[v4] gcov: Fix "do-while" structure in case statement leads to incorrect code coverage [PR93680]
Commit Message
On 2023/3/9 20:02, Richard Biener wrote:
> On Wed, 8 Mar 2023, Xionghu Luo wrote:
>
>>
>>
>> On 2023/3/7 19:25, Richard Biener wrote:
>>>>> It would be nice to avoid creating blocks / preserving labels we'll
>>>>> immediately remove again. For that we do need some analysis
>>>>> before creating basic-blocks that determines whether a label is
>>>>> possibly reached by a non-falltru edge.
>>>>>
>>>>
>>>> <bb 2> :
>>>> p = 0;
>>>> switch (s) <default: <D.2756>, case 0: <L0>, case 1: <D.2744>>
>>>>
>>>> <bb 3> :
>>>> <L0>: <= prev_stmt
>>>> <D.2748>: <= stmt
>>>> p = p + 1;
>>>> n = n + -1;
>>>> if (n != 0) goto <D.2748>; else goto <D.2746>;
>>>>
>>>> Check if <L0> is a case label and <D.2748> is a goto target then return
>>>> true
>>>> in stmt_starts_bb_p to start a new basic block? This would avoid creating
>>>> and
>>>> removing blocks, but cleanup_dead_labels has all bbs setup while
>>>> stmt_starts_bb_p
>>>> does't yet to iterate bbs/labels to establish label_for_bb[] map?
>>
>>> Yes. I think we'd need something more pragmatic before make_blocks (),
>>> like re-computing TREE_USED of the label decls or computing a bitmap
>>> of targeted labels (targeted by goto, switch or any other means).
>>>
>>> I'll note that doing a cleanup_dead_labels () like optimization before
>>> we create blocks will help keeping LABEL_DECL_UID and thus
>>> label_to_block_map dense. But it does look like a bit of
>>> an chicken-and-egg problem and the question is how effective the
>>> dead label removal is in practice.
>>
>> Tried to add function compute_target_labels(not sure whether the function
>> name is suitable) in the front of make_blocks_1, now the fortran case doesn't
>> create/removing blocks now, but I still have several questions:
>>
>> 1. I used hash_set<tree> to save the target labels instead of bitmap, as
>> labels
>> are tree type value instead of block index so bitmap is not good for it since
>> we don't have LABEL_DECL_UID now?
>
> We don't have LABEL_DECL_UID, we have DECL_UID though, but the choice of
> hash_set<tree> vs. bitmap is somewhat arbitrary here. The real cost is
> the extra walk over all stmts.
>
>> 2. Is the compute_target_labels still only for !optimize? And if we compute
>> the target labels before create bbs, it is unnessary to guard the first
>> cleanup_dead_labels under !optimize now, because the switch-case-do-while
>> case already create new block for CASE_LABEL already.
>
> OK.
>
>> 3. I only added GIMPLE_SWITCH/GIMPLE_COND in compute_target_labels
>> so far, is it needed to also handle GIMPLE_ASM/GIMPLE_TRANSACTION and even
>> labels_eh?
>
> I'd add GIMPLE_ASM handling, the rest should be OK wrt debugging and
> coverage already?
>
>> PS1: The v3 patch will cause one test case fail:
>>
>> Number of regressions in total: 1
>>> FAIL: gcc.c-torture/compile/limits-caselabels.c -O0 (test for excess
>>> errors)
>>
>> due to this exausting case has labels from L0 to L100001, they won't be
>> optimized
>> to a simple if-else expression like before...
>
> Hmm, that's somewhat unexpected.
>
>>
>> PS2: The GIMPLE_GOTO piece of code would cause some fortran cases run fail due
>> to __builtin_unreachable trap generated in .fixup_cfg1, I didn't dig into it
>> so
>> just skip these label...
>
> Please investigate, we might be missing a corner case here.
>
I think the *previous fix* for labels “in the middle of block” is *incorrect*, it should
be handled in make_edges_bb when a basic block only has Label in it, just create a
fallthrough edge for it to avoid wrong cfg and unreachable trap generated?
@@ -853,6 +922,12 @@ make_edges_bb (basic_block bb, struct omp_region **pcur_region, int *pomp_index)
bool fallthru = false;
int ret = 0;
+ if (!optimize && !last)
+ {
+ make_edge (bb, bb->next_bb, EDGE_FALLTHRU);
+ return 0;
+ }
+
if (!last)
return ret;
With the fix, the attached version could pass bootstrap and regression test on x86_64-linux-gnu.
From ec505cc7952707db805802af83dd82776a1d949f Mon Sep 17 00:00:00 2001
From: Xionghu Luo <xionghuluo@tencent.com>
Date: Tue, 28 Feb 2023 17:46:18 +0800
Subject: [PATCH v4] gcov: Fix "do-while" structure in case statement leads to
incorrect code coverage [PR93680]
v4: Address comments.
