changed files with 37 additions and 0 deletions
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14
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -8564,6 +8564,20 @@ Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
}
}
// zext(trunc(t) & C) -> (t & C) if C is a mask.
if (SrcI && SrcI->getOpcode() == Instruction::And && SrcI->hasOneUse())
if (ConstantInt *C = dyn_cast<ConstantInt>(SrcI->getOperand(1)))
if (TruncInst *TI = dyn_cast<TruncInst>(SrcI->getOperand(0))) {
Value *TI0 = TI->getOperand(0);
if (TI0->getType() == CI.getType()) {
unsigned TO = C->getValue().countTrailingOnes();
if (APIntOps::isMask(TO, C->getValue()))
return
BinaryOperator::Create(Instruction::And, TI0,
ConstantExpr::getZExt(C, CI.getType()));
}
}
return 0;
}

23
test/Transforms/InstCombine/trunc-mask-ext.ll Normal file
View File

@ -0,0 +1,23 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis > %t
; RUN: not grep zext %t
; RUN: not grep sext %t
; Instcombine should be able to eliminate both ext casts.
declare void @use(i32)
define i64 @foo(i64 %a) {
%b = trunc i64 %a to i32
%c = and i32 %b, 15
%d = zext i32 %c to i64
call void @use(i32 %b)
ret i64 %d
}
define i64 @bar(i64 %a) {
%b = trunc i64 %a to i32
%c = shl i32 %b, 4
%q = ashr i32 %c, 4
%d = sext i32 %q to i64
call void @use(i32 %b)
ret i64 %d
}