[Bug tree-optimization/39874] New: [4.4 regression] missing DCE

[Bug tree-optimization/39874] New: [4.4 regression] missing DCE

[alexvod at google dot com]

The following code:
void func();
void test(char *signature)
{
  char ch = signature[0];
  if (ch == 15 || ch == 3)
  {
    if (ch == 15) func();
  }
}
is compiled in suboptimal way by gcc 4.4. Check for ch==3 can be completely
eliminated since func is only called if ch==15. gcc 4.3 is able to properly
infer this and eliminate the unneeded check, but gcc 4.4 fails to do this.

Althouth, found originally on ARM, this bug also reproduces on x86 as well.

gcc 4.3.1 (with -m32 -O2):
test:
      pushl   %ebp
      movl    %esp, %ebp
      movl    8(%ebp), %eax
      movzbl  (%eax), %eax
      cmpb    $15, %al           // %al compared only with 15
      jne     .L8
      popl    %ebp
      jmp     func
.L8:
      popl    %ebp
      ret

gcc 4.4.0:
test:
      pushl   %ebp
      movl    %esp, %ebp
      subl    $8, %esp
      movl    8(%ebp), %eax
      movzbl  (%eax), %eax
      cmpb    $15, %al
      sete    %dl
      cmpb    $3, %al   // compiler was not able to optimize ch==3
      je      .L4
      testb   %dl, %dl
      jne     .L8
.L4:
      leave
      ret
      .p2align 4,,7
      .p2align 3
.L8:
      leave
      .p2align 4,,8
      .p2align 3
      jmp     func

Bisection shows that it was introduced by
http://gcc.gnu.org/viewcvs?view=rev&revision=140288


-- 
           Summary: [4.4 regression] missing DCE
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: alexvod at google dot com
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86-unknown-linux-gnu, arm-eabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39874

[Bug tree-optimization/39874] [4.4 regression] missing VRP (submission)

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2009-04-23 19:18 -------
Works on powerpc-darwin, where THRUTH_ORIF_EXPR is not converted into
THRUTH_OR_EXPR.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39874

[Bug tree-optimization/39874] [4.4 regression] missing VRP (submission)

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2009-04-24 09:24 -------


*** This bug has been marked as a duplicate of 28685 ***


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39874

[Bug tree-optimization/39874] [4.4 regression] missing VRP (submission)

[sandra at codesourcery dot com]

------- Comment #3 from sandra at codesourcery dot com  2010-05-24 13:08 -------
I'm testing a fix for this (better comparison combination logic in the
ifconvert pass).


-- 

sandra at codesourcery dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sandra at codesourcery dot
                   |                            |com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39874

[Bug tree-optimization/39874] [4.4 regression] missing VRP (submission)

[sandra at codesourcery dot com]

------- Comment #4 from sandra at codesourcery dot com  2010-06-01 02:22 -------
Patch posted here:

http://gcc.gnu.org/ml/gcc-patches/2010-06/msg00001.html


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39874

[Bug tree-optimization/39874] [4.4 regression] missing VRP (submission)

[sandra at gcc dot gnu dot org]

------- Comment #5 from sandra at gcc dot gnu dot org  2010-06-08 18:16 -------
Subject: Bug 39874

Author: sandra
Date: Tue Jun  8 18:15:53 2010
New Revision: 160445

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=160445
Log:
2010-06-08  Sandra Loosemore  <sandra@codesourcery.com>

        PR tree-optimization/39874
        PR middle-end/28685

        gcc/
        * gimple.h (maybe_fold_and_comparisons, maybe_fold_or_comparisons):
        Declare.
        * gimple-fold.c (canonicalize_bool, same_bool_comparison_p,
        same_bool_result_p): New.
        (and_var_with_comparison, and_var_with_comparison_1,
        and_comparisons_1, and_comparisons, maybe_fold_and_comparisons): New.
        (or_var_with_comparison, or_var_with_comparison_1,
        or_comparisons_1, or_comparisons, maybe_fold_or_comparisons): New.
        * tree-ssa-reassoc.c (eliminate_redundant_comparison): Use
        maybe_fold_and_comparisons or maybe_fold_or_comparisons instead
        of combine_comparisons.
        * tree-ssa-ifcombine.c (ifcombine_ifandif, ifcombine_iforif): Likewise.

        gcc/testsuite/
        * gcc.dg/pr39874.c: New file.

Added:
    trunk/gcc/testsuite/gcc.dg/pr39874.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/gimple-fold.c
    trunk/gcc/gimple.h
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-ifcombine.c
    trunk/gcc/tree-ssa-reassoc.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39874