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Re: [PATCH][GCC] Simplification of 1U << (31 - x)


Hi Jakub

As per the discussions, I have a created a bug report for the possible regression this may cause.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82454

Sudi


From: Wilco Dijkstra
Sent: Tuesday, September 26, 2017 2:20 PM
To: Sudi Das; Jakub Jelinek
Cc: Richard Biener; GCC Patches; nd; Richard Earnshaw; James Greenhalgh
Subject: Re: [PATCH][GCC] Simplification of 1U << (31 - x)
    
Jakub Jelinek wrote:

> Well, we don't want to regress performance wise on one of the most important
> primary targets.  I don't care that much if the RTL/backend work is done
> together with the patch, or as a follow-up during stage1/3, but it should be
> done, the testcases I've posted can be used as a basis of a P1 runtime
> performance regression.

It should be sufficient to file a bug about inefficient 64-bit constant expansions on
x64. I didn't see a significant difference in my benchmarking of it on x64, so I'd say
it's only a performance regression if large benchmarks regress measurably (quite
unlikely).

Wilco    

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