[Bug tree-optimization/24689] New: store_ccp is missing an opportunity!?

[Bug tree-optimization/24689] New: store_ccp is missing an opportunity!?

[kazu at gcc dot gnu dot org]

Consider:

extern void bar (unsigned int);

int
foo (void)
{
  char buf[1] = { 3 };
  const char *p = buf;
  const char **q = &p;
  unsigned int ch;
  switch (**q)
    {
    case 1:  ch = 5; break;
    default: ch = 0; break;
    }

#if 1
  bar (ch);
#endif
  return ch;
}

This function should be optimized to "return 0;", but it isn't.

Interestingly, if you change "#if 1" to "#if 0", you are going to get
this optimized.

The testcase is derived from PR 20583.


-- 
           Summary: store_ccp is missing an opportunity!?
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24689

[Bug tree-optimization/24689] store_ccp is missing an opportunity because of call clobber/alias load?

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2005-11-06 04:34 -------
Looks like another one of the call clobbered bugs:
Variable: buf, UID 1612, char[1], is an alias tag, is addressable, call
clobbered, default def: buf_2

Though that should not matter.
Here is a testcase where call clobberness is correct but it should not matter
as there is no way for the change to happen:
extern void bar (unsigned int);
extern void bar1 (const char **);

int
foo (void)
{
  char buf[1] = { 3 };
  const char *p = buf;
  const char **q = &p;
  unsigned int ch;
  switch (**q)
    {
    case 1:  ch = 5; break;
    default: ch = 0; break;
    }

  bar (ch);
  bar1 (q);
  return ch;
}


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |alias
   Last reconfirmed|0000-00-00 00:00:00         |2005-11-06 04:34:23
               date|                            |
            Summary|store_ccp is missing an     |store_ccp is missing an
                   |opportunity!?               |opportunity because of call
                   |                            |clobber/alias load?


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24689

[Bug tree-optimization/24689] store_ccp is missing an opportunity because of call clobber/alias load?

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2005-11-06 04:47 -------
Note switch statements here have nothing to do with the real issue:
extern void bar (unsigned int);
extern void bar1 (const char **);

int
foo (void)
{
  char buf[1] = { 3 };
  const char *p = buf;
  const char **q = &p;
  unsigned int ch;
  if(**q)
    {
            ch = 1;
    }
  else ch =2;

  bar (ch);
  bar1 (q);
  return ch;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24689

[Bug tree-optimization/24689] store_ccp does nothing for array references

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2005-11-06 04:50 -------
(In reply to comment #0)
> This function should be optimized to "return 0;", but it isn't.
> Interestingly, if you change "#if 1" to "#if 0", you are going to get
> this optimized.
Not really because SRA works then, using -fno-tree-sra will show the same
issue.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|store_ccp is missing an     |store_ccp does nothing for
                   |opportunity because of call |array references
                   |clobber/alias load?         |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24689

[Bug tree-optimization/24689] store_ccp does nothing for array references

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2005-11-06 04:52 -------
Here is another testcase:
extern void bar (unsigned int);
extern void bar1 (const char **);

char buf[1];
int
foo (void)
{
  const char *p = buf;
  const char **q = &p;
  buf[0] = 3;
  unsigned int ch;
  if(**q)
    {
            ch = 1;
    }
  else ch =2;

  return ch;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24689

[Bug tree-optimization/24689] store_ccp does nothing for array references

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2006-01-15 21:35 -------
I am going to look into this soon but I don't think it is an aliasing issue as
shown by:
  #   SFT.0_6 = V_MUST_DEF <SFT.0_5>;
  buf[0] = 3;
  #   VUSE <SFT.0_6>;
  D.1523_8 = buf[0];


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24689

[Bug tree-optimization/24689] operand_equal_p does not return true for some equivalent ARRAY_REF

[pinskia at gcc dot gnu dot org]

------- Comment #6 from pinskia at gcc dot gnu dot org  2006-01-16 06:02 -------
The problem here is that operand_equal_p returns false for these two trees:
<array_ref 0x41da4b94
    type <integer_type 0x41d1b180 char sizes-gimplified public QI
        size <integer_cst 0x41d0a320 constant invariant 8>
        unit size <integer_cst 0x41d0a340 constant invariant 1>
        align 8 symtab 0 alias set -1 precision 8 min <integer_cst 0x41d0a3a0
-128> max <integer_cst 0x41d0a420 127>
        pointer_to_this <pointer_type 0x41d23120>>

