[pushed] analyzer: fixes to side-effects for built-in functions [PR107565]
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Commit Message
Previously, if the analyzer saw a call to a non-pure and non-const
built-in function that it didn't have explicit knowledge of the behavior
of, it would fall back to assuming that the builtin could have arbitrary
behavior, similar to a function defined outside of the current TU.
However, this only worked for BUILTIN_NORMAL functions that matched
gimple_builtin_call_types_compatible_p; for BUILT_IN_FRONTEND and
BUILT_IN_MD, and for mismatched types the analyzer would erroneously
assume that the builtin had no side-effects, leading e.g. to
PR analyzer/107565, where the analyzer falsely reported that x
was still uninitialized after this target-specific builtin:
_1 = __builtin_ia32_rdrand64_step (&x);
This patch generalizes the handling to cover all classes of builtin,
fixing the above false positive.
Unfortunately this patch regresses gcc.dg/analyzer/pr99716-1.c due to
the:
fprintf (fp, "hello");
being optimized to:
__builtin_fwrite ("hello", 1, (ssizetype)5, fp_6);
and the latter has gimple_builtin_call_types_compatible_p return false,
whereas the original call had it return true. I'm assuming that this is
an optimization bug, and have filed it as PR middle-end/108988. The
effect on the analyzer is that it fails to recognize the call to
__builtin_fwrite and instead assumes arbitraty side-effects (including
that it could call fclose on fp, hence the report about the leak goes
away).
I tried various more involved fixes with new heuristics for handling
built-ins that aren't explicitly covered by the analyzer, but those
fixes tended to introduce many more regressions, so I'm going with this
simpler fix.
Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.
Integration testing shows no change in results.
Pushed to trunk as r13-6398-g24ebc5404b88b7.
gcc/analyzer/ChangeLog:
PR analyzer/107565
* region-model.cc (region_model::on_call_pre): Flatten logic by
returning early. Consolidate logic for detecting const and pure
functions. When considering whether an unhandled built-in
function has side-effects, consider all kinds of builtin, rather
than just BUILT_IN_NORMAL, and don't require
gimple_builtin_call_types_compatible_p.
gcc/testsuite/ChangeLog:
PR analyzer/107565
* gcc.dg/analyzer/builtins-pr107565.c: New test.
* gcc.dg/analyzer/pr99716-1.c (test_2): Mark the leak as xfailing.
Signed-off-by: David Malcolm <dmalcolm@redhat.com>
---
gcc/analyzer/region-model.cc | 44 ++++++++-----------
.../gcc.dg/analyzer/builtins-pr107565.c | 29 ++++++++++++
gcc/testsuite/gcc.dg/analyzer/pr99716-1.c | 6 ++-
3 files changed, 53 insertions(+), 26 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/analyzer/builtins-pr107565.c
@@ -1477,8 +1477,6 @@ region_model::on_call_pre (const gcall *call, region_model_context *ctxt)
{
call_details cd (call, this, ctxt);
- bool unknown_side_effects = false;
-
/* Special-case for IFN_DEFERRED_INIT.
We want to report uninitialized variables with -fanalyzer (treating
-ftrivial-auto-var-init= as purely a mitigation feature).
@@ -1487,7 +1485,7 @@ region_model::on_call_pre (const gcall *call, region_model_context *ctxt)
view of the analyzer. */
if (gimple_call_internal_p (call)
&& gimple_call_internal_fn (call) == IFN_DEFERRED_INIT)
- return false;
+ return false; /* No side effects. */
/* Get svalues for all of the arguments at the callsite, to ensure that we
complain about any uninitialized arguments. This might lead to
@@ -1532,33 +1530,29 @@ region_model::on_call_pre (const gcall *call, region_model_context *ctxt)
= get_known_function (gimple_call_internal_fn (call)))
{
kf->impl_call_pre (cd);
- return false;
+ return false; /* No further side effects. */
}
- if (callee_fndecl)
- {
- int callee_fndecl_flags = flags_from_decl_or_type (callee_fndecl);
+ if (!callee_fndecl)
+ return true; /* Unknown side effects. */
- if (const known_function *kf = get_known_function (callee_fndecl, cd))
- {
- kf->impl_call_pre (cd);
- return false;
- }
- else if (fndecl_built_in_p (callee_fndecl, BUILT_IN_NORMAL)
- && gimple_builtin_call_types_compatible_p (call, callee_fndecl))
- {
- if (!(callee_fndecl_flags & (ECF_CONST | ECF_PURE)))
- unknown_side_effects = true;
- }
- else if (!fndecl_has_gimple_body_p (callee_fndecl)
- && (!(callee_fndecl_flags & (ECF_CONST | ECF_PURE)))
- && !fndecl_built_in_p (callee_fndecl))
- unknown_side_effects = true;
+ if (const known_function *kf = get_known_function (callee_fndecl, cd))
+ {
+ kf->impl_call_pre (cd);
+ return false; /* No further side effects. */
}
- else
- unknown_side_effects = true;
- return unknown_side_effects;
+ const int callee_fndecl_flags = flags_from_decl_or_type (callee_fndecl);
+ if (callee_fndecl_flags & (ECF_CONST | ECF_PURE))
+ return false; /* No side effects. */
+
+ if (fndecl_built_in_p (callee_fndecl))
+ return true; /* Unknown side effects. */
+
+ if (!fndecl_has_gimple_body_p (callee_fndecl))
+ return true; /* Unknown side effects. */
+
+ return false; /* No side effects. */
}
/* Update this model for the CALL stmt, using CTXT to report any
new file mode 100644
@@ -0,0 +1,29 @@
+/* { dg-do compile { target { x86_64-*-* && lp64 } } } */
+/* { dg-additional-options "-mrdrnd" } */
+
+unsigned short
+hardware_rand16 (void)
+{
+ unsigned short x;
+ while (! __builtin_ia32_rdrand16_step (&x))
+ continue;
+ return x; /* { dg-bogus "uninit" } */
+}
+
+unsigned int
+hardware_rand32 (void)
+{
+ unsigned int x;
+ while (! __builtin_ia32_rdrand32_step (&x))
+ continue;
+ return x; /* { dg-bogus "uninit" } */
+}
+
+unsigned long long
+hardware_rand64 (void)
+{
+ unsigned long long int x;
+ while (! __builtin_ia32_rdrand64_step (&x))
+ continue;
+ return x; /* { dg-bogus "uninit" } */
+}
@@ -27,7 +27,11 @@ test_2 (void)
FILE *fp = fopen ("/tmp/test", "w");
fprintf (fp, "hello");
}
-} /* { dg-warning "leak of FILE 'fp'" } */
+} /* { dg-warning "leak of FILE 'fp'" "" { xfail *-*-* } } */
+/* TODO: fails on some targets due to fprintf call being optimized to
+ __builtin_fwrite with a size argument (idx 2) that fails
+ gimple_builtin_call_types_compatible_p, and thus the known_function
+ for __builtin_fwrite not being used (PR middle-end/108988). */
FILE *fp3;