[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 3:52 PMPST, Evan Cheng wrote:
>> 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.)
>
> That doesn't sound right. For Darwin x86 32-bit PIC, all data load
> requires the pic base register. This has nothing to do with whether a
> stub is needed.

What is it that doesn't sound right?  You're quite right this has  
nothing to do with stubs, why do you think it does?

There is a difference between requiring the pic register and requiring  
an extra
load; the former was not being modelled.  Externals are referenced via
	leal	L_x5$non_lazy_ptr-"L00000000001$pb"(%ebx), %eax
	movl	(%eax), %eax         << loading address
	movl	(%eax), %eax         << loading value
This case returns true from GVRequiresExtraLoad.

Statics and globals are referenced via
	leal	_x0-"L00000000001$pb"(%ebx), %eax
	movl	(%eax), %eax         << loading value
This case returns false from GVRequiresExtraLoad but true from  
GVRequiresRegister.