(vmprof)[brick:~/src/pypy] $ hg diff
obsolete feature not enabled but 157 markers found!
diff --git a/rpython/translator/backendopt/canraise.py b/rpython/translator/backendopt/canraise.py
--- a/rpython/translator/backendopt/canraise.py
+++ b/rpython/translator/backendopt/canraise.py
@@ -1,4 +1,6 @@
 from rpython.rtyper.lltypesystem.lloperation import LL_OPERATIONS
+from rpython.rtyper.lltypesystem import lltype
+from rpython.rtyper import rclass
 from rpython.tool.ansi_print import AnsiLogger
 from rpython.translator.backendopt import graphanalyze
 
@@ -8,6 +10,14 @@
 class RaiseAnalyzer(graphanalyze.BoolGraphAnalyzer):
     ignore_exact_class = None
 
+    def __init__(self, translator):
+        graphanalyze.BoolGraphAnalyzer.__init__(self, translator)
+        ed = translator.rtyper.exceptiondata
+        self.ll_assert_error = ed.get_standard_ll_exc_instance_by_class(
+            AssertionError)
+        self.ll_not_impl_error = ed.get_standard_ll_exc_instance_by_class(
+            NotImplementedError)
+
     def do_ignore_memory_error(self):
         self.ignore_exact_class = MemoryError
 
@@ -38,7 +48,22 @@
                         # it doesn't count.  We'll see the place that really
                         # raises the exception in the first place.
                         return False
-        return True
+        # find all the blocks leading to the raise block
+        blocks = []
+        for candidate in graph.iterblocks():
+            if len(candidate.exits) != 1:
+                continue
+            if candidate.exits[0].target is block:
+                blocks.append(candidate)
+        ignored = 0
+        for preblock in blocks:
+            assert len(preblock.operations) == 4
+            op = preblock.operations[0]
+            assert op.opname == 'same_as'
+            p = lltype.cast_pointer(rclass.OBJECTPTR, op.args[0].value)
+            if p == self.ll_assert_error or p == self.ll_not_impl_error:
+                ignored += 1
+        return ignored < len(blocks)
 
     # backward compatible interface
     def can_raise(self, op, seen=None):
diff --git a/rpython/translator/backendopt/test/test_canraise.py b/rpython/translator/backendopt/test/test_canraise.py
--- a/rpython/translator/backendopt/test/test_canraise.py
+++ b/rpython/translator/backendopt/test/test_canraise.py
@@ -1,7 +1,8 @@
+from rpython.conftest import option
+from rpython.rtyper.lltypesystem import rffi
 from rpython.translator.translator import TranslationContext, graphof
 from rpython.translator.backendopt.canraise import RaiseAnalyzer
 from rpython.translator.backendopt.all import backend_optimizations
-from rpython.conftest import option
 
 class TestCanRaise(object):
     def translate(self, func, sig):
@@ -253,3 +254,13 @@
         ra.do_ignore_memory_error()     # but it's potentially a KeyError
         result = ra.analyze_direct_call(graphof(t, h))
         assert result
+
+    def test_charp2str(self):
+        def f(a):
+            return len(rffi.charp2str(a))
+
+        t, ra = self.translate(f, [rffi.CCHARP])
+        ra.do_ignore_memory_error()
+        result = ra.analyze_direct_call(graphof(t, f))
+        assert not result # ignore AssertionError
+