4.1. Handle GIMPLE_GOTO and GIMPLE_ASM.
4.2. Fix failure of limit-caselabels.c (labels on same line),
pointer_array_1.f90 (unused labels) etc.
v3: Add compute_target_labels and call it in the front of make_blocks_1.
v2: Check whether two locus are on same line.
Start a new basic block if two labels have different location when
test-coverage.
Regression tested pass on x86_64-linux-gnu and aarch64-linux-gnu, OK for
master?
gcc/ChangeLog:
PR gcov/93680
* tree-cfg.cc (stmt_starts_bb_p): Check whether the label is in
target_labels.
(compute_target_labels): New function.
(make_blocks_1): Call compute_target_labels.
(same_line_p): Return false if two locus are both
UNKOWN_LOCATION.
gcc/testsuite/ChangeLog:
PR gcov/93680
* g++.dg/gcov/gcov-1.C: Correct counts.
* gcc.misc-tests/gcov-4.c: Likewise.
* gcc.misc-tests/gcov-pr85332.c: Likewise.
* lib/gcov.exp: Also clean gcda if fail.
* gcc.misc-tests/gcov-pr93680.c: New test.
Signed-off-by: Xionghu Luo <xionghuluo@tencent.com>
---
gcc/tree-cfg.cc | 97 ++++++++++++++++++++-
gcc/testsuite/g++.dg/gcov/gcov-1.C | 2 +-
gcc/testsuite/gcc.misc-tests/gcov-4.c | 2 +-
gcc/testsuite/gcc.misc-tests/gcov-pr85332.c | 2 +-
gcc/testsuite/gcc.misc-tests/gcov-pr93680.c | 24 +++++
gcc/testsuite/lib/gcov.exp | 4 +-
6 files changed, 122 insertions(+), 9 deletions(-)
create mode 100644 gcc/testsuite/gcc.misc-tests/gcov-pr93680.c
@@ -164,7 +164,7 @@ static edge gimple_redirect_edge_and_branch (edge, basic_block);
static edge gimple_try_redirect_by_replacing_jump (edge, basic_block);
/* Various helpers. */
-static inline bool stmt_starts_bb_p (gimple *, gimple *);
+static inline bool stmt_starts_bb_p (gimple *, gimple *, hash_set<tree> *);
static int gimple_verify_flow_info (void);
static void gimple_make_forwarder_block (edge);
static gimple *first_non_label_stmt (basic_block);
@@ -521,6 +521,68 @@ gimple_call_initialize_ctrl_altering (gimple *stmt)
gimple_call_set_ctrl_altering (stmt, false);
}
+/* Compute target labels to save useful labels. */
+static void
+compute_target_labels (gimple_seq seq, hash_set<tree> *target_labels)
+{
+ gimple *stmt = NULL;
+ gimple_stmt_iterator j = gsi_start (seq);
+
+ while (!gsi_end_p (j))
+ {
+ stmt = gsi_stmt (j);
+
+ switch (gimple_code (stmt))
+ {
+ case GIMPLE_COND:
+ {
+ gcond *cstmt = as_a <gcond *> (stmt);
+ tree true_label = gimple_cond_true_label (cstmt);
+ tree false_label = gimple_cond_false_label (cstmt);
+ target_labels->add (true_label);
+ target_labels->add (false_label);
+ }
+ break;
+ case GIMPLE_SWITCH:
+ {
+ gswitch *gstmt = as_a <gswitch *> (stmt);
+ size_t i, n = gimple_switch_num_labels (gstmt);
+ tree elt, label;
+ for (i = 0; i < n; i++)
+ {
+ elt = gimple_switch_label (gstmt, i);
+ label = CASE_LABEL (elt);
+ target_labels->add (label);
+ }
+ }
+ break;
+ case GIMPLE_GOTO:
+ if (!computed_goto_p (stmt))
+ {
+ tree dest = gimple_goto_dest (stmt);
+ target_labels->add (dest);
+ }
+ break;
+ case GIMPLE_ASM:
+ {
+ gasm *asm_stmt = as_a <gasm *> (stmt);
+ int i, n = gimple_asm_nlabels (asm_stmt);
+ for (i = 0; i < n; ++i)
+ {
+ tree cons = gimple_asm_label_op (asm_stmt, i);
+ target_labels->add (cons);
+ }
+ }
+ break;
+
+ default:
+ break;
+ }
+
+ gsi_next (&j);
+ }
+}
+
/* Insert SEQ after BB and build a flowgraph. */
@@ -532,6 +594,10 @@ make_blocks_1 (gimple_seq seq, basic_block bb)
gimple *prev_stmt = NULL;
bool start_new_block = true;
bool first_stmt_of_seq = true;
+ hash_set<tree> target_labels;
+
+ if (!optimize)
+ compute_target_labels (seq, &target_labels);
