[gcc r13-6420] analyzer: fix uninit false +ves reading from DECL_HARD_REGISTER [PR108968]

[David Malcolm <dmalcolm@gcc.gnu.org>]

https://gcc.gnu.org/g:20bd258d0fa09837b3a93478ef92d8789cbcd442

commit r13-6420-g20bd258d0fa09837b3a93478ef92d8789cbcd442
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Thu Mar 2 14:01:19 2023 -0500

    analyzer: fix uninit false +ves reading from DECL_HARD_REGISTER [PR108968]
    
    gcc/analyzer/ChangeLog:
            PR analyzer/108968
            * region-model.cc (region_model::get_rvalue_1): Handle VAR_DECLs
            with a DECL_HARD_REGISTER by returning UNKNOWN.
    
    gcc/testsuite/ChangeLog:
            PR analyzer/108968
            * gcc.dg/analyzer/uninit-pr108968-register.c: New test.
    
    Signed-off-by: David Malcolm <dmalcolm@redhat.com>

Diff:
---
 gcc/analyzer/region-model.cc                             | 9 ++++++++-
 gcc/testsuite/gcc.dg/analyzer/uninit-pr108968-register.c | 9 +++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc
index 2187aecbe91..bf07cec2884 100644
--- a/gcc/analyzer/region-model.cc
+++ b/gcc/analyzer/region-model.cc
@@ -2203,9 +2203,16 @@ region_model::get_rvalue_1 (path_var pv, region_model_context *ctxt) const
 	return get_rvalue_for_bits (TREE_TYPE (expr), reg, bits, ctxt);
       }
 
-    case SSA_NAME:
     case VAR_DECL:
+      if (DECL_HARD_REGISTER (pv.m_tree))
+	{
+	  /* If it has a hard register, it doesn't have a memory region
+	     and can't be referred to as an lvalue.  */
+	  return m_mgr->get_or_create_unknown_svalue (TREE_TYPE (pv.m_tree));
+	}
+      /* Fall through. */
     case PARM_DECL:
+    case SSA_NAME:
     case RESULT_DECL:
     case ARRAY_REF:
       {
diff --git a/gcc/testsuite/gcc.dg/analyzer/uninit-pr108968-register.c b/gcc/testsuite/gcc.dg/analyzer/uninit-pr108968-register.c
new file mode 100644
index 00000000000..a76c09e7b14
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/analyzer/uninit-pr108968-register.c
@@ -0,0 +1,9 @@
+/* { dg-do compile { target x86_64-*-* } } */
+
+#define STACK_SIZE 4096
+struct cpu_info {};
+struct cpu_info *get_cpu_info(void)
+{
+  register unsigned long sp asm("rsp");
+  return (struct cpu_info *)((sp | (STACK_SIZE - 1)) + 1) - 1; /* { dg-bogus "use of uninitialized value 'sp'" } */
+}