This is the mail archive of the gcc-bugs@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

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


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


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]