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Re: [PATCH] Fix PR37053: Move tweaks of commutative precedence to target hook


Peter Bergner wrote:
On Fri, 2009-06-26 at 18:15 +0400, Maxim Kuvyrkov wrote:
The attached patch fixes PR37053 (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37053#c5).

The problem was introduced by patch for PR28690 (http://gcc.gnu.org/ml/gcc-patches/2006-12/msg00268.html, rtlanal.c hunk); this hunk causes ICE on m68k (and, possibly, other) architectures.
[snip]
My first impulse was to remove the pointer tweak; but, well, if PowerPC really benefits from it,

I will say we worked for a long time coming up with the patch we did so that it didn't affect other arches. In particular, HJ ran a lot of performance tests to make sure it didn't degrade performance on x86.

I cannot say I like Maxim's patch and he knows, but unfortunately, m68k apparently implements 2-address arithmetic in a different way than x86 (or with other constraint) and we're talking about a lot of ICEs there. :-(


Another possibility, which you would have to try on PowerPC, could be to limit the change of precedence to before reload. That would be a simpler patch and one that does not risk slowing down the compiler that tiny 0.1% that sums up quickly. But it would also be pretty magical...

Paolo


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