[imcc] Fixed last remaining -O2 issue #1044 t/pmc/exception-old_19.pir

Stop constant propagation at yield or invokecc for possible
push_eh/pop_eh non-local effects. This can undo the set of the constant
value.

See t/pmc/exception-old_19.pir:
cont = test() contains a push_eh, and the subsequent pop_eh at cont() changes
the value of the constant redux from 0 back to 1. So constant propagation for
redux=0 cannot delete "if redux goto done" and the done branch.

ChangeLog

@@ -1,33 +1,40 @@
 2014-03-18    release 6.2.0
     - Core
-	+ Re-enable old immc flags for parrot and parrot_old, such as
-	  -On -a -v -y -E -dxx. [GH #1033]
-	+ Fixed imcc -O1. Special-case get_global for branch_cond_loop_swap,
-          which broke nci tests [GH #1037]
-	+ Fixed imcc for -O2 to allow used_once elimination only for
-	  purely functional ops without side-effects [GH #1036]
-	+ Fixed most imcc -O2 errors in constant propagation
-	  = leading to empty ins->op ptrs when deleting or skipping
-	  certain instruction [GH #1039],
-	  = a wrong logic leading to missed detecting writes
-          from get_results [GH #1041],
-	  = propagate only matching types in setters [GH #1042], and
-	  = empty ins->next in used_once deletion [GH #1044].
-	  Only 1 remaining -O2 test regression.
+        + Re-enable old immc flags for parrot and parrot_old, such as
+          -On -a -v -y -E -dxx. [GH #1033]
+
+        + Fixed imcc -O1 and -O2.
+
+          -O1 fixes:
+          = Special-case get_global for branch_cond_loop_swap, which broke nci
+            tests [GH #1037]
+
+          -O2 used_once fixes:
+          = Allow used_once elimination only for purely functional ops
+            without side-effects [GH #1036]
+          = Empty ins->next in deletion [GH #1042].
+
+          -O2 constant propagation fixes:
+          = Empty ins->op ptrs when deleting or skipping certain instruction
+            [GH #1039],
+          = Wrong logic leading to missed detecting writes from get_results
+            [GH #1041],
+          = Propagate only matching types in setters [GH #1042],
+          = Stop at yield or invokecc for possible push_eh/pop_eh non-local
+            effects [GH #1044]
     - Build
-	+ Set emacs buffer-read-only:t tags in generated files [GH #1034]
-	+ Provide coda for generated include/*.pasm files [GH #1032]
-	+ Fix parser for bison 3 [GH #1031]
+        + Set emacs buffer-read-only:t tags in generated files [GH #1034]
+        + Provide coda for generated include/*.pasm files [GH #1032]
+        + Fix parser for bison 3 [GH #1031]
     - Deprecations
-	+ Warn on deprecated usage of append_configure_log()
+        + Warn on deprecated usage of append_configure_log()
     - Documentation
-	+ Updated pod for parrot and tools/build/c2str.pl
+        + Updated pod for parrot and tools/build/c2str.pl
     - Tests
-	+ Added -O1 and -O2 to fulltest
-	+ Mark failing -O2 test
+        + Added -O1 and -O2 to fulltest
     - Community
-	+ Got accepted for GSOC. Got a candidate for "Improve performance
-	  of method signatures"
+        + Parrot has been accepted to Google Summer of Code 2014
+        + Got a candidate for "Improve performance of method signatures"
 
 2014-02-18    release 6.1.0
     - Build

compilers/imcc/optimizer.c

@@ -693,7 +693,8 @@ strength_reduce(ARGMOD(imc_info_t *imcc), ARGMOD(IMC_Unit *unit))
 =item C<static int constant_propagation(imc_info_t *imcc, IMC_Unit *unit)>
 
 Does conservative constant propagation.
-This code will not propagate constants past labels or saves,
+
+This code will not propagate constants past labels, invokecc, yield or saves,
 even though sometimes it may be safe.
 
 =cut
@@ -734,6 +735,10 @@ constant_propagation(ARGMOD(imc_info_t *imcc), ARGMOD(IMC_Unit *unit))
         if (found) {
             Instruction *ins2;
 
+            /* Propagate the constant into all subsequent ops in the same basic block.
+               But skip on the first write into this constant.
+               Also skip on invokecc or yield ops, as they can contain pop_eh and
+               undo the constant value. GH #1044 */
             IMCC_debug(imcc, DEBUG_OPT2, "propagating constant %s from ", c->name);
             IMCC_debug_ins(imcc, DEBUG_OPT2, ins);
             for (ins2 = ins->next; ins2; ins2 = ins2->next) {
@@ -745,6 +750,8 @@ constant_propagation(ARGMOD(imc_info_t *imcc), ARGMOD(IMC_Unit *unit))
                     IMCC_debug(imcc, DEBUG_OPT2, "\tchecking op ");
                     IMCC_debug_ins(imcc, DEBUG_OPT2, ins2);
                 }
+                if (ins2->type & ITPCCSUB || ins->type & ITPCCYIELD)
+                    goto next_constant;
                 /* was opsize - 2, changed to n_r - 1 */
                 for (i = ins2->symreg_count - 1; i >= 0; i--) {
                     if (STREQ(o->name, ins2->symregs[i]->name)) {

t/pmc/exception-old.t

@@ -431,16 +431,17 @@ something broke
 current inst/
 OUTPUT
 
-TODO: {
-    local $TODO = '-O2 t/pmc/exception-old_19.pir regression #1044'
-      if $ENV{TEST_PROG_ARGS} =~ / -O2/;
-    pir_output_is(<<'CODE', <<'OUTPUT', "taking a continuation promotes RetCs");
+pir_output_is(<<'CODE', <<'OUTPUT', "taking a continuation promotes RetCs");
 ## This test creates a continuation in a inner sub and re-invokes it later.  The
 ## re-invocation signals an error, which is caught by an intermediate sub.
 ## Returning from the "test" sub the second time failed in r28794; invoking
 ## parrot with "-D80" shows clearly that the "test" context was being recycled
 ## prematurely.  For some reason, it is necessary to signal the error in order
 ## to expose the bug.
+## See also -O2 t/pmc/exception-old_19.pir regression [GH #1044]
+## cont = test() contains a push_eh, and the subsequent pop_eh at cont() changes
+## the value of the constant redux from 0 back to 1. So constant propagation for
+## redux=0 cannot delete "if redux goto done" and the done branch.
 .sub main :main
     .local int redux
     .local pmc cont
@@ -495,7 +496,6 @@ calling cont
 back from test
 done.
 OUTPUT
-}
 
 pir_error_output_like( <<'CODE', <<'OUTPUT', "throw - no handler" );
 .sub main :main