[PATCH] tree-optimization/101573 - improve uninit warning at -O0
Richard Biener
rguenther@suse.de
Thu Jul 22 12:34:16 GMT 2021
We can improve uninit warnings from the early pass by looking
at PHI arguments on fallthru edges that are uninitialized and
have uses that are before a possible loop exit. This catches
some cases earlier that we'd only warn in a more confusing
way after early inlining as seen by testcase adjustments.
It introduces
FAIL: gcc.dg/uninit-23.c (test for excess errors)
where we additionally warn
gcc.dg/uninit-23.c:21:13: warning: 't4' is used uninitialized [-Wuninitialized]
which I think is OK even if it's not obvious that the new
warning is an improvement when you look at the obvious source.
Somehow for all cases I never get the `'foo' was declared here`
notes, I didn't dig why that happens but it's odd.
Bootstrapped and tested on x86_64-unknown-linux-gnu.
Any comments?
Thanks,
Richard.
2021-07-22 Richard Biener <rguenther@suse.de>
PR tree-optimization/101573
* tree-ssa-uninit.c (warn_uninitialized_vars): Look at
uninitialized PHI arg defs in some constrained cases.
(execute_early_warn_uninitialized): Calculate dominators.
* gcc.dg/uninit-pr101573.c: New testcase.
* gcc.dg/uninit-15-O0.c: Adjust.
* gcc.dg/uninit-15.c: Likewise.
* gcc.dg/uninit-23.c: Likewise.
* c-c++-common/uninit-17.c: Likewise.
---
gcc/testsuite/c-c++-common/uninit-17.c | 6 +--
gcc/testsuite/gcc.dg/uninit-15-O0.c | 2 +-
gcc/testsuite/gcc.dg/uninit-15.c | 10 ++--
gcc/testsuite/gcc.dg/uninit-23.c | 2 +-
gcc/testsuite/gcc.dg/uninit-pr101573.c | 10 ++++
gcc/tree-ssa-uninit.c | 66 ++++++++++++++++++++++++++
6 files changed, 86 insertions(+), 10 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/uninit-pr101573.c
diff --git a/gcc/testsuite/c-c++-common/uninit-17.c b/gcc/testsuite/c-c++-common/uninit-17.c
index fd773da78ad..b5495366c5b 100644
--- a/gcc/testsuite/c-c++-common/uninit-17.c
+++ b/gcc/testsuite/c-c++-common/uninit-17.c
@@ -9,11 +9,11 @@ static void bar(int a, int *ptr)
{
do
{
- int b; /* { dg-message "declared" } */
+ int b;
if (b < 40) {
- ptr[0] = b; /* { dg-warning "may be used uninitialized" } */
+ ptr[0] = b;
}
- b += 1;
+ b += 1; /* { dg-warning "is used uninitialized" } */
ptr++;
}
while (--a != 0);
diff --git a/gcc/testsuite/gcc.dg/uninit-15-O0.c b/gcc/testsuite/gcc.dg/uninit-15-O0.c
index a3fd2b63ba7..36d96348617 100644
--- a/gcc/testsuite/gcc.dg/uninit-15-O0.c
+++ b/gcc/testsuite/gcc.dg/uninit-15-O0.c
@@ -15,6 +15,6 @@ void baz();
void bar()
{
int j; /* { dg-message "was declared here" {} { xfail *-*-* } } */
- for (; foo(j); ++j)
+ for (; foo(j); ++j) /* { dg-warning "is used uninitialized" } */
baz();
}
diff --git a/gcc/testsuite/gcc.dg/uninit-15.c b/gcc/testsuite/gcc.dg/uninit-15.c
index 8ee10c27aba..85cb116f349 100644
--- a/gcc/testsuite/gcc.dg/uninit-15.c
+++ b/gcc/testsuite/gcc.dg/uninit-15.c
@@ -1,7 +1,7 @@
/* PR tree-optimization/17506
- We issue an uninitialized variable warning at a wrong location at
+ We used to issue an uninitialized variable warning at a wrong location at
line 11, which is very confusing. Make sure we print out a note to
- make it less confusing. (not xfailed alternative)
+ make it less confusing. (xfailed alternative)
But it is of course ok if we warn in bar about uninitialized use
of j. (not xfailed alternative) */
/* { dg-do compile } */
@@ -10,7 +10,7 @@
inline int
foo (int i)
{
- if (i) /* { dg-warning "used uninitialized" } */
+ if (i) /* { dg-warning "used uninitialized" "" { xfail *-*-* } } */
return 1;
return 0;
}
@@ -20,7 +20,7 @@ void baz (void);
void
bar (void)
{
- int j; /* { dg-message "note: 'j' was declared here" "" } */
