[llvm-commits] [llvm] r138722 - in /llvm/trunk: lib/Analysis/ConstantFolding.cpp lib/Transforms/InstCombine/InstCombineCasts.cpp test/Transforms/InstCombine/cast.ll

[Rotem, Nadav]

Hi Duncan, 

I attached a patch to fix the MMX type issue. I am still not sure about the legality of casting vectors to integers, as defined in isEliminableCastPair. 

Thanks,
Nadav



-----Original Message-----
From: llvm-commits-bounces at cs.uiuc.edu [mailto:llvm-commits-bounces at cs.uiuc.edu] On Behalf Of Duncan Sands
Sent: Sunday, August 28, 2011 15:07
To: llvm-commits at cs.uiuc.edu
Subject: Re: [llvm-commits] [llvm] r138722 - in /llvm/trunk: lib/Analysis/ConstantFolding.cpp lib/Transforms/InstCombine/InstCombineCasts.cpp test/Transforms/InstCombine/cast.ll

Hi Nadav,

> Bitcasts are transitive. Bitcast-Bitcast-X becomes Bitcast-X.

sadly this is not true because you are only allowed to bitcast an mmx type
to and from a vector type, but you can bitcast vector to and from integers
etc.

> +  // Bitcast of Bitcast can be done using a single cast.
> +  ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
> +  if (CE&&  CE->getOpcode() == Instruction::BitCast) {
> +    return ConstantExpr::getBitCast(CE->getOperand(0), DestTy);
> +  }

No need for curly brackets {}.

> +  // Bitcasts are transitive.
> +  if (BitCastInst* BSrc = dyn_cast<BitCastInst>(Src)) {
> +    return CastInst::Create(Instruction::BitCast, BSrc->getOperand(0), DestTy);
> +  }

Likewise.  Also, this could be:
   if (isa<BitCastInst>(Src))
     return CastInst::Create(Instruction::BitCast, Src->getOperand(0), DestTy);
Also, shouldn't you create the cast using instcombine's builder?

Ciao, Duncan.
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