[llvm] r211040 - Fix illegal relocations in X86FastISel

[Louis Gerbarg]

Per our discussions on IRC I committed a patch with improved comments explaining what is going on in case anyone ever has need to bring this into fast isel instead of just bailing since it is an edge case: r211052.

> On Jun 16, 2014, at 10:52 AM, Eric Christopher <echristo at gmail.com> wrote:
> 
> On Mon, Jun 16, 2014 at 10:35 AM, Louis Gerbarg <lgg at apple.com> wrote:
>> Author: louis
>> Date: Mon Jun 16 12:35:40 2014
>> New Revision: 211040
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=211040&view=rev
>> Log:
>> Fix illegal relocations in X86FastISel
>> 
>> On x86_86  the lea instruction can only use a 32 bit immediate value. When
>> the code is compiled statically the RIP register is not used, meaning the
>> immediate is all that can be used for the relocation, which is not sufficient
>> in the case of targets more than +/- 2GB away. This patch bails out of fast
>> isel in those cases and reverts to DAG which does the right thing.
>> 
>> Test case included.
> 
> Some questions below:
> 
>>   // Materialize addresses with LEA instructions.
>>   if (isa<GlobalValue>(C)) {
>> +    //LEA can only handle 32 bit immediates
>> +    if (TM.getRelocationModel() == Reloc::Static && Subtarget->is64Bit())
>> +      return false;
>> +
>> 
> 
> Couldn't we lock down this check a bit more or handle the case?
> 
>> ==============================================================================
>> --- llvm/trunk/test/DebugInfo/X86/debug-loc-asan.ll (original)
>> +++ llvm/trunk/test/DebugInfo/X86/debug-loc-asan.ll Mon Jun 16 12:35:40 2014
>> @@ -10,10 +10,10 @@
>> ; with "clang++ -S -emit-llvm -fsanitize=address -O0 -g test.cc"
>> 
>> ; First, argument variable "y" resides in %rdi:
>> -; CHECK: DEBUG_VALUE: bar:y <- RDI
>> +; CHECK: DEBUG_VALUE: bar:y <- RDX
>> 
> 
> The comment says rdi, the code says rdx. :)
> 
> Did you verify it's actually in rdx now? If so, could you update it.

Also cleaned this comment up in r211052.

Louis
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