imcc: error on exceptions in constant folding

When an op with only constants args throws an exception like div by zero,
eval just returns the address of the handler, not the handler.  So we only
know that something is wrong, not what.

The exception message should be improved later.  For now just error with
eval_ins: unhandled exception for op '%s'

Fixes #1236

compilers/imcc/optimizer.c

@@ -927,7 +927,7 @@ eval_ins(ARGMOD(imc_info_t *imcc), ARGIN(const char *op), size_t ops,
             break;
           default:
             IMCC_fatal(imcc, 1, "eval_ins"
-                    "invalid arg #%d for op '%s' not found\n",
+                    ": invalid arg #%d for op '%s' not found\n",
                     i, op);
         }
     }
@@ -940,10 +940,16 @@ eval_ins(ARGMOD(imc_info_t *imcc), ARGIN(const char *op), size_t ops,
     pc = (OP_INFO_OPFUNC(op_info)) (eval, imcc->interp);
     Parrot_runloop_free_jump_point(imcc->interp);
     /* the returned pc is either incremented by op_count or is eval,
-     * as the branch offset is 0 - return true if it branched
+     * as the branch offset is 0 - return true if it branched.
+     * or if the op threw an exception (e.g. DIV_BY_ZERO), the pc of the handler.
      */
-    PARROT_ASSERT(pc == eval + op_info->op_count || pc == eval);
-    return pc == eval;
+    if (pc == eval)
+        return -1;
+    else if (pc == eval + op_info->op_count)
+        return 0;
+    else /* Todo: just follow the exception address */
+        IMCC_fatal(imcc, 1, "eval_ins"
+                   ": fatal exception in op '%s'\n", op);
 }
 
 /*

src/string/namealias.c

@@ -1,5 +1,5 @@
-/* ANSI-C code produced by gperf version 3.0.4 */
-/* Command-line: gperf --output-file=tmp_namealias.c src/string/namealias_c.in  */
+/* ANSI-C code produced by gperf version 3.1 */
+/* Command-line: gperf --output-file=tmp_namealias.c src/string/namealias_c.in */
 /* Computed positions: -k'1,14,$' */
 
 #if !((' ' == 32) && ('!' == 33) && ('"' == 34) && ('#' == 35) \

t/compilers/imcc/syn/const.t

@@ -1,5 +1,5 @@
 #!perl
-# Copyright (C) 2001-2014, Parrot Foundation.
+# Copyright (C) 2001-2017, Parrot Foundation.
 
 use strict;
 use warnings;
@@ -8,7 +8,7 @@ use vars qw($TODO);
 
 use Test::More;
 use Parrot::Config;
-use Parrot::Test tests => 40;
+use Parrot::Test tests => 41;
 
 pir_output_is( <<'CODE', <<'OUT', "globalconst 1" );
 .sub 'main' :main
@@ -668,6 +668,15 @@ OUT
 #/Method 'new' not found for non-object/
 #OUT
 
+# TODO: This really should just exit with Divide by zero, as parrot_old did
+pir_error_output_like( <<'CODE', <<'OUT', 'Exceptions in the constant folder [GH #1236]')
+.sub a
+  $N0=0//0
+.end
+CODE
+/ exception in op 'fdiv_n_n_n'/
+OUT
+
 # Local Variables:
 #   mode: cperl
 #   cperl-indent-level: 4