[gcc r15-9785] rtl-optimization/120182 - wrong-code with RTL DSE and constant addresses

[Richard Biener]

https://gcc.gnu.org/g:44792a6c4253f9a5b322797ef73b9c347c223545

commit r15-9785-g44792a6c4253f9a5b322797ef73b9c347c223545
Author: Richard Biener <rguenther@suse.de>
Date:   Fri May 9 08:38:45 2025 +0200

    rtl-optimization/120182 - wrong-code with RTL DSE and constant addresses
    
    RTL DSE forms store groups from unique invariant bases but that is
    confused when presented with constant addresses where it assigns
    one store group per unique address.  That causes it to not consider
    0x101:QI to alias 0x100:SI.  Constant accesses can really alias
    to every object, in practice they appear for I/O and for access
    to objects fixed via linker scripts for example.  So simply avoid
    registering a store group for them.
    
            PR rtl-optimization/120182
            * dse.cc (canon_address): Constant addresses have no
            separate store group.
    
            * gcc.dg/torture/pr120182.c: New testcase.
    
    (cherry picked from commit b9434c3db900d5d037fdf2f64149b82800ceadf8)

Diff:
---
 gcc/dse.cc                              |  5 +++-
 gcc/testsuite/gcc.dg/torture/pr120182.c | 42 +++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/gcc/dse.cc b/gcc/dse.cc
index ffc86ffabe5e..14f82c364c06 100644
--- a/gcc/dse.cc
+++ b/gcc/dse.cc
@@ -1190,7 +1190,10 @@ canon_address (rtx mem,
       address = strip_offset_and_add (address, offset);
 
       if (ADDR_SPACE_GENERIC_P (MEM_ADDR_SPACE (mem))
-	  && const_or_frame_p (address))
+	  && const_or_frame_p (address)
+	  /* Literal addresses can alias any base, avoid creating a
+	     group for them.  */
+	  && ! CONST_SCALAR_INT_P (address))
 	{
 	  group_info *group = get_group_info (address);
 
diff --git a/gcc/testsuite/gcc.dg/torture/pr120182.c b/gcc/testsuite/gcc.dg/torture/pr120182.c
new file mode 100644
index 000000000000..5e2d171ef985
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr120182.c
@@ -0,0 +1,42 @@
+/* { dg-do run { target { { *-*-linux* *-*-gnu* *-*-uclinux* } && mmap } } } */
+
+#include <unistd.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+
+struct S
+{
+  struct S *next;
+};
+
+static void __attribute__((noipa))
+allocate(void *addr, unsigned long long size)
+{
+  void *ptr = mmap((void *)addr, size,
+		   PROT_READ | PROT_WRITE,
+		   MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED_NOREPLACE,
+		   -1, 0);
+  if(ptr != addr)
+    exit(0);
+}
+
+int main (void)
+{
+  int size = 0x8000;
+  char *ptr = (char *)0x288000ull;
+  allocate((void *)ptr, size);
+
+  struct S *s1 = (struct S *)ptr;
+  struct S *s2 = (struct S *)256;
+  for (int i = 0; i < 3; i++)
+    {
+      for(char *addr = (char *)s1; addr < (char *)s1 + sizeof(*s1); ++addr)
+	*addr = 0;
+
+      if(s1->next)
+	s1->next = s1->next->next = s2;
+      else
+	s1->next = s2;
+    }
+  return 0;
+}