[llvm-commits] [llvm] r141500 - /llvm/trunk/lib/Target/X86/X86RegisterInfo.cpp

[Cameron Zwarich]

Could this sort of thing be checked statically?

Sent from my iPhone

On Oct 8, 2011, at 1:20 PM, Jakob Stoklund Olesen <stoklund at 2pi.dk> wrote:

> Author: stoklund
> Date: Sat Oct  8 15:20:03 2011
> New Revision: 141500
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=141500&view=rev
> Log:
> Prevent potential NOREX bug.
> 
> A GR8_NOREX virtual register is created when extrating a sub_8bit_hi
> sub-register:
> 
>  %vreg2<def> = COPY %vreg1:sub_8bit_hi; GR8_NOREX:%vreg2 %GR64_ABCD:%vreg1
>  TEST8ri_NOREX %vreg2, 1, %EFLAGS<imp-def>; GR8_NOREX:%vreg2
> 
> If such a live range is ever split, its register class must not be
> inflated to GR8.  The sub-register copy can only target GR8_NOREX.
> 
> I dont have a test case for this theoretical bug.
> 
> Modified:
>    llvm/trunk/lib/Target/X86/X86RegisterInfo.cpp
> 
> Modified: llvm/trunk/lib/Target/X86/X86RegisterInfo.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86RegisterInfo.cpp?rev=141500&r1=141499&r2=141500&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/X86/X86RegisterInfo.cpp (original)
> +++ llvm/trunk/lib/Target/X86/X86RegisterInfo.cpp Sat Oct  8 15:20:03 2011
> @@ -246,6 +246,17 @@
> 
> const TargetRegisterClass*
> X86RegisterInfo::getLargestLegalSuperClass(const TargetRegisterClass *RC) const{
> +  // Don't allow super-classes of GR8_NOREX.  This class is only used after
> +  // extrating sub_8bit_hi sub-registers.  The H sub-registers cannot be copied
> +  // to the full GR8 register class in 64-bit mode, so we cannot allow the
> +  // reigster class inflation.
> +  //
> +  // The GR8_NOREX class is always used in a way that won't be constrained to a
> +  // sub-class, so sub-classes like GR8_ABCD_L are allowed to expand to the
> +  // full GR8 class.
> +  if (RC == X86::GR8_NOREXRegisterClass)
> +    return RC;
> +
>   const TargetRegisterClass *Super = RC;
>   TargetRegisterClass::sc_iterator I = RC->getSuperClasses();
>   do {
> 
> 
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