- for (; foo (j); ++j) /* { dg-warning "'j' is used uninitialized" "" { xfail *-*-* } } */
+ int j; /* { dg-message "note: 'j' was declared here" "" { xfail *-*-* } } */
+ for (; foo (j); ++j) /* { dg-warning "'j' is used uninitialized" } */
baz ();
}
diff --git a/gcc/testsuite/gcc.dg/uninit-23.c b/gcc/testsuite/gcc.dg/uninit-23.c
index d64eb7d2ee9..87b4e989b53 100644
--- a/gcc/testsuite/gcc.dg/uninit-23.c
+++ b/gcc/testsuite/gcc.dg/uninit-23.c
@@ -18,7 +18,7 @@ ql (void)
int *t4 = go; /* { dg-warning "is used uninitialized" } */
l1:
- *t4 = (*t4 != 0) ? 0 : 2;
+ *t4 = (*t4 != 0) ? 0 : 2; /* { dg-warning "is used uninitialized" } */
}
if (ij != 0)
diff --git a/gcc/testsuite/gcc.dg/uninit-pr101573.c b/gcc/testsuite/gcc.dg/uninit-pr101573.c
new file mode 100644
index 00000000000..a574844b791
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/uninit-pr101573.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O0 -Wuninitialized" } */
+
+int main(int argc, char **argv)
+{
+ int a;
+ for(; a < 5; ++a) /* { dg-warning "is used uninitialized" } */
+ ;
+ return 0;
+}
diff --git a/gcc/tree-ssa-uninit.c b/gcc/tree-ssa-uninit.c
index 148f3c2b31d..2ee4edf353f 100644
--- a/gcc/tree-ssa-uninit.c
+++ b/gcc/tree-ssa-uninit.c
@@ -652,6 +652,71 @@ warn_uninitialized_vars (bool wmaybe_uninit)
{
basic_block succ = single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun));
wlims.always_executed = dominated_by_p (CDI_POST_DOMINATORS, succ, bb);
+
+ if (wlims.always_executed)
+ {
+ edge_iterator ei;
+ edge e, found = NULL, found_back = NULL;
+ /* Look for a fallthru and possibly a single backedge. */
+ FOR_EACH_EDGE (e, ei, bb->preds)
+ {
+ /* Ignore backedges. */
+ if (dominated_by_p (CDI_DOMINATORS, e->src, bb))
+ {
+ if (found_back)
+ {
+ found = NULL;
+ break;
+ }
+ found_back = e;
+ continue;
+ }
+ if (found)
+ {
+ found = NULL;
+ break;
+ }
+ found = e;
+ }
+ if (found)
+ for (gphi_iterator si = gsi_start_phis (bb); !gsi_end_p (si);
+ gsi_next (&si))
+ {
+ gphi *phi = si.phi ();
+ tree def = PHI_ARG_DEF_FROM_EDGE (phi, found);
+ if (TREE_CODE (def) != SSA_NAME
+ || !SSA_NAME_IS_DEFAULT_DEF (def)
+ || virtual_operand_p (def))
+ continue;
+ /* If there's a default def on the fallthru edge PHI
+ value and there's a use that post-dominates entry
+ then that use is uninitialized and we can warn. */
+ imm_use_iterator iter;
+ use_operand_p use_p;
+ gimple *use_stmt = NULL;
+ FOR_EACH_IMM_USE_FAST (use_p, iter, gimple_phi_result (phi))
+ {
+ use_stmt = USE_STMT (use_p);
+ if (gimple_location (use_stmt) != UNKNOWN_LOCATION
+ && dominated_by_p (CDI_POST_DOMINATORS, succ,
+ gimple_bb (use_stmt))
+ /* If we found a non-fallthru edge make sure the
+ use is inside the loop, otherwise the backedge
+ can serve as initialization. */
+ && (!found_back
+ || dominated_by_p (CDI_DOMINATORS, found_back->src,
+ gimple_bb (use_stmt))))
+ break;
+ use_stmt = NULL;
+ }
+ if (use_stmt)
+ warn_uninit (OPT_Wuninitialized, def, SSA_NAME_VAR (def),
+ SSA_NAME_VAR (def),
+ "%qD is used uninitialized", use_stmt,
+ UNKNOWN_LOCATION);
+ }
+ }
+
for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
{
gimple *stmt = gsi_stmt (gsi);
@@ -3135,6 +3200,7 @@ execute_early_warn_uninitialized (void)
optimization we want to warn about possible uninitialized as late
as possible, thus don't do it here. However, without
optimization we need to warn here about "may be uninitialized". */
+ calculate_dominance_info (CDI_DOMINATORS);
calculate_dominance_info (CDI_POST_DOMINATORS);
warn_uninitialized_vars (/*warn_maybe_uninitialized=*/!optimize);
--
2.26.2
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