[llvm-commits] [llvm] r60608 - in /llvm/trunk: lib/Target/X86/X86ISelLowering.cpp lib/Target/X86/X86Subtarget.cpp lib/Transforms/Scalar/LoopStrengthReduce.cpp test/CodeGen/X86/loop-strength-reduce-2.ll test/CodeGen/X86/loop-strength-reduce-3.ll test/CodeGen/X86/loop-strength-reduce.ll

[Dale Johannesen]

On Dec 5, 2008, at 2:01 PMPST, Anton Korobeynikov wrote:

> Hi, Dale
>
>>
>> +/// True if accessing the GV requires a register.  This is a
>> superset of the
>> +/// cases where GVRequiresExtraLoad is true.  Some variations of
>> PIC require
>> +/// a register, but not an extra load.
>> +bool X86Subtarget::GVRequiresRegister(const GlobalValue *GV,
>> +                                       const TargetMachine& TM,
>> +                                       bool isDirectCall) const
>> +{
>> +  if (GVRequiresExtraLoad(GV, TM, isDirectCall))
>> +    return true;
>> +  // Code below here need only consider cases where
>> GVRequiresExtraLoad
>> +  // returns false.
>> +  if (TM.getRelocationModel() == Reloc::PIC_)
>> +    return !isDirectCall &&
>> +      (GV->hasInternalLinkage() || GV->hasExternalLinkage());
> I don't understand this. Why only internal and external linkage?

All the others are already handled by GVRequiresExtraLoad.  (At least  
for Darwin.)

> Actually for PIC on Linux (32 bit only) access to every symbols,
> except ones with internal linkage or hidden visibility requires a GOT
> register access. There was even special hook inside
> X86ISelLowering.cpp (incomplete in general, but usable -
> CallRequiresGOTPtrInReg() and another one around) for this sort of
> thing. Please consider using it.

This applies to data objects, not calls.  The rules are fairly  
different for calls and data, and I'm not sure commonality is useful.
The hook I'm interested in fixing is isLegalAddressingMode, which  
isn't calling into the Linux function you mention.

> We've just ended with 3 hooks used
> for more or less similar stuff.
>
> It will be nice to have all this in one place and in consistent  
> state...
>
> ---
> With best regards, Anton Korobeynikov
> Faculty of Mathematics and Mechanics, Saint Petersburg State  
> University
>
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