[GCC13,V4,2/2] Use array_at_struct_end_p in __builtin_object_size [PR101836]

diff --git a/gcc/testsuite/gcc.dg/pr101836.c b/gcc/testsuite/gcc.dg/pr101836.c
new file mode 100644
index 000000000000..efad02cfe899
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr101836.c
@@ -0,0 +1,60 @@ 
+/* -fstrict-flex-arrays is aliased with -ftrict-flex-arrays=3, which is the
+   strictest, only [] is treated as flexible array.  */ 
+/* PR tree-optimization/101836 */
+/* { dg-do run } */
+/* { dg-options "-O2 -fstrict-flex-arrays" } */
+
+#include <stdio.h>
+
+#define expect(p, _v) do { \
+    size_t v = _v; \
+    if (p == v) \
+        printf("ok:  %s == %zd\n", #p, p); \
+    else \
+	{  \
+          printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
+	  __builtin_abort (); \
+	} \
+} while (0);
+
+struct trailing_array_1 {
+    int a;
+    int b;
+    int c[4];
+};
+
+struct trailing_array_2 {
+    int a;
+    int b;
+    int c[1];
+};
+
+struct trailing_array_3 {
+    int a;
+    int b;
+    int c[0];
+};
+struct trailing_array_4 {
+    int a;
+    int b;
+    int c[];
+};
+
+void __attribute__((__noinline__)) stuff(
+    struct trailing_array_1 *normal,
+    struct trailing_array_2 *trailing_1,
+    struct trailing_array_3 *trailing_0,
+    struct trailing_array_4 *trailing_flex)
+{
+    expect(__builtin_object_size(normal->c, 1), 16);
+    expect(__builtin_object_size(trailing_1->c, 1), 4);
+    expect(__builtin_object_size(trailing_0->c, 1), 0);
+    expect(__builtin_object_size(trailing_flex->c, 1), -1);
+}
+
+int main(int argc, char *argv[])
+{
+    stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void *)argv[0]);
+
+    return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/pr101836_1.c b/gcc/testsuite/gcc.dg/pr101836_1.c
new file mode 100644
index 000000000000..e2931ce1012e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr101836_1.c
@@ -0,0 +1,60 @@ 
+/* -fstrict-flex-arrays=3 is the strictest, only [] is treated as
+   flexible array.  */ 
+/* PR tree-optimization/101836 */
+/* { dg-do run } */
+/* { dg-options "-O2 -fstrict-flex-arrays=3" } */
+
+#include <stdio.h>
+
+#define expect(p, _v) do { \
+    size_t v = _v; \
+    if (p == v) \
+        printf("ok:  %s == %zd\n", #p, p); \
+    else \
+	{  \
+          printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
+	  __builtin_abort (); \
+	} \
+} while (0);
+
+struct trailing_array_1 {
+    int a;
+    int b;
+    int c[4];
+};
+
+struct trailing_array_2 {
+    int a;
+    int b;
+    int c[1];
+};
+
+struct trailing_array_3 {
+    int a;
+    int b;
+    int c[0];
+};
+struct trailing_array_4 {
+    int a;
+    int b;
+    int c[];
+};
+
+void __attribute__((__noinline__)) stuff(
+    struct trailing_array_1 *normal,
+    struct trailing_array_2 *trailing_1,
+    struct trailing_array_3 *trailing_0,
+    struct trailing_array_4 *trailing_flex)
+{
+    expect(__builtin_object_size(normal->c, 1), 16);
+    expect(__builtin_object_size(trailing_1->c, 1), 4);
+    expect(__builtin_object_size(trailing_0->c, 1), 0);
+    expect(__builtin_object_size(trailing_flex->c, 1), -1);
+}
+
+int main(int argc, char *argv[])
+{
+    stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void *)argv[0]);
+
+    return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/pr101836_2.c b/gcc/testsuite/gcc.dg/pr101836_2.c
new file mode 100644
index 000000000000..78974187721f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr101836_2.c
@@ -0,0 +1,60 @@ 
+/* When -fstrict-flex-arrays=2, only [] and [0] are treated as flexiable
+   arrays.  */
+/* PR tree-optimization/101836 */
+/* { dg-do run } */
+/* { dg-options "-O2 -fstrict-flex-arrays=2" } */
+
