[PATCH 1/2] analyzer: return a concrete offset for cast_regions

[Tim Lange <mail@tim-lange.me>]

This patch fixes a bug where maybe_fold_sub_svalue did not fold the
access of a single char from a string to a char when the offset was zero
because get_relative_concrete_offset did return false for cast_regions.

Regrtested on Linux x86_64.

2022-09-02  Tim Lange  <mail@tim-lange.me>

gcc/analyzer/ChangeLog:

	* region.cc (cast_region::get_relative_concrete_offset):
	New overloaded method.
	* region.h: Add cast_region::get_relative_concrete_offset.

gcc/testsuite/ChangeLog:

	* gcc.dg/analyzer/fold-string-to-char.c: New test.

---
 gcc/analyzer/region.cc                              | 10 ++++++++++
 gcc/analyzer/region.h                               |  2 ++
 gcc/testsuite/gcc.dg/analyzer/fold-string-to-char.c |  8 ++++++++
 3 files changed, 20 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/analyzer/fold-string-to-char.c

diff --git a/gcc/analyzer/region.cc b/gcc/analyzer/region.cc
index f4aba6b9c88..9c8279b130d 100644
--- a/gcc/analyzer/region.cc
+++ b/gcc/analyzer/region.cc
@@ -1556,6 +1556,16 @@ cast_region::dump_to_pp (pretty_printer *pp, bool simple) const
     }
 }
 
+/* Implementation of region::get_relative_concrete_offset vfunc
+   for cast_region.  */
+
+bool
+cast_region::get_relative_concrete_offset (bit_offset_t *out) const
+{
+  *out = (int) 0;
+  return true;
+}
+
 /* class heap_allocated_region : public region.  */
 
 /* Implementation of region::dump_to_pp vfunc for heap_allocated_region.  */
diff --git a/gcc/analyzer/region.h b/gcc/analyzer/region.h
index d37584b7285..34ce1fa1714 100644
--- a/gcc/analyzer/region.h
+++ b/gcc/analyzer/region.h
@@ -1087,6 +1087,8 @@ public:
   void accept (visitor *v) const final override;
   void dump_to_pp (pretty_printer *pp, bool simple) const final override;
 
+  bool get_relative_concrete_offset (bit_offset_t *out) const final override;
+
   const region *get_original_region () const { return m_original_region; }
 
 private:
diff --git a/gcc/testsuite/gcc.dg/analyzer/fold-string-to-char.c b/gcc/testsuite/gcc.dg/analyzer/fold-string-to-char.c
new file mode 100644
index 00000000000..46139216bba
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/analyzer/fold-string-to-char.c
@@ -0,0 +1,8 @@
+#include "analyzer-decls.h"
+
+void test_1 (void)
+{
+  char str[] = "Hello";
+  char *ptr = str;
+  __analyzer_eval (ptr[0] == 'H'); /* { dg-warning "TRUE" } */
+}
-- 
2.37.2