[gcc r13-5762] analyzer: fix further overzealous state purging [PR108733]

[gcc r13-5762] analyzer: fix further overzealous state purging [PR108733]

[David Malcolm]

https://gcc.gnu.org/g:125b57aa67400388a496c2c0c40d9c8c55e0c94a

commit r13-5762-g125b57aa67400388a496c2c0c40d9c8c55e0c94a
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Thu Feb 9 17:09:51 2023 -0500

    analyzer: fix further overzealous state purging [PR108733]
    
    PR analyzer/108733 reports various false positives in qemu from
    -Wanalyzer-use-of-uninitialized-value with __attribute__((cleanup))
    at -O1 and above.
    
    Root cause is that the state-purging code was failing to treat:
       _25 = MEM[(void * *)&val];
    as a usage of "val", leading to it erroneously purging the
    initialization of "val" along an execution path that didn't otherwise
    use "val", apart from the  __attribute__((cleanup)).
    
    Fixed thusly.
    
    Integration testing on the patch show this change in the number of
    diagnostics:
      -Wanalyzer-use-of-uninitialized-value
           coreutils-9.1: 18 -> 16 (-2)
              qemu-7.2.0: 87 -> 80 (-7)
    where all that I investigated appear to have been false positives, hence
    an improvement.
    
    gcc/analyzer/ChangeLog:
            PR analyzer/108733
            * state-purge.cc (get_candidate_for_purging): Add ADDR_EXPR
            and MEM_REF.
    
    gcc/testsuite/ChangeLog:
            PR analyzer/108733
            * gcc.dg/analyzer/torture/uninit-pr108733.c: New test.
    
    Signed-off-by: David Malcolm <dmalcolm@redhat.com>

Diff:
---
 gcc/analyzer/state-purge.cc                        |  2 +
 .../gcc.dg/analyzer/torture/uninit-pr108733.c      | 65 ++++++++++++++++++++++
 2 files changed, 67 insertions(+)

diff --git a/gcc/analyzer/state-purge.cc b/gcc/analyzer/state-purge.cc
index 5f2d1f7fefa..3a73146d928 100644
--- a/gcc/analyzer/state-purge.cc
+++ b/gcc/analyzer/state-purge.cc
@@ -63,6 +63,8 @@ get_candidate_for_purging (tree node)
       default:
 	return NULL_TREE;
 
+      case ADDR_EXPR:
+      case MEM_REF:
       case COMPONENT_REF:
 	iter = TREE_OPERAND (iter, 0);
 	continue;
diff --git a/gcc/testsuite/gcc.dg/analyzer/torture/uninit-pr108733.c b/gcc/testsuite/gcc.dg/analyzer/torture/uninit-pr108733.c
new file mode 100644
index 00000000000..9e684bf4f09
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/analyzer/torture/uninit-pr108733.c
@@ -0,0 +1,65 @@
+#define NULL ((void*)0)
+
+typedef unsigned char __uint8_t;
+typedef __uint8_t uint8_t;
+typedef char gchar;
+typedef void* gpointer;
+
+extern void g_free(gpointer mem);
+extern gchar* g_strdup(const gchar* str) __attribute__((__malloc__));
+
+static inline void
+g_autoptr_cleanup_generic_gfree(void* p)
+{
+  void** pp = (void**)p;
+  g_free(*pp); /* { dg-bogus "use of uninitialized value" } */
+}
+
+typedef struct Object Object;
+
+void
+error_setg_internal(const char* fmt,
+		    ...) __attribute__((__format__(gnu_printf, 1, 2)));
+void
+visit_type_str(const char* name, char** obj);
+typedef struct SpaprMachineState SpaprMachineState;
+
+extern uint8_t
+spapr_get_cap(SpaprMachineState* spapr, int cap);
+
+typedef struct SpaprCapPossible
+{
+  int num;
+  /* [...snip...] */
+  const char* vals[];
+} SpaprCapPossible;
+
+typedef struct SpaprCapabilityInfo
+{
+  const char* name;
+  /* [...snip...] */
+  int index;
+  /* [...snip...] */
+  SpaprCapPossible* possible;
+  /* [...snip...] */
+} SpaprCapabilityInfo;
+
+void
+spapr_cap_get_string(SpaprMachineState* spapr,
+		     const char* name,
+		     SpaprCapabilityInfo* cap)
+{
+  __attribute__((cleanup(g_autoptr_cleanup_generic_gfree))) char* val = NULL;
+  uint8_t value = spapr_get_cap(spapr, cap->index);
+
+  if (value >= cap->possible->num) {
+    error_setg_internal("Invalid value (%d) for cap-%s",
+			value,
+			cap->name);
+    return;
+  }
+
+  val = g_strdup(cap->possible->vals[value]);
+
+  visit_type_str(name, &val);
+}