Fix ICE for missing header fix-it hints with overlarge #line directives (PR c/84852)

PR c/84852 reports an ICE inside diagnostic_show_locus when printing
a diagnostic for a source file with a #line >= 2^31:

  #line 7777777777
  int foo (void) { return strlen(""); }

where we're attempting to print a fix-it hint at the top of the file
and underline the "strlen" (two "line spans").

The
  #line 7777777777
won't fix within the 32-bit linenum_type, and is truncated from
  0x1cf977871
to
   0xcf977871
i.e. 3482810481 in decimal.

Such a #line is reported by -pedantic and -pedantic-errors, but we
shouldn't ICE.

The ICE is an assertion failure within layout::calculate_line_spans,
where the line spans have not been properly sorted.

The layout_ranges are stored as int, rather than linenum_type,
giving line -812156815 for the error, and line 1 for the fix-it hint.

However, line_span uses linenum_type rather than int.

line_span::comparator compares these values as int, and hence
decides that (linenum_type)3482810481 aka (int)-812156815 is less
than line 1.

This leads to this assertion failing in layout::calculate_line_spans:

1105	      gcc_assert (next->m_first_line >= current->m_first_line);

since it isn't the case that 1 >= 3482810481.

The underlying problem is the mix of types for storing line numbers:
in parts of libcpp and diagnostic-show-locus.c we use linenum_type;
in other places (including libcpp's expanded_location) we use int.

I looked at using linenum_type throughout, but doing so turned into
a large patch, so this patch fixes the ICE in a less invasive way
by merely using linenum_type more consistently just within
diagnostic-show-locus.c, and fixing line_span::comparator to properly
handle line numbers (and line number differences) >= 2^31, by using
a new helper function for linenum_type differences, computing the
difference using long long, and using the sign of the difference
(as the difference might not fit in the "int" return type imposed
by qsort).

gcc/ChangeLog:
	PR c/84852
	* diagnostic-show-locus.c (class layout_point): Convert m_line
	from int to linenum_type.
	(line_span::comparator): Use linenum "compare" function when
	comparing line numbers.
	(test_line_span): New function.
	(layout_range::contains_point): Convert param "row" from int to
	linenum_type.
	(layout_range::intersects_line_p): Likewise.
	(layout::will_show_line_p): Likewise.
	(layout::print_source_line): Likewise.
	(layout::should_print_annotation_line_p): Likewise.
	(layout::print_annotation_line): Likewise.
	(layout::print_leading_fixits): Likewise.
	(layout::annotation_line_showed_range_p): Likewise.
	(struct line_corrections): Likewise for field m_row.
	(line_corrections::line_corrections): Likewise for param "row".
	(layout::print_trailing_fixits): Likewise.
	(layout::get_state_at_point): Likewise.
	(layout::get_x_bound_for_row): Likewise.
	(layout::print_line): Likewise.
	(diagnostic_show_locus): Likewise for locals "last_line" and
	"row".
	(selftest::diagnostic_show_locus_c_tests): Call test_line_span.
	* input.c (selftest::test_linenum_comparisons): New function.
	(selftest::input_c_tests): Call it.
	* selftest.c (selftest::test_assertions): Test ASSERT_GT,
	ASSERT_GT_AT, ASSERT_LT, and ASSERT_LT_AT.
	* selftest.h (ASSERT_GT): New macro.
	(ASSERT_GT_AT): New macro.
	(ASSERT_LT): New macro.
	(ASSERT_LT_AT): New macro.

gcc/testsuite/ChangeLog:
	PR c/84852
	* gcc.dg/fixits-pr84852-1.c: New test.
	* gcc.dg/fixits-pr84852-2.c: New test.

libcpp/ChangeLog:
	* include/line-map.h (compare): New function on linenum_type.

From-SVN: r258526

2 files changed, 16 insertions, 0 deletions

diff --git a/libcpp/ChangeLog b/libcpp/ChangeLog
index 791c364..a66948f 100644
--- a/libcpp/ChangeLog
+++ b/libcpp/ChangeLog
@@ -1,3 +1,7 @@
+2018-03-14  David Malcolm  <dmalcolm@redhat.com>
+
+	* include/line-map.h (compare): New function on linenum_type.
+
 2018-02-28  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR preprocessor/84517
diff --git a/libcpp/include/line-map.h b/libcpp/include/line-map.h
index f6242fc..d6cf816 100644
--- a/libcpp/include/line-map.h
+++ b/libcpp/include/line-map.h
@@ -49,6 +49,18 @@ along with this program; see the file COPYING3.  If not see
 /* The type of line numbers.  */
 typedef unsigned int linenum_type;
 
+/* A function for for use by qsort for comparing line numbers.  */
+
+inline int compare (linenum_type lhs, linenum_type rhs)
+{
+  /* Avoid truncation issues by using long long for the comparison,
+     and only consider the sign of the result.  */
+  long long diff = (long long)lhs - (long long)rhs;
+  if (diff)
+    return diff > 0 ? 1 : -1;
+  return 0;
+}
+
 /* Reason for creating a new line map with linemap_add.  LC_ENTER is
    when including a new file, e.g. a #include directive in C.
    LC_LEAVE is when reaching a file's end.  LC_RENAME is when a file