On Apr 15, 2011, at 4:38 PM, Maxim Kuvyrkov wrote: > On Apr 15, 2011, at 3:34 PM, Eric Botcazou wrote: > >>> The problem this patch fixes is that combine_simplify_rtx() prefers to >>> return an expression (say, <xor (a) (b)>) even when a comparison is >>> prefered (say, <neq (xor (a) (b)) 0>). Expressions are not recognized as >>> valid conditions of if_then_else for most targets, so combiner misses a >>> potential optimization. This patch makes combine_simplify_rtx() aware of >>> the context it was invoked in, and, when appropriate, does not discourage >>> it from returning a conditional. >> >> Btw, this is very likely also valid for targets with STORE_FLAG_VALUE == -1 >> so >> the same IN_COND short-circuit would need to be added a few lines below in >> combine_simplify_rtx. But this would need to be tested. Do you happen to >> have access to such a target, e.g. m68k? > > Hm, I didn't notice that one, thanks! I have access to m68k (ColdFire, tbp) > and will test this change there before committing.
I've successfully tested the following trivial patch on m68k-linux (cross-compiler, gcc, g++ and libstdc++ testsuites). Checked in as obvious. -- Maxim Kuvyrkov Mentor Graphics / CodeSourcery
fsf-gcc-combine-fix-1.ChangeLog
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fsf-gcc-combine-fix-1.patch
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