+#include <stdio.h>
+
+#define expect(p, _v) do { \
+    size_t v = _v; \
+    if (p == v) \
+        printf("ok:  %s == %zd\n", #p, p); \
+    else \
+	{  \
+          printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
+	  __builtin_abort (); \
+	} \
+} while (0);
+
+struct trailing_array_1 {
+    int a;
+    int b;
+    int c[4];
+};
+
+struct trailing_array_2 {
+    int a;
+    int b;
+    int c[1];
+};
+
+struct trailing_array_3 {
+    int a;
+    int b;
+    int c[0];
+};
+struct trailing_array_4 {
+    int a;
+    int b;
+    int c[];
+};
+
+void __attribute__((__noinline__)) stuff(
+    struct trailing_array_1 *normal,
+    struct trailing_array_2 *trailing_1,
+    struct trailing_array_3 *trailing_0,
+    struct trailing_array_4 *trailing_flex)
+{
+    expect(__builtin_object_size(normal->c, 1), 16);
+    expect(__builtin_object_size(trailing_1->c, 1), 4);
+    expect(__builtin_object_size(trailing_0->c, 1), -1);
+    expect(__builtin_object_size(trailing_flex->c, 1), -1);
+}
+
+int main(int argc, char *argv[])
+{
+    stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void *)argv[0]);
+
+    return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/pr101836_3.c b/gcc/testsuite/gcc.dg/pr101836_3.c
new file mode 100644
index 000000000000..0e69388e81fb
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr101836_3.c
@@ -0,0 +1,60 @@ 
+/* When -fstrict-flex-arrays=1, [], [0], and [1] are treated as flexible
+   arrays.  */
+/* PR tree-optimization/101836 */
+/* { dg-do run } */
+/* { dg-options "-O2 -fstrict-flex-arrays=1" } */
+
+#include <stdio.h>
+
+#define expect(p, _v) do { \
+    size_t v = _v; \
+    if (p == v) \
+        printf("ok:  %s == %zd\n", #p, p); \
+    else \
+	{  \
+          printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
+	  __builtin_abort (); \
+	} \
+} while (0);
+
+struct trailing_array_1 {
+    int a;
+    int b;
+    int c[4];
+};
+
+struct trailing_array_2 {
+    int a;
+    int b;
+    int c[1];
+};
+
+struct trailing_array_3 {
+    int a;
+    int b;
+    int c[0];
+};
+struct trailing_array_4 {
+    int a;
+    int b;
+    int c[];
+};
+
+void __attribute__((__noinline__)) stuff(
+    struct trailing_array_1 *normal,
+    struct trailing_array_2 *trailing_1,
+    struct trailing_array_3 *trailing_0,
+    struct trailing_array_4 *trailing_flex)
+{
+    expect(__builtin_object_size(normal->c, 1), 16);
+    expect(__builtin_object_size(trailing_1->c, 1), -1);
+    expect(__builtin_object_size(trailing_0->c, 1), -1);
+    expect(__builtin_object_size(trailing_flex->c, 1), -1);
+}
+
+int main(int argc, char *argv[])
+{
+    stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void *)argv[0]);
+
+    return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/pr101836_4.c b/gcc/testsuite/gcc.dg/pr101836_4.c
new file mode 100644
index 000000000000..e0025aa9a7b5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr101836_4.c
@@ -0,0 +1,60 @@ 
+/* when -fstrict-flex-arrays=0, all trailing arrays are treated as
+   flexible arrays.  */
+/* PR tree-optimization/101836 */
+/* { dg-do run } */
+/* { dg-options "-O2 -fstrict-flex-arrays=0" } */
+
+#include <stdio.h>
+
+#define expect(p, _v) do { \
+    size_t v = _v; \
+    if (p == v) \
+        printf("ok:  %s == %zd\n", #p, p); \
+    else \
+	{  \
+          printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
+	  __builtin_abort (); \
+	} \
+} while (0);
+
+struct trailing_array_1 {
+    int a;
+    int b;
+    int c[4];
+};
+
+struct trailing_array_2 {
+    int a;
+    int b;
+    int c[1];
+};
+
+struct trailing_array_3 {
+    int a;
+    int b;
+    int c[0];
+};
+struct trailing_array_4 {
+    int a;
+    int b;
