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

[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] New: Generation of MAX_EXPRs and MIN_EXPRs missed by phiopt

[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)
{
bb 2:
  if (a_2  32767) goto L3; else goto L1;

L1:;
  if (a_2  -32768) goto L2; else goto L3;

L2:;

  # a_1 = PHI 32767(2), a_2(3), -32768(4);
L3:;
  retval = a_1;
  return retval;

}

;; Function minmax_wrong (minmax_wrong)

Removing basic block 6
minmax_wrong (a)
{
bb 2:
  if (a_3  32767) goto L6; else goto L1;

L1:;
  if (a_3  -32768) goto L3; else goto L6;

  # a_9 = PHI a_3(3), 32767(2);
L6:;

  # a_2 = PHI a_9(4), -32768(3);
L3:;
  retval = a_2;
  return retval;

}
-

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)
{
bb 2:
  a_7 = MAX_EXPR -32768, a_2;
  a_8 = MIN_EXPR a_7, 32767;
  retval = a_8;
  return retval;

}

;; Function minmax_wrong (minmax_wrong)

minmax_wrong (a)
{
bb 2:
  if (a_3  32767) goto L6; else goto L1;

L1:;
  if (a_3  -32768) goto L3; else goto L6;

  # a_9 = PHI a_3(3), 32767(2);
L6:;

  # a_2 = PHI a_9(4), -32768(3);
L3:;
  retval = a_2;
  return retval;

}
-


-- 
   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

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

[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=12378action=view)
Source code of the example


-- 


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