tree-optimization/118521 - bogus diagnostic from unreachable code

When SCCP does final value replacement we end up with unfolded IL like

__result_274 = _150 + 1;
...
__new_finish_106 = __result_274 + 3;  <-- from SCCP
_115 = _150 + 4;
if (__new_finish_106 != _115)

this does only get rectified by the next full folding which happens
in forwprop4 which is after the strlen pass emitting the unwanted
diagnostic.  The following mitigates this case in a similar way as
r15-7472 did for PR118817 - by ensuring we have the IL folded.
This is done by simply folding all immediate uses of the former
PHI def that SCCP replaces.  All other more general approaches have
too much fallout at this point.

	PR tree-optimization/118521
	* tree-scalar-evolution.cc (final_value_replacement_loop):
	Fold uses of the replaced PHI def.

	* g++.dg/torture/pr118521.C: New testcase.

diff --git a/gcc/testsuite/g++.dg/torture/pr118521.C b/gcc/testsuite/g++.dg/torture/pr118521.C
new file mode 100644 (file)
index 0000000..1a66aca
--- /dev/null
+++ b/gcc/testsuite/g++.dg/torture/pr118521.C
@@ -0,0 +1,14 @@
+// { dg-do compile }
+// { dg-additional-options "-Wall" }
+
+#include <vector> // dg-bogus new_allocator.h:191 warning: writing 1 byte into a region of size 0
+
+void bar(std::vector<char>);
+
+void foo()
+{
+  std::vector<char> v{1, 2};
+  v.insert(v.end(), 2, 0);
+  v.push_back(1);
+  bar(v);
+}

diff --git a/gcc/tree-scalar-evolution.cc b/gcc/tree-scalar-evolution.cc
index 0ba85917d410b045ba8401f3d446bd42b5965171..4ca08751a0d3dcdc6d7dae730e3a56cebfd93581 100644 (file)
--- a/gcc/tree-scalar-evolution.cc
+++ b/gcc/tree-scalar-evolution.cc
@@ -284,6 +284,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-into-ssa.h"
 #include "builtins.h"
 #include "case-cfn-macros.h"
+#include "tree-eh.h"
 
 static tree analyze_scalar_evolution_1 (class loop *, tree);
 static tree analyze_scalar_evolution_for_address_of (class loop *loop,
@@ -3947,6 +3948,23 @@ final_value_replacement_loop (class loop *loop)
          print_gimple_stmt (dump_file, SSA_NAME_DEF_STMT (rslt), 0);
          fprintf (dump_file, "\n");
        }
+
+      /* Re-fold immediate uses of the replaced def, but avoid
+        CFG manipulations from this function.  For now only do
+        a single-level re-folding, not re-folding uses of
+        folded uses.  */
+      if (! SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rslt))
+       {
+         gimple *use_stmt;
+         imm_use_iterator imm_iter;
+         FOR_EACH_IMM_USE_STMT (use_stmt, imm_iter, rslt)
+           {
+             gimple_stmt_iterator gsi = gsi_for_stmt (use_stmt);
+             if (!stmt_can_throw_internal (cfun, use_stmt)
+                 && fold_stmt (&gsi, follow_all_ssa_edges))
+               update_stmt (gsi_stmt (gsi));
+           }
+       }
     }
 
   return any;