[Bug c/100260] New: DSE: join stores

[Bug c/100260] New: DSE: join stores

[david.bolvansky at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100260

            Bug ID: 100260
           Summary: DSE: join stores
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: david.bolvansky at gmail dot com
  Target Milestone: ---

#include <string.h>

struct pam {
  void *p1;
  void *p2;
  #ifdef LONG
  unsigned long size;
  #else
  unsigned int pad;
  unsigned int size;
  #endif
};

extern int use(struct pam *param);

unsigned int foo(void) {
  struct pam s_pam;
  memset(&s_pam, 0, sizeof(struct pam));
  s_pam.size = 1;
  return use(&s_pam);
}

INT

foo():
  sub rsp, 40
  pxor xmm0, xmm0
  mov rdi, rsp
  mov DWORD PTR [rsp+16], 0
  mov DWORD PTR [rsp+20], 1
  movaps XMMWORD PTR [rsp], xmm0
  call use(pam*)
  add rsp, 40
  ret

LONG

foo():
  sub rsp, 40
  pxor xmm0, xmm0
  mov rdi, rsp
  movaps XMMWORD PTR [rsp], xmm0
  mov QWORD PTR [rsp+16], 1
  call use(pam*)
  add rsp, 40
  ret

Stores
  mov DWORD PTR [rsp+16], 0
  mov DWORD PTR [rsp+20], 1
can be replaced with one mov QWORD..

[Bug tree-optimization/100260] DSE: join stores

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100260

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
                 CC|                            |ebotcazou at gcc dot gnu.org,
                   |                            |jakub at gcc dot gnu.org
   Last reconfirmed|                            |2021-04-26

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  store-merging doesn't seem to consider memset() as candidate to
merge with:

Processing basic block <2>:
Starting active chain number 1 with statement:
s_pam.size = 1;
The base object is:
&s_pam
stmt causes chain termination:
_1 = use (&s_pam);
Terminating chain with 1 stores

unsigned int foo ()
{
  struct pam s_pam;
  int _1;
  unsigned int _6;

  <bb 2> [local count: 1073741824]:
  memset (&s_pam, 0, 20);
  s_pam.size = 1;
  _1 = use (&s_pam);
  _6 = (unsigned int) _1;
  s_pam ={v} {CLOBBER};
  return _6;

}