[Bug tree-optimization/42614] New: FRE optimizes away valid code after IPA inlining

[Bug tree-optimization/42614] New: FRE optimizes away valid code after IPA inlining

[rahul at icerasemi dot com]

On the following test case compiled with GCC 4.4.1 release version and the
following command line

gcc -S -O2 -finline-functions-called-once -fdump-tree-all-details
-fdump-ipa-all fail.c

typedef struct SEntry
{
  unsigned char num;
} TEntry;

typedef struct STable
{
  TEntry data[2];
} TTable;


TTable *init ();
int fake_expect (int, int);
void fake_assert (int);

void
expect_func (int a, unsigned char *b) __attribute__ ((noinline));

static inline void
inlined_wrong (TEntry *entry_p, int flag);

void
inlined_wrong (TEntry *entry_p, int flag)
{
  unsigned char index;
  entry_p->num = 0;

  if (!flag)
      fake_assert (0);

  for (index = 0; index < 1; index++)
    entry_p->num++;

  asm ("before");

  if (entry_p->num)
    {
      fake_assert(0);
      asm ("#here");
    }
}

void
expect_func (int a, unsigned char *b)
{
  if (fake_expect ((a == 0), 0))
    fake_assert (0);
  if (fake_expect ((b == 0), 0))
    fake_assert (0);
}

void
broken ()
{
  unsigned char index = 0;
  TTable *table_p = init();

  inlined_wrong (&(table_p->data[1]), 1);
  expect_func (0, &index);
  inlined_wrong ((TEntry *)0xf00f, 1);

  LocalFreeMemory (&table_p);
}


we get after FRE:

broken ()
{
  unsigned char index;
  unsigned char D.1321;
  unsigned char D.1320;
  unsigned char index;
  unsigned char D.1316;
  unsigned char D.1315;
  struct TTable * table_p;
  unsigned char index;
  struct TEntry * D.1281;
  struct TTable * table_p.1;
  struct TTable * table_p.0;

<bb 2>:
  index = 0;
  table_p.0_1 = init ();
  table_p = table_p.0_1;
  table_p.1_2 = table_p.0_1;
  D.1281_3 = &table_p.1_2->data[1];
  table_p.1_2->data[1].num = 0;
  goto <bb 4>;

<bb 3>:
  D.1315_4 = D.1281_3->num;
  D.1316_5 = D.1315_4 + 1;
  D.1281_3->num = D.1316_5;
  index_7 = index_6 + 1;

<bb 4>:
  # index_6 = PHI <0(2), index_7(3)>
  if (index_6 == 0)
    goto <bb 3>;
  else
    goto <bb 5>;

<bb 5>:
  __asm__ __volatile__("before");
  D.1315_8 = 0;
  expect_func (0, &index);
  61455B->num ={v} 0;
  goto <bb 7>;

<bb 6>:
  D.1320_10 ={v} 61455B->num;
  D.1321_11 = D.1320_10 + 1;
  61455B->num ={v} D.1321_11;
  index_13 = index_12 + 1;

<bb 7>:
  # index_12 = PHI <0(5), index_13(6)>
  if (index_12 == 0)
    goto <bb 6>;
  else
    goto <bb 8>;

<bb 8>:
  __asm__ __volatile__("before");
  D.1320_14 ={v} 61455B->num;
  if (D.1320_14 != 0)
    goto <bb 9>;
  else
    goto <bb 10>;

<bb 9>:
  fake_assert (0);
  __asm__ __volatile__("#here");

<bb 10>:
  LocalFreeMemory (&table_p);
  return;

}


Note the check "if (entry_p->num)" and associated block is completely
eliminated. The dumps indicate:

Replaced table_p with table_p.0_1 in table_p.1_2 = table_p;
Replaced table_p.1_2->data[1].num with 0 in D.1315_8 =
table_p.1_2->data[1].num;
Removing basic block 6
;; basic block 6, loop depth 0, count 0
;; prev block 5, next block 7
;; pred:       5 [39.0%]  (true,exec)
;; succ:       7 [100.0%]  (fallthru,exec)
<bb 6>:
fake_assert (0);
__asm__ __volatile__("#here");


If the same code is compiled with the function "inlined_wrong" declared as

static inline void
inlined_wrong (TEntry *entry_p, int flag) __attribute__ ((always_inline));

The generated code is correct with the check in place, suggesting ipa-inline is
troublesome while early inlining works okay?


-- 
           Summary: FRE optimizes away valid code after IPA inlining
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rahul at icerasemi dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] FRE optimizes away valid code after IPA inlining

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2010-01-04 19:33 -------
Can you massage this into a runtime testcase that calls abort () when
miscompiled?


