[m-rev.] diff: detism `failure' does not imply tail call

[Fergus Henderson]

On 31-Jan-2002, Fergus Henderson <fjh at cs.mu.OZ.AU> wrote:
> Fix a bug where we weren't getting proper tail recursion optimization in
> the MLDS->C back-end for procedures with output arguments and determinism
> `erroneous'.
> 
> compiler/ml_call_gen.m:
> 	Mark calls with determinism `erroneous' or `failure' as tail calls.

Estimated hours taken: 0.5
Branches: main

Fix a bug that broke tests/hard_coded/unused_float_box_test.m
in MLDS grades at -O4 and higher.

compiler/ml_call_gen.m:
compiler/ml_tailcall.m:
	Don't mark procedures with determinism `failure' as tail calls --
	that's not always correct.  The called procedured can fail,
	i.e. return FALSE to the caller, and then the caller can continue
	to do other computations.

Workspace: /home/earth/fjh/ws-earth4/mercury
Index: compiler/ml_call_gen.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/ml_call_gen.m,v
retrieving revision 1.29
diff -u -d -r1.29 ml_call_gen.m
--- compiler/ml_call_gen.m	1 Feb 2002 22:09:07 -0000	1.29
+++ compiler/ml_call_gen.m	6 Feb 2002 18:40:35 -0000
@@ -447,10 +447,9 @@
 	%
 	% build the MLDS call statement
 	%
-	% if the called procedure has determinism `erroneous' or `failure',
+	% if the called procedure has determinism `erroneous'
 	% then it's always safe to make this call a tail call.
-	{ determinism_components(Detism, _, NumSolns) },
-	{ NumSolns = at_most_zero ->
+	{ Detism = erroneous ->
 		CallOrTailcall = tail_call
 	;
 		CallOrTailcall = call
Index: compiler/ml_tailcall.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/ml_tailcall.m,v
retrieving revision 1.13
diff -u -d -r1.13 ml_tailcall.m
--- compiler/ml_tailcall.m	1 Feb 2002 22:09:08 -0000	1.13
+++ compiler/ml_tailcall.m	6 Feb 2002 18:36:01 -0000
@@ -45,7 +45,7 @@
 % any backend support for them.
 %
 % Note that ml_call_gen.m will also mark calls to procedures with determinism
-% `erroneous' or `failure' as tail calls when it generates them.
+% `erroneous' as tail calls when it generates them.
 
 %-----------------------------------------------------------------------------%
 

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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