[PATCH] C FE: use correct location range for static assertions

[David Malcolm]

When issuing diagnostics for _Static_assert, we currently ignore the
location/range of the asserted expression, and instead use the
location/range of the first token within it, which can be
incorrect for compound expressions:

error: expression in static assertion is not constant
   _Static_assert (param > 0, "message");
                   ^~~~~

This patch changes things to use EXPR_LOC_OR_LOC, so we use the
location/range of the expression if it has one, falling back to the old
behavior if it doesn't, giving:

error: expression in static assertion is not constant
   _Static_assert (param > 0, "message");
                   ~~~~~~^~~

Successfully bootstrapped&regrtested on x86_64-pc-linux-gnu

OK for trunk in stage 3?

[a much earlier version of this was posted as part of:
"[PATCH 16/22] C/C++ frontend: use tree ranges in various diagnostics"
  https://gcc.gnu.org/ml/gcc-patches/2015-09/msg00745.html
but this patch bears no resemblence apart from the testcase, due to
changes in representation]

gcc/c/ChangeLog:
        * c-parser.c (c_parser_static_assert_declaration_no_semi): Use the
        expression location, falling back on the first token location,
        rather than always using the latter.

gcc/testsuite/ChangeLog:
        * gcc.dg/diagnostic-range-static-assert.c: New test case.
---
 gcc/c/c-parser.c                                   |  3 ++-
 .../gcc.dg/diagnostic-range-static-assert.c        | 24 ++++++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/diagnostic-range-static-assert.c

diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index 124c30b..5c32f45 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -2097,8 +2097,9 @@ c_parser_static_assert_declaration_no_semi (c_parser 
*parser)
   c_parser_consume_token (parser);
   if (!c_parser_require (parser, CPP_OPEN_PAREN, "expected %<(%>"))
     return;
-  value_loc = c_parser_peek_token (parser)->location;
+  location_t value_tok_loc = c_parser_peek_token (parser)->location;
   value = c_parser_expr_no_commas (parser, NULL).value;
+  value_loc = EXPR_LOC_OR_LOC (value, value_tok_loc);
   parser->lex_untranslated_string = true;
   if (!c_parser_require (parser, CPP_COMMA, "expected %<,%>"))
     {
diff --git a/gcc/testsuite/gcc.dg/diagnostic-range-static-assert.c 
b/gcc/testsuite/gcc.dg/diagnostic-range-static-assert.c
new file mode 100644
index 0000000..6f75476
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/diagnostic-range-static-assert.c
@@ -0,0 +1,24 @@
+/* { dg-options "-fdiagnostics-show-caret" } */
+
+void test_nonconst_static_assert (int param)
+{
+  int local = 0;
+
+  _Static_assert (param > 0, "message"); /* { dg-error "expression in static 
assertion is not constant" } */
+/* { dg-begin-multiline-output "" }
+   _Static_assert (param > 0, "message");
+                   ~~~~~~^~~
+{ dg-end-multiline-output "" } */
+
+  _Static_assert (param, "message"); /* { dg-error "expression in static 
assertion is not constant" } */
+/* { dg-begin-multiline-output "" }
+   _Static_assert (param, "message");
+                   ^~~~~
+{ dg-end-multiline-output "" } */
+
+  _Static_assert (local, "message"); /* { dg-error "expression in static 
assertion is not constant" } */
+/* { dg-begin-multiline-output "" }
+   _Static_assert (local, "message");
+                   ^~~~~
+{ dg-end-multiline-output "" } */
+}
-- 
1.8.5.3