-- 

rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] FRE optimizes away valid code after IPA inlining

[stubbs at icerasemi dot com]

------- Comment #2 from stubbs at icerasemi dot com  2010-01-05 11:14 -------
This code should do it:

---
extern void *malloc(int);
extern void abort(void);
extern void free(void *);

typedef struct SEntry
{
  unsigned char num;
} TEntry;

typedef struct STable
{
  TEntry data[2];
} TTable;

TTable *init ()
{
  return malloc(sizeof(TTable));
}

void
expect_func (int a, unsigned char *b) __attribute__ ((noinline));

static inline void
inlined_wrong (TEntry *entry_p, int flag);

void
inlined_wrong (TEntry *entry_p, int flag)
{
  unsigned char index;
  entry_p->num = 0;

  if (flag == 0)
    abort();

  for (index = 0; index < 1; index++)
    entry_p->num++;

  if (!entry_p->num)
    {
      abort();
    }
}

void
expect_func (int a, unsigned char *b)
{
  if (abs ((a == 0)))
    abort ();
  if (abs ((b == 0)))
    abort ();
}

int
main ()
{
  unsigned char index = 0;
  TTable *table_p = init();
  TEntry work;

  inlined_wrong (&(table_p->data[1]), 1);
  expect_func (1, &index);
  inlined_wrong (&work, 1);

  free (table_p);

  return 1;
}
---

Built with the command line:

---
gcc -O2 -finline-functions-called-once fail.c
---

When built with GCC 4.4.1 the resultant executable incorrectly calls abort.
When built with GCC 3.4.6 the resultant executable doesn't abort.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] [4.4 Regression] FRE optimizes away valid code after IPA inlining

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2010-01-05 11:31 -------
Somehow patched openSUSE GCC 4.3 is also affected.

<bb 2>:
  # index_18 = VDEF <index_17(D)>
  index = 0;
  # index_21 = VDEF <index_18>
  # SMT.57_22 = VDEF <SMT.57_19(D)>
  # SMT.58_23 = VDEF <SMT.58_20(D)>
  table_p_1 = init ();
  D.1295_3 = &table_p_1->data[1];
  # SMT.57_24 = VDEF <SMT.57_22>
  table_p_1->data[1].num = 0;
  goto <bb 4>;

<bb 3>:
  # VUSE <SMT.58_10>
  D.1355_5 = D.1295_3->num;
  D.1356_6 = D.1355_5 + 1;
  # SMT.58_25 = VDEF <SMT.58_10>
  D.1295_3->num = D.1356_6;
  index_8 = index_7 + 1;

<bb 4>:
  # index_7 = PHI <0(2), index_8(3)>
  # SMT.58_10 = PHI <SMT.58_23(2), SMT.58_25(3)>
  if (index_7 == 0)
    goto <bb 3>;
  else
    goto <bb 5>;

<bb 5>:
  # VUSE <SMT.57_24>
  D.1355_9 = table_p_1->data[1].num;

FRE CSEs the load from table_p_1->data[1].num with the store in BB2 not
seeing the must-alias in BB3.  And it's obvious why when you look at the
vops.

SMT.58 needs to have SMT.57 in its may-aliases but doesn't have it
for some reason.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |alias, wrong-code
      Known to fail|                            |4.4.0 4.4.2
      Known to work|                            |4.2.4 4.3.4 4.5.0
   Last reconfirmed|0000-00-00 00:00:00         |2010-01-05 11:31:37
               date|                            |
            Summary|FRE optimizes away valid    |[4.4 Regression] FRE
                   |code after IPA inlining     |optimizes away valid code
                   |                            |after IPA inlining
   Target Milestone|---                         |4.4.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] FRE optimizes away valid code after IPA inlining

[rahul at icerasemi dot com]

------- Comment #3 from rahul at icerasemi dot com  2010-01-05 11:30 -------
*** Bug 42620 has been marked as a duplicate of this bug. ***


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] [4.4 Regression] FRE optimizes away valid code after IPA inlining

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2010-01-05 11:39 -------
Hm, I guess I'm the only one that is likely going to fix it.


