analyzer: fixes to side-effects for built-in functions [PR107565]

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.

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

@@ -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)
+  if (!callee_fndecl)
+    return true; /* Unknown side effects.  */
+
+  if (const known_function *kf = get_known_function (callee_fndecl, cd))
     {
-      int callee_fndecl_flags = flags_from_decl_or_type (callee_fndecl);
-
-      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;
+      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

gcc/testsuite/gcc.dg/analyzer/builtins-pr107565.c

@@ -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" } */
+}

gcc/testsuite/gcc.dg/analyzer/pr99716-1.c

@@ -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;