[Bug tree-optimization/29333] Jump threading getting in the way of PHI-OPT

2006-10-05 Thread roberto dot costa at st dot com 


--- Comment #3 from roberto dot costa at st dot com  2006-10-05 08:15 
---
I tested what happens if the first PHI-OPT pass is moved right before the first
VRP pass in gcc/passes.c

It looks like PHI-OPT should be run both before and after VRP and DOM.
The example reported shows that, when PHI-OPT is run after VRP and DOM, it
misses some MAX_EXPR and MIN_EXPR generation.
gcc/testsuite/gcc.dg/tree-ssa/phi-opt-5.c shows that, when PHI-OPT anticipates
VRP and DOM, it misses some MAX_EXPR and MIN_EXPR generation as well.

Should an additional PHI-OPT pass be added before VRP and DOM?
(In this case, a few testsuite examples should also be changed in order to
consider what happens after PHI-OPT2 instead of PHI-OPT1)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29333

[Bug tree-optimization/29333] Generation of MAX_EXPRs and MIN_EXPRs missed by phiopt

2006-10-03 Thread roberto dot costa at st dot com 


--- Comment #1 from roberto dot costa at st dot com  2006-10-03 16:05 
---
Created an attachment (id=12378)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=12378&action=view)
Source code of the example


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29333

[Bug tree-optimization/29333] New: Generation of MAX_EXPRs and MIN_EXPRs missed by phiopt

2006-10-03 Thread roberto dot costa at st dot com 
There are cases in which phiopt doesn't recognize MAX_EXPRs or MIN_EXPRs
patterns.
In particular, source codes that look very similar at first sight may induce
phiopt to behave differently.

Let's consider the following two functions:

-
int minmax_correct(int a)
{
if (a > 32767) a = 32767;
else if (a < -32768) a = -32768;

return a;
}

int minmax_wrong(int a)
{
if (a > 32767) a = 32767;
if (a < -32768) a = -32768;

return a;
}
-

MIN_EXPRs and MAX_EXPRs are generated for the first function, but not for the
second.

Here is the contents of trace file minmax.c.042t.phicprop1:

-
;; Function minmax_correct (minmax_correct)

minmax_correct (a)
{
:
  if (a_2 > 32767) goto ; else goto ;

:;
  if (a_2 < -32768) goto ; else goto ;

:;

  # a_1 = PHI <32767(2), a_2(3), -32768(4)>;
:;
   = a_1;
  return ;

}

;; Function minmax_wrong (minmax_wrong)

Removing basic block 6
minmax_wrong (a)
{
:
  if (a_3 > 32767) goto ; else goto ;

:;
  if (a_3 < -32768) goto ; else goto ;

  # a_9 = PHI ;
:;

  # a_2 = PHI ;
:;
   = a_2;
  return ;

}
-

And here is minmax.c.043t.phiopt1:

-
;; Function minmax_correct (minmax_correct)

Removing basic block 4
Removing basic block 3
Merging blocks 2 and 5
minmax_correct (a)
{
:
  a_7 = MAX_EXPR <-32768, a_2>;
  a_8 = MIN_EXPR ;
   = a_8;
  return ;

}

;; Function minmax_wrong (minmax_wrong)

minmax_wrong (a)
{
:
  if (a_3 > 32767) goto ; else goto ;

:;
  if (a_3 < -32768) goto ; else goto ;

  # a_9 = PHI ;
:;

  # a_2 = PHI ;
:;
   = a_2;
  return ;

}
-


-- 
   Summary: Generation of MAX_EXPRs and MIN_EXPRs missed by phiopt
   Product: gcc
   Version: 4.2.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: roberto dot costa at st dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29333