Implemented. I'll start using them. Reid. On Mon, 2006-12-04 at 11:11 -0800, Chris Lattner wrote: > Reid, > > Most of your uses of getInferredCast fall into one of these categories: > > 1. They can only be one type of cast. > 2. They can be a [bitcast or trunc] or [bitcast or zext] or [bitcast > or sext]. > > The former should be eliminated obviously, so I want to talk about > the later. > > As a specific example, consider: > > // gep null, C is equal to C*sizeof(nullty). If nullty is > a known llvm > // type, we can statically fold this. > Constant *R = ConstantInt::get(Type::UIntTy, ElSize); > + // We know R is unsigned, Idx0 is signed because it must be > an index > + // through a sequential type (gep pointer operand) which is > always > + // signed. > + R = ConstantExpr::getInferredCast(R, false, Idx0->getType(), > true); > + R = ConstantExpr::getMul(R, Idx0); // signed multiply > + // R is a signed integer, C is the GEP pointer so -> IntToPtr > + return ConstantExpr::getCast(Instruction::IntToPtr, R, C- > >getType()); > > In this case, we know that the cast is either bitcast to uint/int or > a zext to long/ulong [1]. Because you know this, you have a 3 line > comment trying to explain what is going on, and that comment is > confusing (it talks about the types of values, when values are about > to be untyped). > > What we really want to do is talk about the possible extension > happening here. As such, I think it would be much cleaner to split > up getInferredCast into: > > ConstantExpr::getZExtOrBitCast(..) > ConstantExpr::getSExtOrBitCast(..) > ConstantExpr::getTruncOrBitCast(..) > > This would allow writing this code as: > > // gep null, C is equal to C*sizeof(nullty). If nullty is > a known llvm > // type, we can statically fold this. > Constant *R = ConstantInt::get(Type::UIntTy, ElSize); > + R = ConstantExpr::getZExtOrBitCast(R, Idx0->getType()); > + R = ConstantExpr::getMul(R, Idx0); // signed multiply > + // R is a signed integer, C is the GEP pointer so -> IntToPtr > + return ConstantExpr::getCast(Instruction::IntToPtr, R, C- > >getType()); > > The need for the comment goes away. Even *better*, the method can > assert that the types make sense for this (e.g. a trunc isn't from > smaller to larger) as opposed to the totally unconstrained > getInferredCast. > > This makes the code a) more self documenting as to what is going on > and b) much more strict about checking itself. What do you think? > Would this allow us to completely eliminate getInferredCast? > > -Chris > > [1]. As an aside, if you relaxed the type constraints of GEP indices, > this gets much messier. > _______________________________________________ > llvm-commits mailing list > llvm-commits@cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
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