while (!gsi_end_p (i))
{
@@ -553,7 +619,7 @@ make_blocks_1 (gimple_seq seq, basic_block bb)
/* If the statement starts a new basic block or if we have determined
in a previous pass that we need to create a new block for STMT, do
so now. */
- if (start_new_block || stmt_starts_bb_p (stmt, prev_stmt))
+ if (start_new_block || stmt_starts_bb_p (stmt, prev_stmt, &target_labels))
{
if (!first_stmt_of_seq)
gsi_split_seq_before (&i, &seq);
@@ -566,6 +632,9 @@ make_blocks_1 (gimple_seq seq, basic_block bb)
codes. */
gimple_set_bb (stmt, bb);
+ if (!optimize && gimple_code (stmt) == GIMPLE_LABEL)
+ target_labels.add (gimple_label_label (as_a<glabel *> (stmt)));
+
/* If STMT is a basic block terminator, set START_NEW_BLOCK for the
next iteration. */
if (stmt_ends_bb_p (stmt))
@@ -853,6 +922,12 @@ make_edges_bb (basic_block bb, struct omp_region **pcur_region, int *pomp_index)
bool fallthru = false;
int ret = 0;
+ if (!optimize && !last)
+ {
+ make_edge (bb, bb->next_bb, EDGE_FALLTHRU);
+ return 0;
+ }
+
if (!last)
return ret;
@@ -1152,6 +1227,10 @@ same_line_p (location_t locus1, expanded_location *from, location_t locus2)
{
expanded_location to;
+ if (LOCATION_LOCUS (locus1) == UNKNOWN_LOCATION
+ && LOCATION_LOCUS (locus2) == UNKNOWN_LOCATION)
+ return false;
+
if (locus1 == locus2)
return true;
@@ -2832,7 +2911,8 @@ simple_goto_p (gimple *t)
label. */
static inline bool
-stmt_starts_bb_p (gimple *stmt, gimple *prev_stmt)
+stmt_starts_bb_p (gimple *stmt, gimple *prev_stmt,
+ hash_set<tree> *target_labels)
{
if (stmt == NULL)
return false;
@@ -2860,6 +2940,17 @@ stmt_starts_bb_p (gimple *stmt, gimple *prev_stmt)
|| !DECL_ARTIFICIAL (gimple_label_label (plabel)))
return true;
+ location_t prev_locus = gimple_location (plabel);
+ location_t locus = gimple_location (label_stmt);
+ expanded_location locus_e = expand_location (locus);
+
+ if (!optimize
+ && target_labels->contains (gimple_label_label (label_stmt))
+ && (LOCATION_LOCUS (locus) != UNKNOWN_LOCATION
+ || LOCATION_LOCUS (prev_locus) != UNKNOWN_LOCATION)
+ && !same_line_p (locus, &locus_e, prev_locus))
+ return true;
+
cfg_stats.num_merged_labels++;
return false;
}
@@ -263,7 +263,7 @@ test_switch (int i, int j)
case 2:
result = do_something (1024);
break;
- case 3: /* count(3) */
+ case 3: /* count(2) */
case 4:
/* branch(67) */
if (j == 2) /* count(3) */
@@ -122,7 +122,7 @@ top:
}
else
{
-else_: /* count(1) */
+else_: /* count(2) */
j = do_something (j); /* count(2) */
if (j) /* count(2) */
{
@@ -7,7 +7,7 @@ int doit(int sel, int n, void *p)
switch (sel)
{
- case 0: /* count(3) */
+ case 0: /* count(1) */
do {*p0 += *p0;} while (--n); /* count(3) */
return *p0 == 0; /* count(1) */
new file mode 100644
@@ -0,0 +1,24 @@
+/* { dg-options "-fprofile-arcs -ftest-coverage" } */
+/* { dg-do run { target native } } */
+
+int f(int s, int n)
+{
+ int p = 0;
+
+ switch (s)
+ {
+ case 0: /* count(1) */
+ do { p++; } while (--n); /* count(5) */
+ return p; /* count(1) */
+
+ case 1: /* count(1) */
+ do { p++; } while (--n); /* count(5) */
+ return p; /* count(1) */
+ }
+
+ return 0;
+}
+
+int main() { f(0, 5); f(1, 5); return 0; }
+
+/* { dg-final { run-gcov gcov-pr93680.c } } */
@@ -424,9 +424,7 @@ proc run-gcov { args } {
}
if { $tfailed > 0 } {
fail "$testname gcov: $lfailed failures in line counts, $bfailed in branch percentages, $cfailed in return percentages, $ifailed in intermediate format"
- if { $xfailed } {
- clean-gcov $testcase
- }
+ clean-gcov $testcase
} else {
pass "$testname gcov"
clean-gcov $testcase