[Bug rtl-optimization/20242] New: Pessimizing effects of defining EXTRA_MEMORY_CONSTRAINT

[Bug rtl-optimization/20242] New: Pessimizing effects of defining EXTRA_MEMORY_CONSTRAINT

[hp at gcc dot gnu dot org]

In some large functions, where all hardware registers are "used
up" and some pseudo-register need to be allocated on stack,
EXTRA_MEMORY_CONSTRAINT will have a pessimizing effect.  Without
further analysis, it seems that it causes pseudo-registers to be
committed ("too devoted") to memory with no apparent re-use of
registers, if any free one is found later on (perhaps as part of
reload inheritance).  I compared LAST_UPDATED: "Sun Feb 27 17:43:10
UTC 2005" without (0) and with (1) the patch at <URL:> and also with
the patch applied except the EXTRA_MEMORY_CONSTRAINT definition
(2) (the removal of that line and the atomicity.h patch to avoid
build failure).  For ghostscript-5.50 (patched to submission for
current trunk) and the minimal input in the attachment named
test.ps, emitting png, the longest_match function (from zlib 1.1.3)
in the attached test-case (attachment bigfun.i) was part of an
execution path with similar other pessimizations observed.
Numbers are simulated schedulable cycles.  0, baseline:
495989262. 1, E_M_C: 498036429 (time-ratio vs baseline:
100.41%).  2, Q-fixes but no E_M_C was identical to baseline.

Note differences in between "baseline" and "fixed-Q-and-E_M_C"
in the generated assembly code (baseline and diff to be attached).
Compiled with "-O2 -march=v10 -mno-mul-bug-workaround".

-- 
           Summary: Pessimizing effects of defining EXTRA_MEMORY_CONSTRAINT
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P2
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hp at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: cris-axis-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20242

[Bug rtl-optimization/20242] Pessimizing effects of defining EXTRA_MEMORY_CONSTRAINT

[hp at gcc dot gnu dot org]

------- Additional Comments From hp at gcc dot gnu dot org  2005-02-28 02:52 -------
(1) Is <URL:http://gcc.gnu.org/ml/gcc-patches/2005-02/msg01769.html> and doesn't
contain the atomicity.h patch.

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20242

[Bug rtl-optimization/20242] Pessimizing effects of defining EXTRA_MEMORY_CONSTRAINT

[hp at gcc dot gnu dot org]

------- Additional Comments From hp at gcc dot gnu dot org  2005-02-28 02:56 -------
Created an attachment (id=8293)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=8293&action=view)
test.ps

Minimal ghostscript input file for noticing performance regression.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20242

[Bug rtl-optimization/20242] Pessimizing effects of defining EXTRA_MEMORY_CONSTRAINT

[hp at gcc dot gnu dot org]

------- Additional Comments From hp at gcc dot gnu dot org  2005-02-28 03:01 -------
Created an attachment (id=8294)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=8294&action=view)
bigfun.i

Test-case.

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20242

[Bug rtl-optimization/20242] Pessimizing effects of defining EXTRA_MEMORY_CONSTRAINT

[hp at gcc dot gnu dot org]

------- Additional Comments From hp at gcc dot gnu dot org  2005-02-28 03:06 -------
Created an attachment (id=8295)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=8295&action=view)
baseline

Generated code before (1) and also if *only* the EXTRA_MEMORY_CONSTRAINT is
removed.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20242

[Bug rtl-optimization/20242] Pessimizing effects of defining EXTRA_MEMORY_CONSTRAINT

[hp at gcc dot gnu dot org]

------- Additional Comments From hp at gcc dot gnu dot org  2005-02-28 03:11 -------
Created an attachment (id=8296)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=8296&action=view)
diff -up baseline.s fixed-Q-and-E_M_C.s

Diff showing regressing change in generated assembly code.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20242

[Bug rtl-optimization/20242] Pessimizing effects of defining EXTRA_MEMORY_CONSTRAINT

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2005-03-10 14:21:43
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20242