[m-rev.] diff: fix bug #204

[Peter Wang]

Branches: main

Fix bug #204.  Deconstruct of packed arguments was broken due to a mistake in
the RTTI tables.

compiler/prog_data.m:
compiler/rtti_out.m:
compiler/rtti_to_mlds.m:
	Correct the computation of the number of bits occupied by a packed
	argument, given the bit-mask.

tests/hard_coded/Mmakefile:
tests/hard_coded/zinc_pack_bug.exp:
tests/hard_coded/zinc_pack_bug.m:
	Add test case.

diff --git a/compiler/prog_data.m b/compiler/prog_data.m
index 07f4702..424d0fd 100644
--- a/compiler/prog_data.m
+++ b/compiler/prog_data.m
@@ -1707,7 +1707,7 @@ equivalent_cons_ids(ConsIdA, ConsIdB) :-
     % two or more arguments which share the same word. The argument occupies
     % the lowest bits in the word so no shifting is required. The other
     % arguments can be masked out with the bit-mask `Mask'. The actual number
-    % of bits occupied by the argument is `int.log2(Mask)'.
+    % of bits occupied by the argument is `int.log2(Mask + 1)'.
     %
     % `partial_word_shifted(Shift, Mask)' indicates that the argument is one of
     % the subsequent arguments which share the same word. `Shift' is the
diff --git a/compiler/rtti_out.m b/compiler/rtti_out.m
index a88a77e..e70ed32 100644
--- a/compiler/rtti_out.m
+++ b/compiler/rtti_out.m
@@ -1167,11 +1167,11 @@ output_du_arg_locns_2([ArgInfo | ArgInfos], PrevSlotNum, !IO) :-
     ;
         ArgWidth = partial_word_first(Mask),
         Shift = 0,
-        int.log2(Mask, Bits),
+        int.log2(Mask + 1, Bits),
         SlotNum = PrevSlotNum + 1
     ;
         ArgWidth = partial_word_shifted(Shift, Mask),
-        int.log2(Mask, Bits),
+        int.log2(Mask + 1, Bits),
         SlotNum = PrevSlotNum
     ),
     io.format("\t{ %d, %d, %d },\n", [i(SlotNum), i(Shift), i(Bits)], !IO),
diff --git a/compiler/rtti_to_mlds.m b/compiler/rtti_to_mlds.m
index 074ac16..dd28f46 100644
--- a/compiler/rtti_to_mlds.m
+++ b/compiler/rtti_to_mlds.m
@@ -999,10 +999,10 @@ gen_field_locn(RttiId, ArgInfo, ArgLocnInitializer, !Offset) :-
         ArgWidth = partial_word_first(Mask),
         !:Offset = !.Offset + 1,
         Shift = 0,
-        int.log2(Mask, Bits)
+        int.log2(Mask + 1, Bits)
     ;
         ArgWidth = partial_word_shifted(Shift, Mask),
-        int.log2(Mask, Bits)
+        int.log2(Mask + 1, Bits)
     ),
     ArgLocnInitializer = init_struct(mlds_rtti_type(item_type(RttiId)), [
         gen_init_int(!.Offset),
diff --git a/tests/hard_coded/Mmakefile b/tests/hard_coded/Mmakefile
index 0a9189b..2819c4e 100644
--- a/tests/hard_coded/Mmakefile
+++ b/tests/hard_coded/Mmakefile
@@ -318,7 +318,8 @@ ORDINARY_PROGS=	\
 	write_reg1 \
 	write_reg2 \
 	write_xml \
-	xmlable_test
+	xmlable_test \
+	zinc_pack_bug
 
 # --transitive-intermodule-optimization is incompatible with mmc --make.
 ifneq ($(MMAKE_USE_MMC_MAKE),yes)
diff --git a/tests/hard_coded/zinc_pack_bug.exp b/tests/hard_coded/zinc_pack_bug.exp
new file mode 100644
index 0000000..1a9a2e6
--- /dev/null
+++ b/tests/hard_coded/zinc_pack_bug.exp
@@ -0,0 +1 @@
+sym_variable(ti_par_int, undefined, global_var)
diff --git a/tests/hard_coded/zinc_pack_bug.m b/tests/hard_coded/zinc_pack_bug.m
new file mode 100644
index 0000000..a000058
--- /dev/null
+++ b/tests/hard_coded/zinc_pack_bug.m
@@ -0,0 +1,43 @@
+% vim: ft=mercury ts=4 sw=4 et wm=0 tw=0
+
+% rotd-2011-07-09 generates code that seg. faults when executed.
+
+:- module zinc_pack_bug.
+:- interface.
+
+:- import_module io.
+
+:- pred main(io::di, io::uo) is det.
+
+:- implementation.
+
+:- type type_inst
+    --->    ti_par_bottom
+    ;       ti_par_int
+    ;       ti_var_int
+    ;       ti_unknown
+    .
+:- type symbol
+    --->    sym_variable(
+                type_inst        :: type_inst,
+                is_defined       :: is_defined,
+                variable_kind    :: variable_kind
+            ).
+
+:- type is_defined
+    --->    defined
+    ;       undefined.
+
+:- type variable_kind
+    --->    global_var
+    ;       type_constraint_var
+    ;       let_var
+    ;       generator_var
+    ;       pred_arg
+    ;       func_arg
+    ;       ann_arg.
+
+main(!IO) :-
+    NewSym = sym_variable(ti_par_int, undefined, global_var),
+    io.write(NewSym, !IO),
+    io.nl(!IO).

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