expr: Workaround profiledbootstrap uninit false positive [PR103899]

The threader changes resulted in a false positive warning during
profiledbootstrap:
In file included from ../../gcc/expr.c:26:
../../gcc/tree.h: In function ‘rtx_def* expand_expr_real_1(tree, rtx, machine_mode, expand_modifier, rtx_def**, bool)’:
../../gcc/tree.h:244:56: error: ‘context’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  244 | #define TREE_CODE(NODE) ((enum tree_code) (NODE)->base.code)
      |                                                        ^~~~
../../gcc/expr.c:10343:8: note: ‘context’ was declared here
10343 |   tree context;
      |        ^~~~~~~
While it will be nice to improve the uninit pass to handle it if possible
(I do not want to close the PR until that is done), doing profiledbootstrap
is a common thing to do, so a workaround is handy, especially as in this
case when the workaround seems to be the right thing to do, as it moves
a variable declaration to the only place where it is set and used and avoids
the weird and for uninit asking
  tree context;
...
  if (exp)
    context = ...;
  gcc_assert (!exp
              || use (context)
              || use_some_more (context));

2022-01-06  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/103899
	* expr.c (expand_expr_real_1): Add a workaround for bogus uninit
	warning by moving context variable to the only spot where it is used
	and moving gcc_assert into if body.

1 files changed, 10 insertions, 9 deletions

diff --git a/gcc/expr.c b/gcc/expr.c
index 7fa001f..9fb0187 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -10340,7 +10340,6 @@ expand_expr_real_1 (tree exp, rtx target, machine_mode tmode,
   enum tree_code code = TREE_CODE (exp);
   rtx subtarget, original_target;
   int ignore;
-  tree context;
   bool reduce_bit_field;
   location_t loc = EXPR_LOCATION (exp);
   struct separate_ops ops;
@@ -10579,14 +10578,16 @@ expand_expr_real_1 (tree exp, rtx target, machine_mode tmode,
       /* Variables inherited from containing functions should have
 	 been lowered by this point.  */
       if (exp)
-	context = decl_function_context (exp);
-      gcc_assert (!exp
-		  || SCOPE_FILE_SCOPE_P (context)
-		  || context == current_function_decl
-		  || TREE_STATIC (exp)
-		  || DECL_EXTERNAL (exp)
-		  /* ??? C++ creates functions that are not TREE_STATIC.  */
-		  || TREE_CODE (exp) == FUNCTION_DECL);
+	{
+	  tree context = decl_function_context (exp);
+	  gcc_assert (SCOPE_FILE_SCOPE_P (context)
+		      || context == current_function_decl
+		      || TREE_STATIC (exp)
+		      || DECL_EXTERNAL (exp)
+		      /* ??? C++ creates functions that are not
+			 TREE_STATIC.  */
+		      || TREE_CODE (exp) == FUNCTION_DECL);
+	}
 
       /* This is the case of an array whose size is to be determined
 	 from its initializer, while the initializer is still being parsed.