+    int c[];
+};
+
+void __attribute__((__noinline__)) stuff(
+    struct trailing_array_1 *normal,
+    struct trailing_array_2 *trailing_1,
+    struct trailing_array_3 *trailing_0,
+    struct trailing_array_4 *trailing_flex)
+{
+    expect(__builtin_object_size(normal->c, 1), -1);
+    expect(__builtin_object_size(trailing_1->c, 1), -1);
+    expect(__builtin_object_size(trailing_0->c, 1), -1);
+    expect(__builtin_object_size(trailing_flex->c, 1), -1);
+}
+
+int main(int argc, char *argv[])
+{
+    stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void *)argv[0]);
+
+    return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/pr101836_5.c b/gcc/testsuite/gcc.dg/pr101836_5.c
new file mode 100644
index 000000000000..0ad8bbf693ce
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr101836_5.c
@@ -0,0 +1,60 @@ 
+/* -fno-strict-flex-arrays is aliased to -fstrict-flex-arrays=0,
+   all trailing arrays are treated as flexible array.  */
+/* PR tree-optimization/101836 */
+/* { dg-do run } */
+/* { dg-options "-O2 -fno-strict-flex-arrays" } */
+
+#include <stdio.h>
+
+#define expect(p, _v) do { \
+    size_t v = _v; \
+    if (p == v) \
+        printf("ok:  %s == %zd\n", #p, p); \
+    else \
+	{  \
+          printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
+	  __builtin_abort (); \
+	} \
+} while (0);
+
+struct trailing_array_1 {
+    int a;
+    int b;
+    int c[4];
+};
+
+struct trailing_array_2 {
+    int a;
+    int b;
+    int c[1];
+};
+
+struct trailing_array_3 {
+    int a;
+    int b;
+    int c[0];
+};
+struct trailing_array_4 {
+    int a;
+    int b;
+    int c[];
+};
+
+void __attribute__((__noinline__)) stuff(
+    struct trailing_array_1 *normal,
+    struct trailing_array_2 *trailing_1,
+    struct trailing_array_3 *trailing_0,
+    struct trailing_array_4 *trailing_flex)
+{
+    expect(__builtin_object_size(normal->c, 1), -1);
+    expect(__builtin_object_size(trailing_1->c, 1), -1);
+    expect(__builtin_object_size(trailing_0->c, 1), -1);
+    expect(__builtin_object_size(trailing_flex->c, 1), -1);
+}
+
+int main(int argc, char *argv[])
+{
+    stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void *)argv[0]);
+
+    return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/strict-flex-array-2.c b/gcc/testsuite/gcc.dg/strict-flex-array-2.c
new file mode 100644
index 000000000000..e474b9ec43fa
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/strict-flex-array-2.c
@@ -0,0 +1,60 @@ 
+/* test the combination of attribute strict_flex_arrays and option
+   -fstrict-flex-arrays: when both attribute and option specified,
+   attribute will have higher priority.  */
+/* { dg-do run } */
+/* { dg-options "-O2 -fstrict-flex-arrays=3" } */
+
+#include <stdio.h>
+
+#define expect(p, _v) do { \
+    size_t v = _v; \
+    if (p == v) \
+        printf("ok:  %s == %zd\n", #p, p); \
+    else \
+	{  \
+          printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
+	  __builtin_abort (); \
+	} \
+} while (0);
+
+struct trailing_array_1 {
+    int a;
+    int b;
+    int c[4] __attribute__ ((strict_flex_arrays (0)));
+};
+
+struct trailing_array_2 {
+    int a;
+    int b;
+    int c[1] __attribute__ ((strict_flex_arrays (1)));
+};
+
+struct trailing_array_3 {
+    int a;
+    int b;
+    int c[0] __attribute__ ((strict_flex_arrays (2)));
+};
+struct trailing_array_4 {
+    int a;
+    int b;
+    int c[];
+};
+
+void __attribute__((__noinline__)) stuff(
+    struct trailing_array_1 *normal,
+    struct trailing_array_2 *trailing_1,
+    struct trailing_array_3 *trailing_0,
+    struct trailing_array_4 *trailing_flex)
+{
+    expect(__builtin_object_size(normal->c, 1), -1);
