[llvm-commits] [llvm][PATCH][Review Requested] Fix failure to realign stack on x86

[Jakob Stoklund Olesen]

On Jan 18, 2012, at 9:55 AM, Gurd, Preston wrote:

> The attached one line patch corrects a problem whereby llvm was failing to generate an ANDL instruction to align the stack pointer on function entry when the required alignment was mod 16 and when stack realignment was requested.

> --- lib/Target/X86/X86RegisterInfo.cpp	(revision 148345)
> +++ lib/Target/X86/X86RegisterInfo.cpp	(working copy)
> @@ -352,7 +352,7 @@
>    const MachineFrameInfo *MFI = MF.getFrameInfo();
>    const Function *F = MF.getFunction();
>    unsigned StackAlign = TM.getFrameLowering()->getStackAlignment();
> -  bool requiresRealignment = ((MFI->getMaxAlignment() > StackAlign) ||
> +  bool requiresRealignment = ((MFI->getMaxAlignment() >= StackAlign) ||
>                                 F->hasFnAttr(Attribute::StackAlignment));
> 

I don't understand this change. Why realign the stack when it is already sufficiently aligned?

/jakob

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