PR c++/72803 describes an issue where a fix-it hint is to be emitted at
column 512 of a 511-column source line, leading to an ICE.
The root cause is a bug in linemap_line_start, when transitioning from
lines >= 512 in width to narrow lines.
The wide line in the reproducer has a line map with:
m_column_and_range_bits = 15, m_range_bits = 5
giving 10 effective bits for representing columns, so that columns <= 1023
can be represented.
When parsing the following line,
linemap_line_start (..., ..., max_column_hint=0);
is called. This leads to the "add_map" logic, due to this condition:
|| (max_column_hint <= 80 && effective_column_bits >= 10)
i.e. the new line is sufficiently narrower than the old one to
potentially use a new linemap (so as to conserve values within the
location_t space).
It then attempts to avoid allocating a new line map. Part of the logic
to determine if we really need a new line map is this condition:
SOURCE_COLUMN (map, highest) >= (1U << column_bits)
The above condition is incorrect: we need to determine if the highest
column we've handed out will fit within the proposed *effective* column
bits, but "column_bits" here is the column plus the range bits, rather
than just the column bits.
Hence in this case linemap_line_start erroneously decides that we don't
need a new line map, and updates the column bits within the existing
line map, so any location_t values we've already handed out within it
that are offset from the start by
>= (1<<new_column_and_range_bits)
effectively change meaning, leading to incorrect line&column information
when decoding them, and various "interesting" ways for the linemap
code to fail.
The fix is to use the effective column bits in the above conditional.
Successfully bootstrapped®rtested on x86_64-pc-linux-gnu;
adds 9 PASS results to g++.sum.
Committed to trunk as r244199.
gcc/ChangeLog:
PR c++/72803
* input.c (selftest::test_accessing_ordinary_linemaps): Verify
that the transition from a max line width >= 1<<10 to narrower
lines works correctly.
gcc/testsuite/ChangeLog:
PR c++/72803
* g++.dg/diagnostic/pr72803.C: New test case.
libcpp/ChangeLog:
PR c++/72803
* line-map.c (linemap_line_start): When determining if the highest
column given out so far will fit into a proposed change to the
current map, use the effective number of column bits, rather than
the total number of column + range bits.
---
gcc/input.c | 12 ++++++++++++
gcc/testsuite/g++.dg/diagnostic/pr72803.C | 9 +++++++++
libcpp/line-map.c | 2 +-
3 files changed, 22 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/diagnostic/pr72803.C
diff --git a/gcc/input.c b/gcc/input.c
index 22cc74c..4df47f2 100644
--- a/gcc/input.c
+++ b/gcc/input.c
@@ -1688,6 +1688,17 @@ test_accessing_ordinary_linemaps (const line_table_case
&case_)
linemap_line_start (line_table, 3, 2000);
location_t loc_e = linemap_position_for_column (line_table, 700);
+ /* Transitioning back to a short line. */
+ linemap_line_start (line_table, 4, 0);
+ location_t loc_back_to_short = linemap_position_for_column (line_table, 100);
+
+ if (should_have_column_data_p (loc_back_to_short))
+ {
+ /* Verify that we switched to short lines in the linemap. */
+ line_map_ordinary *map = LINEMAPS_LAST_ORDINARY_MAP (line_table);
+ ASSERT_EQ (7, map->m_column_and_range_bits - map->m_range_bits);
+ }
+
linemap_add (line_table, LC_LEAVE, false, NULL, 0);
/* Multiple files. */
@@ -1702,6 +1713,7 @@ test_accessing_ordinary_linemaps (const line_table_case
&case_)
assert_loceq ("foo.c", 2, 1, loc_c);
assert_loceq ("foo.c", 2, 17, loc_d);
assert_loceq ("foo.c", 3, 700, loc_e);
+ assert_loceq ("foo.c", 4, 100, loc_back_to_short);
assert_loceq ("bar.c", 1, 150, loc_f);
ASSERT_FALSE (is_location_from_builtin_token (loc_a));
diff --git a/gcc/testsuite/g++.dg/diagnostic/pr72803.C
b/gcc/testsuite/g++.dg/diagnostic/pr72803.C
new file mode 100644
index 0000000..0a9a390
--- /dev/null
+++ b/gcc/testsuite/g++.dg/diagnostic/pr72803.C
@@ -0,0 +1,9 @@
+/* Long line, with a close brace at column 511, hence with the insertion
+ point for the missing semicolon at column 512. */
+class test {
}
+# 1 "" 1
+// The line directive appears to be necessary to trigger the ICE
+// { dg-error "style of line directive is a GCC extension" "" { target *-*-* }
.-2 }
+
+/* Verify that we get the correct line and column for the diagnostic. */
+// { dg-error "512: expected .;. after class definition" "" { target *-*-* } 3
}
diff --git a/libcpp/line-map.c b/libcpp/line-map.c
index 77beaff..b410c00 100644
--- a/libcpp/line-map.c
+++ b/libcpp/line-map.c
@@ -752,7 +752,7 @@ linemap_line_start (struct line_maps *set, linenum_type
to_line,
single line we can sometimes just increase its column_bits instead. */
if (line_delta < 0
|| last_line != ORDINARY_MAP_STARTING_LINE_NUMBER (map)
- || SOURCE_COLUMN (map, highest) >= (1U << column_bits)
+ || SOURCE_COLUMN (map, highest) >= (1U << (column_bits - range_bits))
|| range_bits < map->m_range_bits)
map = linemap_check_ordinary
(const_cast <line_map *>
--
1.8.5.3
