[PATCH v3 2/2] [PR debug/67192] Further fix C loops' back-jump location

[Andreas Arnez <arnez at linux dot vnet dot ibm dot com>]

After parsing an unconditional "while"- or "for"-loop, the C front-end
generates a backward-goto statement and implicitly sets its location to
the current input_location.  But in some cases the parser peeks ahead
first, such that input_location already points to the line after the
loop and the generated backward-goto gets the wrong line number.

One way this can occur is with a loop body consisting of an "if"
statement, because then the parser peeks for an optional "else" before
finishing the loop.

Another way occurred after r223098 ("Implement
-Wmisleading-indentation"), even with a loop body enclosed in braces.
This was because the check for misleading indentation always peeks ahead
one token as well.

This patch avoids the use of input_location and sets the location of the
backward-goto to the start of the loop body instead, or, if there is no
loop body, to the start of the loop.

gcc/c/ChangeLog:

	PR debug/67192
	* c-typeck.c (c_finish_loop): For unconditional loops, set the
	location of the backward-goto to the start of the loop body.

gcc/testsuite/ChangeLog:

	PR debug/67192
	* gcc.dg/guality/pr67192.c (f3, f4): New functions.
	(main): Invoke them.
---
 gcc/c/c-typeck.c                       | 10 ++++++++++
 gcc/testsuite/gcc.dg/guality/pr67192.c | 26 ++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 2363b9b..e4c3720 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -9878,6 +9878,16 @@ c_finish_loop (location_t start_locus, tree cond, tree incr, tree body,
 	    exit = fold_build3_loc (input_location,
 				COND_EXPR, void_type_node, cond, exit, t);
 	}
+      else
+	{
+	  /* For the backward-goto's location of an unconditional loop
+	     use the beginning of the body, or, if there is none, the
+	     top of the loop.  */
+	  location_t loc = EXPR_LOCATION (expr_first (body));
+	  if (loc == UNKNOWN_LOCATION)
+	    loc = start_locus;
+	  SET_EXPR_LOCATION (exit, loc);
+	}
 
       add_stmt (top);
     }
diff --git a/gcc/testsuite/gcc.dg/guality/pr67192.c b/gcc/testsuite/gcc.dg/guality/pr67192.c
index f6382ef..946e68f 100644
--- a/gcc/testsuite/gcc.dg/guality/pr67192.c
+++ b/gcc/testsuite/gcc.dg/guality/pr67192.c
@@ -39,15 +39,41 @@ f2 (void)
   do_it (); /* { dg-final { gdb-test 39 "cnt" "10" } } */
 }
 
+__attribute__((noinline, noclone)) static void
+f3 (void)
+{
+  for (;; do_it())
+    if (last ())
+      break;
+  do_it (); /* { dg-final { gdb-test 48 "cnt" "15" } } */
+}
+
+__attribute__((noinline, noclone)) static void
+f4 (void)
+{
+  while (1) /* { dg-final { gdb-test 54 "cnt" "15" } } */
+    if (last ())
+      break;
+    else
+      do_it ();
+  do_it (); /* { dg-final { gdb-test 59 "cnt" "20" } } */
+}
+
 void (*volatile fnp1) (void) = f1;
 void (*volatile fnp2) (void) = f2;
+void (*volatile fnp3) (void) = f3;
+void (*volatile fnp4) (void) = f4;
 
 int
 main ()
 {
   asm volatile ("" : : "r" (&fnp1) : "memory");
   asm volatile ("" : : "r" (&fnp2) : "memory");
+  asm volatile ("" : : "r" (&fnp3) : "memory");
+  asm volatile ("" : : "r" (&fnp4) : "memory");
   fnp1 ();
   fnp2 ();
+  fnp3 ();
+  fnp4 ();
   return 0;
 }
-- 
2.3.0