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Re: [patch] regcprop fix for PR rtl-optimization/54300


On 11/19/13 10:32, Steven Bosscher wrote:

Yes. In the GCC3 days it was important for sincos on i386, and on mk68
it used to be important for some of the funnier patterns. Not sure if
it's still useful today, though. Might be worth looking into, just to
avoid the confusion in the future.
I doubt it's changed all that much :-)


There's been confusion about this before, where people assumed
single_set really means "just one SET in this pattern". (ISTR fixing
gcse.c's hash_scan_rtx for this at some point...?). But that's not the
semantics of single_set.
Yes. And I'd expect confusion to continue :( Not sure if creating renaming to capture the actual semantics would help here.


The proper test for "just one SET" is (!multiple_sets && single_set).
At least, that's how I've always coded it...
Seems reasonable for those cases where you have to ensure there really is just one set.


jeff


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