On Tue, Jan 14, 2014 at 7:14 AM, Felix Yang <fei.yang0...@gmail.com> wrote: > Hi Sterling, > > The xtensa backend uses register windows, and we need to define > LOCAL_REGNO for it.
Hi Felix, How does this change the produced code? In particular, please identify a problem this patch is solving. I know that the documentation for the macro says to define it if you have register windows, but things aren't that straightforward. The original register windowing support in GCC went in to support Sparc and, iirc, Intel i960. There are subtle differences between the two ISAs that aren't entirely captured in the GCC infrastructure. Note that in Sparc the window isn't modified until the save and restore instructions are executed, whereas in Xtensa, the save and restores happen combined with call and return. All of this makes for very subtle data-flow issues around certain registers--in particular, a8 (which functions as both an argument register and the frame pointer.) Passing gcc/torture/... isn't enough to establish that this works. It needs a full set of ABI tests to be established as correct. What we have there works perfectly well. Your patch may indeed improve the generated code, or be more correct, but please identify the problem you are solving and show how this patch improves things. Thanks, Sterling