+    expect(__builtin_object_size(trailing_1->c, 1), -1);
+    expect(__builtin_object_size(trailing_0->c, 1), -1);
+    expect(__builtin_object_size(trailing_flex->c, 1), -1);
+}
+
+int main(int argc, char *argv[])
+{
+    stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void *)argv[0]);
+
+    return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/strict-flex-array-3.c b/gcc/testsuite/gcc.dg/strict-flex-array-3.c
new file mode 100644
index 000000000000..b45e7b32f6d1
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/strict-flex-array-3.c
@@ -0,0 +1,60 @@ 
+/* test the combination of attribute strict_flex_arrays and option
+   -fstrict-flex-arrays: when both attribute and option specified,
+   attribute will have higher priority.  */
+/* { dg-do run } */
+/* { dg-options "-O2 -fstrict-flex-arrays=0" } */
+
+#include <stdio.h>
+
+#define expect(p, _v) do { \
+    size_t v = _v; \
+    if (p == v) \
+        printf("ok:  %s == %zd\n", #p, p); \
+    else \
+	{  \
+          printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
+	  __builtin_abort (); \
+	} \
+} while (0);
+
+struct trailing_array_1 {
+    int a;
+    int b;
+    int c[4] __attribute__ ((strict_flex_arrays (1)));
+};
+
+struct trailing_array_2 {
+    int a;
+    int b;
+    int c[1] __attribute__ ((strict_flex_arrays (2)));
+};
+
+struct trailing_array_3 {
+    int a;
+    int b;
+    int c[0] __attribute__ ((strict_flex_arrays (3)));
+};
+struct trailing_array_4 {
+    int a;
+    int b;
+    int c[];
+};
+
+void __attribute__((__noinline__)) stuff(
+    struct trailing_array_1 *normal,
+    struct trailing_array_2 *trailing_1,
+    struct trailing_array_3 *trailing_0,
+    struct trailing_array_4 *trailing_flex)
+{
+    expect(__builtin_object_size(normal->c, 1), 16);
+    expect(__builtin_object_size(trailing_1->c, 1), 4);
+    expect(__builtin_object_size(trailing_0->c, 1), 0);
+    expect(__builtin_object_size(trailing_flex->c, 1), -1);
+}
+
+int main(int argc, char *argv[])
+{
+    stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void *)argv[0]);
+
+    return 0;
+}
diff --git a/gcc/tree-object-size.cc b/gcc/tree-object-size.cc
index 4eb454a4a33b..1f04cb80fd0a 100644
--- a/gcc/tree-object-size.cc
+++ b/gcc/tree-object-size.cc
@@ -604,9 +604,9 @@  addr_object_size (struct object_size_info *osi, const_tree ptr,
 	  else if (var != pt_var && TREE_CODE (pt_var) == MEM_REF)
 	    {
 	      tree v = var;
-	      /* For &X->fld, compute object size only if fld isn't the last
-		 field, as struct { int i; char c[1]; } is often used instead
-		 of flexible array member.  */
+	      /* For &X->fld, compute object size if fld isn't a flexible array
+		 member.  */
+	      bool is_flexible_array_mem_ref = false;
 	      while (v && v != pt_var)
 		switch (TREE_CODE (v))
 		  {
@@ -633,6 +633,7 @@  addr_object_size (struct object_size_info *osi, const_tree ptr,
 			v = NULL_TREE;
 			break;
 		      }
+		    is_flexible_array_mem_ref = array_at_struct_end_p (v);
 		    while (v != pt_var && TREE_CODE (v) == COMPONENT_REF)
 		      if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
 			  != UNION_TYPE
@@ -645,12 +646,9 @@  addr_object_size (struct object_size_info *osi, const_tree ptr,
 			&& TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
 			   == RECORD_TYPE)
 		      {
-			tree fld_chain = DECL_CHAIN (TREE_OPERAND (v, 1));
-			for (; fld_chain; fld_chain = DECL_CHAIN (fld_chain))
-			  if (TREE_CODE (fld_chain) == FIELD_DECL)
-			    break;
-
-			if (fld_chain)
+			/* compute object size only if v is not a
+			   flexible array member.  */
+			if (!is_flexible_array_mem_ref)
 			  {
 			    v = NULL_TREE;
 			    break;