[valgrind] [Bug 384676] VEX AMD64 backend should list more real registers as available for the register allocator

[Ivo Raisr]

https://bugs.kde.org/show_bug.cgi?id=384676

Ivo Raisr  changed:

   What|Removed |Added

 Resolution|--- |WONTFIX
 Status|ASSIGNED|RESOLVED

--- Comment #4 from Ivo Raisr  ---
Even after bug 384987 has been fixed, the situation did not improve much.

Running Memcheck on perf/bz2 [number of instructions]:
baseline: total: 44,936,961,809; reg alloc: 168,848,160; ratio: 15.3
patched:  total: 44,933,693,157; reg alloc: 177,659,739; ratio: 15.3

Running Memcheck on perf/tinycc:
baseline: total: 3,938,404,232; reg alloc: 121,447,931; ratio 16.2
patched:  total: 3,939,903,162; reg alloc: 127,930,047; ratio 16.2

With perf/bz2, there is only a very minor improvement. With perf/tinycc there
is actually a very minor deterioration.

I am abandoning this bug for good.

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[valgrind] [Bug 384676] VEX AMD64 backend should list more real registers as available for the register allocator

[Julian Seward]

https://bugs.kde.org/show_bug.cgi?id=384676

Julian Seward  changed:

   What|Removed |Added

 CC||jsew...@acm.org

--- Comment #3 from Julian Seward  ---
Yes, that sounds pretty similar to what I found too.

We maybe should re-evaluate this when the control-flow-diamond
stuff comes to life, because it might be the case that that allows
us to have longer sequences of instructions between helper calls
and so there is more demand for registers.

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[valgrind] [Bug 384676] VEX AMD64 backend should list more real registers as available for the register allocator

[Ivo Raisr]

https://bugs.kde.org/show_bug.cgi?id=384676

--- Comment #2 from Ivo Raisr  ---
Unfortunately performance measurements do not confirm this as a good idea.

Measuring Memcheck on perf/bz2, instruction count:
v3 baseline: 45,110 M total; 168 M register allocator
v3 patched:  45,123 M total; 176 M register allocator
v2 baseline: 45,190 M total; 209 M register allocator
v2 patched:  45,266 M total; 220 M register allocator

Measuring Memcheck on tinycc, instruction count:
v3 baseline: 4,155,471 k total; 86,438 k register allocator
v3 patched:  4,155,207 k total; 91,193 k register allocator

I'd conclude that although two more registers are available to the register
allocator, it does not help because:
- they are caller saved registers
- register allocator needs to iterate over more registers

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[valgrind] [Bug 384676] VEX AMD64 backend should list more real registers as available for the register allocator

[Ivo Raisr]

https://bugs.kde.org/show_bug.cgi?id=384676

Ivo Raisr  changed:

   What|Removed |Added

   See Also||https://bugs.kde.org/show_b
   ||ug.cgi?id=384584

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[valgrind] [Bug 384676] VEX AMD64 backend should list more real registers as available for the register allocator

[Ivo Raisr]

https://bugs.kde.org/show_bug.cgi?id=384676

Ivo Raisr  changed:

   What|Removed |Added

 CC||iv...@ivosh.net

--- Comment #1 from Ivo Raisr  ---
Created attachment 107840
  --> https://bugs.kde.org/attachment.cgi?id=107840=edit
patch

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[valgrind] [Bug 384676] VEX AMD64 backend should list more real registers as available for the register allocator

[Ivo Raisr]

https://bugs.kde.org/show_bug.cgi?id=384676

Ivo Raisr  changed:

   What|Removed |Added

 Ever confirmed|0   |1
   Assignee|jsew...@acm.org |iv...@ivosh.net
 Status|UNCONFIRMED |ASSIGNED

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