r255760 - in /trunk/gcc: ChangeLog config/i386/...

[trippels@gcc.gnu.org]

Author: trippels
Date: Sun Dec 17 12:01:25 2017
New Revision: 255760

URL: https://gcc.gnu.org/viewcvs?rev=255760&root=gcc&view=rev
Log:
Correct imul (r64) latency for modern Intel CPUs

Since Sandybridge the 64bit multiplication latency is three cycles, not
four. So update the costs to reflect reality.

	* x86-tune-costs.h (skylake_cost, core_cost): Decrease r64 multiply
	latencies.

	* gcc.target/i386/wmul-3.c: New test.

Added:
    trunk/gcc/testsuite/gcc.target/i386/wmul-3.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config/i386/x86-tune-costs.h
    trunk/gcc/testsuite/ChangeLog