[Bug tree-optimization/93271] [9/10/11/12 regression] SRA producing wrong code on denormals

[Bug tree-optimization/93271] [9/10/11/12 regression] SRA producing wrong code on denormals

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93271

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|8.5                         |9.4

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 8 branch is being closed.

[Bug tree-optimization/93271] [9/10/11/12 regression] SRA producing wrong code on denormals

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93271

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.4                         |9.5

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9.4 is being released, retargeting bugs to GCC 9.5.

[Bug tree-optimization/93271] [10/11/12/13 regression] SRA producing wrong code on denormals

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93271

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.5                         |10.4

--- Comment #11 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9 branch is being closed

[Bug tree-optimization/93271] [10/11/12/13 regression] SRA producing wrong code on denormals

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93271

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.4                        |10.5

--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 10.4 is being released, retargeting bugs to GCC 10.5.

[Bug tree-optimization/93271] [10/11/12/13 regression] SRA producing wrong code on denormals

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93271

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |i?86-*-*
   Last reconfirmed|2022-01-29 00:00:00         |2023-4-13

--- Comment #13 from Richard Biener <rguenth at gcc dot gnu.org> ---
The issue is that on some targets (like i386) a FP load/store isn't a noop
but alters the bit representation.  SRA in this case sees aggregate
store/load and scalar float store/load (but this one conditional).

In case there's a non-FP load or store of the part of the aggregate that's
also accessed as float there's no way to correctly perform the scalar
ops _but at the very point they are done originally_.

So the issue is we're doing the replacement in a non-flow-sensitive manner.
Of course when done flow-sentitive then the replacement will be pointless.
For long/double it's the same.  There is currently no predicate that will
tell whether a target implements no-op reg = FP-mem; FP-mem = reg; so the
only "safe" fix would be to avoid scalarization of FP parts when the
initialization isn't provably done with FP stores.

 int main ()
 {
+  float a$b;
   union test a;
   float _1;
   float _2;
@@ -82,14 +70,16 @@

   <bb 2> :
   a = set (); [return slot optimization]
+  a$b_7 = a.b;
   goto <bb 4>; [INV]

   <bb 3> :
-  _1 = a.b;
+  _1 = a$b_8;
   _2 = _1 + 1.0e+0;
-  a.b = _2;
+  a$b_11 = _2;

   <bb 4> :
+  # a$b_8 = PHI <a$b_7(2), a$b_11(3)>
   val.0_3 ={v} val;
   if (val.0_3 != 0)
     goto <bb 3>; [INV]
@@ -97,8 +87,8 @@
     goto <bb 5>; [INV]

   <bb 5> :
+  a.b = a$b_8;
   get (a);
-  a ={v} {CLOBBER(eol)};
   return 0;

[Bug tree-optimization/93271] [11/12/13/14 regression] SRA producing wrong code on denormals

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93271

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.5                        |11.5

--- Comment #14 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10 branch is being closed.

[Bug tree-optimization/93271] [11/12/13/14 regression] SRA producing wrong code on denormals

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93271

--- Comment #15 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
It is even worse with `int128_t` and `long double` due to `long double` having
padding bits (and a padding byte). So it is not only denormals but even bits in
the padding bits/byte that might get lost.

[Bug tree-optimization/93271] [11/12/13/14 regression] SRA producing wrong code on denormals

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93271

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrew at ziglang dot org

--- Comment #16 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 112521 has been marked as a duplicate of this bug. ***

[Bug tree-optimization/93271] [11/12/13/14 regression] SRA producing wrong code on denormals

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93271

--- Comment #17 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Ping?