https://bugs.kde.org/show_bug.cgi?id=384987
Bug ID: 384987
Summary: VEX register allocator: allocate caller-save registers
for short lived vregs
Product: valgrind
Version: 3.14 SVN
Platform: Compiled Sources
OS: Linux
Status: UNCONFIRMED
Severity: normal
Priority: NOR
Component: vex
Assignee: jsew...@acm.org
Reporter: iv...@ivosh.net
Target Milestone: ---
This is a performance improvement based on Peter Bergner's suggestion:
Allocate caller-saved registers for short lived vregs and callee-save registers
for vregs which span accross helper calls.
This idea is quite simple but MOV coalescing went in the way.
The first patch enhances MOV coalescing so it keeps better track of what
registers form the coalescing chain. The second patch actually changes
find_free_rreg().
With just a minor additional complexity, we get more compact generated code.
This not only helps for better performance; it should also help with i-cache
misses.
Measuring instruction count, running inner Memcheck:
perf/bz2:
vanilla: 45,112,349,784 total; reg alloc 165,978,807; ratio 15.5 (97,397
-> 1,506,163)
coalesce only: 45,120,691,777 total; reg alloc 167,035,575; ratio 15.5 (97,610
-> 1,509,396)
both patches: 44,943,765,809 total; reg alloc 167,403,237; ratio 15.3 (97,607
-> 1,493,722)
/bin/true:
vanilla: 3,514,906,884 total; reg alloc 60,779,126
coalesce only: 3,506,029,832 total; reg alloc 61,242,900
both patches: 3,503,495,437 total; reg alloc 61,395,160
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