-- 

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|2010-01-05 11:31:37         |2010-01-05 11:39:47
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] [4.4 Regression] FRE optimizes away valid code after IPA inlining

[stubbs at icerasemi dot com]

------- Comment #6 from stubbs at icerasemi dot com  2010-01-05 11:41 -------
I can try and look into it if you give me some pointers. I can guarantee I
won't be able to fix it anywhere near as quickly as you though :)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] [4.4 Regression] FRE optimizes away valid code after IPA inlining

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2010-01-05 11:57 -------
Shorter testcase, fails at -O2 -fno-early-inlining:

extern void abort(void);

typedef struct SEntry
{
  int num;
} TEntry;

typedef struct STable
{
  TEntry data[2];
} TTable;

TTable * __attribute__((noinline))
init ()
{
  static TTable t;
  return &t;
}

static inline void
inlined_wrong (TEntry *entry_p)
{
  unsigned char index;
  entry_p->num = 0;

  for (index = 0; index < 1; index++)
    entry_p->num++;

  if (!entry_p->num)
    abort();
}

void __attribute__((noinline))
expect_func (unsigned char *b)
{
  if (!b)
    abort ();
}

int
main ()
{
  unsigned char index = 0;
  TTable *table_p;

  expect_func (&index);

  table_p = init();
  inlined_wrong (&(table_p->data[1]));

  return 0;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] [4.4 Regression] FRE optimizes away valid code after IPA inlining

[rguenth at gcc dot gnu dot org]

------- Comment #8 from rguenth at gcc dot gnu dot org  2010-01-05 11:58 -------
Well, I'm sure it goes wrong in compute_flow_insensitive_aliasing - let me
have a quick look there.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] [4.4 Regression] FRE optimizes away valid code after IPA inlining

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2010-01-05 12:16 -------
Ok, it's simple.  We add false aliases to &index to both SMTs of SEntry and
STable because may_alias_p (SEntry, char) returns true as every alias-set
is a subset of alias-set zero.

But then when coming along to adding SMT aliases we do not add STable as
an alias of SEntry because they already have (false) aliases in common.
These false aliases are pruned by access_can_touch_variable later and
boom - there we go.

I have a fix.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] [4.4 Regression] FRE optimizes away valid code after IPA inlining

[rguenth at gcc dot gnu dot org]

------- Comment #10 from rguenth at gcc dot gnu dot org  2010-01-05 12:20 -------
Created an attachment (id=19472)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19472&action=view)
patch

Testing on the application that originally failed appreciated.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] [4.4 Regression] FRE optimizes away valid code after IPA inlining

[stubbs at icerasemi dot com]

------- Comment #11 from stubbs at icerasemi dot com  2010-01-05 12:23 -------
Thanks for your time and the extra quick fix! I'll do some testing with that
patch now.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] [4.4 Regression] FRE optimizes away valid code after IPA inlining

[stubbs at icerasemi dot com]

------- Comment #12 from stubbs at icerasemi dot com  2010-01-05 12:32 -------
Your patch fixes our original application. Thanks again for your help.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] [4.4 Regression] FRE optimizes away valid code after IPA inlining

[rguenth at gcc dot gnu dot org]

------- Comment #13 from rguenth at gcc dot gnu dot org  2010-01-05 13:41 -------
Subject: Bug 42614

Author: rguenth
Date: Tue Jan  5 13:41:41 2010
New Revision: 155646

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=155646
Log:
2010-01-05  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/42614
        * tree-ssa-alias.c (compute_flow_insensitive_aliasing):
        Compute SMT aliases before symbol aliases.

        * gcc.c-torture/execute/pr42614.c: New testcase.

Added:
    branches/gcc-4_4-branch/gcc/testsuite/gcc.c-torture/execute/pr42614.c
Modified:
    branches/gcc-4_4-branch/gcc/ChangeLog
    branches/gcc-4_4-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_4-branch/gcc/tree-ssa-alias.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] [4.4 Regression] FRE optimizes away valid code after IPA inlining

[rguenth at gcc dot gnu dot org]

------- Comment #15 from rguenth at gcc dot gnu dot org  2010-01-05 13:42 -------
Fixed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] [4.4 Regression] FRE optimizes away valid code after IPA inlining

[rguenth at gcc dot gnu dot org]

------- Comment #14 from rguenth at gcc dot gnu dot org  2010-01-05 13:42 -------
Subject: Bug 42614

Author: rguenth
Date: Tue Jan  5 13:42:40 2010
New Revision: 155647

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=155647
Log:
2010-01-05  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/42614
        * gcc.c-torture/execute/pr42614.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.c-torture/execute/pr42614.c
Modified:
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614

[Bug tree-optimization/42614] [4.4 Regression] FRE optimizes away valid code after IPA inlining

[rguenth at gcc dot gnu dot org]

------- Comment #16 from rguenth at gcc dot gnu dot org  2010-01-19 10:39 -------
*** Bug 42794 has been marked as a duplicate of this bug. ***


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sergei_lus at yahoo dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42614