    arg 0 <var_decl 0x41da2540 buf
        type <array_type 0x41da24e0 type <integer_type 0x41d1b180 char>
            QI size <integer_cst 0x41d0a320 8> unit size <integer_cst
0x41d0a340 1>
            align 8 symtab 0 alias set -1 domain <integer_type 0x41da2480>>
        addressable used public static common QI file t.c line 4 size
<integer_cst 0x41d0a320 8> unit size <integer_cst 0x41d0a340 1>
        align 8
        chain <function_decl 0x41da3680 foo type <function_type 0x41d236c0>
            public static SI file t.c line 7 initial <block 0x41da4bfc> result
<result_decl 0x41d12268 D.1518>
            (mem:SI (symbol_ref:SI ("foo") [flags 0x103] <function_decl
0x41da3680 foo>) [0 S4 A8])
            saved-insns 0x41d85c00>>
    arg 1 <integer_cst 0x41d0ab40 type <integer_type 0x41d1b2a0 int> constant
invariant 0>>

and
 <array_ref 0x41dab6b4
    type <integer_type 0x41d23300 char readonly sizes-gimplified public QI
        size <integer_cst 0x41d0a320 constant invariant 8>
        unit size <integer_cst 0x41d0a340 constant invariant 1>
        align 8 symtab 0 alias set -1 precision 8 min <integer_cst 0x41d0a3a0
-128> max <integer_cst 0x41d0a420 127>
        pointer_to_this <pointer_type 0x41d23360>>

    arg 0 <var_decl 0x41da2540 buf
        type <array_type 0x41da24e0 type <integer_type 0x41d1b180 char>
            QI size <integer_cst 0x41d0a320 8> unit size <integer_cst
0x41d0a340 1>
            align 8 symtab 0 alias set -1 domain <integer_type 0x41da2480>>
        addressable used public static common QI file t.c line 4 size
<integer_cst 0x41d0a320 8> unit size <integer_cst 0x41d0a340 1>
        align 8
        chain <function_decl 0x41da3680 foo type <function_type 0x41d236c0>
            public static SI file t.c line 7 initial <block 0x41da4bfc> result
<result_decl 0x41d12268 D.1518>
            (mem:SI (symbol_ref:SI ("foo") [flags 0x103] <function_decl
0x41da3680 foo>) [0 S4 A8])
            saved-insns 0x41d85c00>>
    arg 1 <integer_cst 0x41d76600 type <integer_type 0x41da2480> constant
invariant 0>
    arg 2 <integer_cst 0x41d0a2a0 type <integer_type 0x41d1b000 long unsigned
int> constant invariant 0> arg 3 <integer_cst 0x41d0a340 1>>

Even they point to the same spot, it does not work as the two array reference
have different arg2/arg3.

So Store_CCP is doing the correct thing, just the function it depends on is
not.

And the reason for this problem is because when changing **q into buf[0], it
does not fill out those two arguments to the tree.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|alias                       |
            Summary|store_ccp does nothing for  |operand_equal_p does not
                   |array references            |return true for some
                   |                            |equivalent ARRAY_REF


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24689

[Bug tree-optimization/24689] operand_equal_p does not return true for some equivalent ARRAY_REF

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2007-04-11 11:13 -------
I have a patch.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2006-10-30 02:29:43         |2007-04-11 11:13:33
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24689

[Bug tree-optimization/24689] operand_equal_p does not return true for some equivalent ARRAY_REF

[pinskia at gcc dot gnu dot org]

------- Comment #8 from pinskia at gcc dot gnu dot org  2007-04-11 13:03 -------
I should make a note here that if operand_equal_p returns true, iterative hash
has to be the same also.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24689

[Bug tree-optimization/24689] operand_equal_p does not return true for some equivalent ARRAY_REF

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2007-04-11 14:51 -------
Luckily iterative hash hashes low/high of integer consts only, not the type.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24689

[Bug tree-optimization/24689] operand_equal_p does not return true for some equivalent ARRAY_REF

[rguenth at gcc dot gnu dot org]

------- Comment #10 from rguenth at gcc dot gnu dot org  2007-04-12 10:16 -------
Subject: Bug 24689

Author: rguenth
Date: Thu Apr 12 10:15:53 2007
New Revision: 123736

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=123736
Log:
2007-04-12  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/24689
        PR tree-optimization/31307
        * fold-const.c (operand_equal_p): Compare INTEGER_CST array
        indices by value.
        * gimplify.c (canonicalize_addr_expr): To be consistent with
        gimplify_compound_lval only set operands two and three of
        ARRAY_REFs if they are not gimple_min_invariant.  This makes
        it never at this place.
        * tree-ssa-ccp.c (maybe_fold_offset_to_array_ref): Likewise.

        * g++.dg/tree-ssa/pr31307.C: New testcase.
        * gcc.dg/tree-ssa/pr24689.c: Likewise.

Added:
    trunk/gcc/testsuite/g++.dg/tree-ssa/pr31307.C
    trunk/gcc/testsuite/gcc.dg/tree-ssa/pr24689.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/fold-const.c
    trunk/gcc/gimplify.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-ccp.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24689

[Bug tree-optimization/24689] operand_equal_p does not return true for some equivalent ARRAY_REF

[rguenth at gcc dot gnu dot org]

------- Comment #11 from rguenth at gcc dot gnu dot org  2007-04-12 10:28 -------
Fixed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24689