From: Richard Biener <rguenther@suse.de>
Date: Fri, 9 May 2025 06:38:45 +0000 (+0200)
Subject: rtl-optimization/120182 - wrong-code with RTL DSE and constant addresses
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=b9434c3db900d5d037fdf2f64149b82800ceadf8;p=thirdparty%2Fgcc.git

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.
---

diff --git a/gcc/dse.cc b/gcc/dse.cc
index ffc86ffabe5..14f82c364c0 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 00000000000..5e2d171ef98
--- /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;
+}