[gcc r16-9386] out-of-SSA: Preserve storage for split partition decls [PR126341]

https://gcc.gnu.org/g:06f9f3e43ce19f5882e180a3e5c1373a016d29e4

commit r16-9386-g06f9f3e43ce19f5882e180a3e5c1373a016d29e4
Author: Kyrylo Tkachov <[email protected]>
Date:   Tue Jul 21 02:44:06 2026 -0700

    out-of-SSA: Preserve storage for split partition decls [PR126341]
    
    create_tmp_var_raw marks a replacement declaration as ignored.  At -O0,
    this can change use_register_for_decl from memory for the original user
    declaration to a pseudo for the replacement.  A partition can already own
    memory from a parameter default definition, which then makes set_rtl reject
    that memory for another name in the partition.
    
    If the replacement would use a register, copy DECL_IGNORED_P so it keeps the
    storage choice made during coalescing.  Keep declarations that already use
    memory unchanged.  Add a checking assertion for the memory invariant.
    
    Bootstrapped and tested on aarch64-none-linux-gnu and x86_64-linux.
    
    gcc/ChangeLog:
    
            PR middle-end/126341
            * tree-outof-ssa.cc (split_overlapping_partition_decls): Preserve
            DECL_IGNORED_P.  Check that the replacement uses memory.
    
    gcc/testsuite/ChangeLog:
    
            PR middle-end/126341
            * gcc.dg/pr126341.c: New test.
    
    Signed-off-by: Kyrylo Tkachov <[email protected]>
    (cherry picked from commit 7459f9136500bfb881902834d56fb110b77909f2)

Diff:
---
 gcc/testsuite/gcc.dg/pr126341.c | 53 +++++++++++++++++++++++++++++++++++++++++
 gcc/tree-outof-ssa.cc           |  5 ++++
 2 files changed, 58 insertions(+)

diff --git a/gcc/testsuite/gcc.dg/pr126341.c b/gcc/testsuite/gcc.dg/pr126341.c
new file mode 100644
index 000000000000..76ed1d889e48
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr126341.c
@@ -0,0 +1,53 @@
+/* { dg-do compile { target bitint575 } } */
+/* { dg-options "-fnon-call-exceptions -ftree-coalesce-vars" } */
+/* { dg-prune-output "division by zero" } */
+
+/* PR middle-end/126341 */
+
+#define N 0x200000000uwb
+#define DIV0 (1 / 0)
+
+struct {
+  char j[8];
+} k;
+char l;
+int m, p, q, r;
+long n;
+_Complex o;
+int s;
+_BitInt (256) aa;
+
+void
+foo (_BitInt (8) t)
+{
+  int ah, ai, aj = 1, ak, al = 1, am = 1, an = 1, ao = 1, ap = 1, aq = DIV0;
+  int ar = 1, as = 1, at, au = DIV0;
+  int av = 1;
+  _BitInt (7) c = ak--;
+  char aw = 1, ax = 1, ay = 1, az = 1, a = 1, d = 1, e = 1;
+  int bfbg = 1, bh = 1, bi = p += ai -= __sync_add_and_fetch (&s, 1);
+  int bj;
+  int bk, blbm = 1, bt = 1, bu = 1, bv = __atomic_or_fetch (&aa, 1, 1);
+  int bn = 1, bobp = 1, br = 1, bs = 1;
+  unsigned b, cc;
+  char cf, ce;
+
+  if (bj)
+    goto ca;
+  b = 1, cc = 1;
+  for (;;);
+  ce = q;
+  cf = o ? 1
+    :
+    __builtin_stdc_rotate_left (__builtin_stdc_rotate_left
+				(c - 0x3bfuwb, br), n & 1) ? 3 : 3;
+  1 +
+    az & 1 | N << -az & m | ((az & 1 | N) << -az & 1 ? 0 : 7u) & 1 |
+    ((az & 1 | N) - az & m | az & 1 | N) < 7 > -c & 1;
+ca:
+  s %= __builtin_stdc_rotate_left (cc, ah);
+  at /= r ^= ({ __auto_type cg = 0; __auto_type ch = 0; 0; });
+
+  long ci = bk % cf;
+  _BitInt (8) cj = l ? t : k.j[3];
+}
diff --git a/gcc/tree-outof-ssa.cc b/gcc/tree-outof-ssa.cc
index 918dbbedde36..17d5e70e71d8 100644
--- a/gcc/tree-outof-ssa.cc
+++ b/gcc/tree-outof-ssa.cc
@@ -1101,6 +1101,11 @@ split_overlapping_partition_decls (var_map map)
 	continue;
 
       tree nvar = create_tmp_var_raw (TREE_TYPE (var));
+      /* Avoid a register-only NVAR when the partition already has a MEM,
+	 since set_rtl cannot assign that MEM to NVAR.  */
+      if (use_register_for_decl (nvar))
+	DECL_IGNORED_P (nvar) = DECL_IGNORED_P (var);
+      gcc_checking_assert (!use_register_for_decl (nvar));
       DECL_CONTEXT (nvar) = DECL_CONTEXT (var);
       DECL_SOURCE_LOCATION (nvar) = DECL_SOURCE_LOCATION (var);
       SET_DECL_ALIGN (nvar, DECL_ALIGN (var));