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my instcombine transformations to make extension elimination more

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aggressive changed the canonical form from sext(trunc(x)) to ashr(lshr(x)),
make sure to transform a couple more things into that canonical form,
and catch a case where we missed turning zext/shl/ashr into a single sext.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93787 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2010-01-18 22:19:16 +00:00
parent 2122f69c02
commit cd5adbbc0c
3 changed files with 47 additions and 11 deletions
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13
lib/Transforms/InstCombine/InstCombineCasts.cpp
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@@ -955,6 +955,19 @@ Instruction *InstCombiner::visitSExt(SExtInst &CI) {
ShAmt);
}
// If this input is a trunc from our destination, then turn sext(trunc(x))
// into shifts.
if (TruncInst *TI = dyn_cast<TruncInst>(Src))
if (TI->hasOneUse() && TI->getOperand(0)->getType() == DestTy) {
uint32_t SrcBitSize = SrcTy->getScalarSizeInBits();
uint32_t DestBitSize = DestTy->getScalarSizeInBits();
// We need to emit a shl + ashr to do the sign extend.
Value *ShAmt = ConstantInt::get(DestTy, DestBitSize-SrcBitSize);
Value *Res = Builder->CreateShl(TI->getOperand(0), ShAmt, "sext");
return BinaryOperator::CreateAShr(Res, ShAmt);
}
// If the input is a shl/ashr pair of a same constant, then this is a sign
// extension from a smaller value. If we could trust arbitrary bitwidth
// integers, we could turn this into a truncate to the smaller bit and then