[Bug tree-optimization/106786] [12/13 Regression] SRA regression causes extra instructions sometimes

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106786

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
             Blocks|                            |100453
                 CC|                            |jamborm at gcc dot gnu.org

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
The difference is (before SRA) good vs. bad:

+Rejected (2400): not aggregate: x
+Rejected (2401): not aggregate: y
+Candidate (2452): D.2452
+Rejected (2451): not aggregate: d
+Candidate (2447): D.2447
+Rejected (2446): not aggregate: d
+Rejected (2445): not aggregate: carry
+Candidate (2430): a
+Candidate (2404): z
+! Disqualifying z - Encountered a store to a read-only decl.
+Will attempt to totally scalarize D.2447 (UID: 2447): 
+Will attempt to totally scalarize D.2452 (UID: 2452): 
 Changing the type of a replacement for a offset: 64, size: 8  to an integer.
-Created a replacement for a offset: 64, size: 8: a$8D.2422
+Created a replacement for a offset: 64, size: 8: a$8D.2453

so it looks like SRA is confused by 'z' being declared const?

Thus likely caused by r12-1529-gd7deee423f993b

diff --git a/gcc/tree-sra.cc b/gcc/tree-sra.cc
index 1a3e12f18cc..1f4e5987292 100644
--- a/gcc/tree-sra.cc
+++ b/gcc/tree-sra.cc
@@ -922,12 +922,6 @@ create_access (tree expr, gimple *stmt, bool write)
   if (!DECL_P (base) || !bitmap_bit_p (candidate_bitmap, DECL_UID (base)))
     return NULL;

-  if (write && TREE_READONLY (base))
-    {
-      disqualify_candidate (base, "Encountered a store to a read-only decl.");
-      return NULL;
-    }
-
   HOST_WIDE_INT offset, size, max_size;
   if (!poffset.is_constant (&offset)
       || !psize.is_constant (&size)

fixes the regression (leaving the rest of the checks in place, but not sure
how safe that is).

Martin?


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100453
[Bug 100453] [12 Regression] wrong code at -O1 and above since r12-434