Put the comment about the contents of stack slots before the initial

code_gen.pp:
	Put the comment about the contents of stack slots before the initial
	label, since this way it will be preserved by optimizations.

cse_detection.m:
	Extended the search to look for cses in if-then-elses and switches
	as well as disjunctions. Removed InstmapDelta from preds in which it
	was not being used.

det_analysis.m:
	Make the diagnosis routines more robust. The changes here avoid the
	Philip's problems with lexical.m.

jumpopt.m:
	Minor formatting changes.

livemap.m:
	Avoid duplicating livevals instructions when optimizations are
	repeated, since this can confuse some optimizations.

llds.m:
	Minor documentation change.

make_hlds.m:
	Minor formatting change.

mercury_compile.pp:
	Do not map arguments to registers if any semantic errors have been
	found.

middle_rec.m and code_aux.m:
	Apply middle recursion only if tail recursion is not possible,
	since tail recursion yields more efficient code.

opt_util.m:
	Added a predicate to recognize constant conditions in if_vals.
	Modified a predicate to make it better suited for frameopt.

optimize.pp:
	Changed the way optimizations were repeated to allow better control.
	Repeat peephole once more after frameopt, since the new frameopt
	can benefit from this.

options.m:
	Removed the --compile-to-c option, which was obsolete. Added an
	option for predicate-wide value numbering, which is off by default.
	Changed some of the default values of optimization flags to reduce
	compilation time while holding the loss of speed of generated code
	to a minimum.

peephole.m:
	Look for if_vals whose conditions are constants, and eliminate the
	if_val or turn it into a goto depending on the value of the constant.
	Generalized the condition for optimizing incr_sp/decr_sp pairs.

value_number.m:
	Added a prepass to separate primary tag tests in if-then-elses from
	the test of the secondary tag, which requires dereferencing the
	pointer.

	Added sanity check routines to test two aspects of the generated code.
	First, whether it produces the same values for the live variables as
	the original code, and second, whether it has moved any dereferences
	of a pointer before a test of the tag of that pointer. If either test
	fails, we use the old instruction sequence.

vn_debug.m:
	New messages to announce the failure of the sanity checks. They are
	enabled by default, but of course can only appear if value numbering
	is turned on (it is still off by default).

vn_flush.m:
	Threaded a list of forbidden lvals (lvals that may not be assigned to)
	through the flushing routines. When saving the old value of an lval
	that is being assigned to, we use this list to avoid modifying any of
	the values used on the right hand side of the assignment, even if the
	saving of an old value results in assignment that requires another
	save, and so on recursively.

	When the flushing of a node_lval referred to a shared vn, the uses of
	the access vns of the node_lvals were not being adjusted properly.
	Now they are.

vn_order.m:
	The ctrl_vn phase of the ordering was designed to ensure that all
	nodes that need not come before a control node come after it. However,
	nodes were created after this phase operated, causing leakage of some
	value nodes in front of control nodes. Some of these led to pointer
	dereferences before tag tests, causing bus errors. The ctrl_vn phase
	is now last to avoid this problem.

vn_table.m:
	Added an extra interface predicate to support the sanity checks in
	value_number.

vn_util.m:
	The transformation of c1-e2 into (0-e2)+c1 during vnrval simplification
	could lead to an infinite loop in the compiler if c1 was zero. A test
	for this case now prevents the loop.

compiler/code_gen.pp

@@ -487,8 +487,8 @@ code_gen__generate_det_prolog(EntryCode, SUsed) -->
 	{ code_util__make_local_entry_label(ModuleInfo, PredId, ProcId,
 		Entry) },
 	{ CodeA = node([
-		label(Entry) - "Procedure entry point",
-		comment(CallInfoComment) - ""
+		comment(CallInfoComment) - "",
+		label(Entry) - "Procedure entry point"
 	]) },
 	(
 		{ Used = yes }
@@ -588,8 +588,8 @@ code_gen__generate_semi_prolog(EntryCode, SUsed) -->
 	{ code_util__make_local_entry_label(ModuleInfo, PredId, ProcId,
 		Entry) },
 	{ CodeA = node([
-		label(Entry) - "Procedure entry point",
-		comment(CallInfoComment) - ""
+		comment(CallInfoComment) - "",
+		label(Entry) - "Procedure entry point"
 	]) },
 	(
 		{ Used = yes }
@@ -722,8 +722,8 @@ code_gen__generate_non_prolog(EntryCode, no) -->
 	{ code_util__make_local_entry_label(ModuleInfo, PredId, ProcId,
 		Entry) },
 	{ CodeA = node([
-		label(Entry) - "Procedure entry point",
-		comment(CallInfoComment) - ""
+		comment(CallInfoComment) - "",
+		label(Entry) - "Procedure entry point"
 	]) },
 		% The `name' argument to mkframe() is just for
 		% debugging purposes.  We construct it as "predname/arity".