[Bug tree-optimization/113419] New: SRA should replace some aggregate copies by load/store

[Bug tree-optimization/113419] New: SRA should replace some aggregate copies by load/store

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113419

            Bug ID: 113419
           Summary: SRA should replace some aggregate copies by load/store
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

For example gcc.dg/tree-ssa/pr94969.c has

int a = 0, b = 0, c = 0;
struct S {
  signed m : 7;
  signed e : 2;
};
struct S f[2] = {{0, 0}, {0, 0}};
struct S g = {0, 0};

void __attribute__((noinline))
k()
{
  for (; c <= 1; c++) {
    f[b] = g;
    f[b].e ^= 1;
  }
}

the aggregate copy f[b] = g isn't touched by SRA because it's global
variables.  For locals we'd end up with sth like

  <unnamed-signed:2> g$e;
  <unnamed-signed:7> g$m;
  struct S g;
  struct S a[2];

  <bb 2> :
  g$m_7 = 0;
  g$e_8 = 0;
  MEM[(struct S *)&a + 4B].m = g$m_7;
  MEM[(struct S *)&a + 4B].e = g$e_8;

so bit-precision integers.  That might be good, esp. if there's field
uses around.

When the global variable variant is expaneded on RTL we see a simple
SImode load and a SImode store.  That means we should ideally treat
aggregate copies like memcpy (&dest, &src, sizeof (dest)) and then
fold it that way.

But we should let SRA have a chance at decomposing first so this
shouldn't be done as part of general folding but instead by late SRA
for aggregate copies it didn't touch.  For the gcc.dg/tree-ssa/pr94969.c
testcase this then allows GIMPLE invariant motion to hoist the load
from g, otherwise we rely on RTL PRE for this which is prone to PR113395.

[Bug tree-optimization/113419] SRA should replace some aggregate copies by load/store

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113419

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2024-01-16
             Status|UNCONFIRMED                 |ASSIGNED

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I'll take this for next stage1, factoring out sth from
gimple_fold_builtin_memory_op

[Bug tree-optimization/113419] SRA should replace some aggregate copies by load/store

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113419

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
           Severity|normal                      |enhancement

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I suspect there might be a few duplicates floating around too.

[Bug tree-optimization/113419] SRA should replace some aggregate copies by load/store

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113419

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=99728

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
PR 99728 for one, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99728#c17 .