[Mono-bugs] [Bug 61894][Wis] New - [PATCH] add a simplistic deadce engine to copyprop

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Changed by bmaurer@users.sf.net.

http://bugzilla.ximian.com/show_bug.cgi?id=61894

--- shadow/61894	2004-07-23 19:51:33.000000000 -0400
+++ shadow/61894.tmp.32299	2004-07-23 19:51:33.000000000 -0400
@@ -0,0 +1,35 @@
+Bug#: 61894
+Product: Mono: Runtime
+Version: unspecified
+OS: 
+OS Details: 
+Status: NEW   
+Resolution: 
+Severity: 
+Priority: Wishlist
+Component: misc
+AssignedTo: mono-bugs@ximian.com                            
+ReportedBy: bmaurer@users.sf.net               
+QAContact: mono-bugs@ximian.com
+TargetMilestone: ---
+URL: 
+Cc: 
+Summary: [PATCH] add a simplistic deadce engine to copyprop
+
+Copy propagation is extremely likely to create dead variables. Right now,
+these variables stay around in the source code unless the -O=deadce
+optimization is enabled. However, this optimization requires the building
+of the SSA form, which is expensive -- especially in JIT mode.
+
+This patch implements an extremely simple version of deadce. Basically, any
+variable without reads will be eliminated.
+
+This extra pass through the IR does not cause an increase in compile time.
+In fact, it has the benefit of reducing the work that must be done by the
+SSA pass -- running -O=deadce,copyprop now is faster than it was before
+(nb: it is still slower [in jit time] than -O=deadce, this is because SCCP
+is enabled with -O=copyprop -- this should be fixed)
+
+In the patch, I had to remove the duplicated calls to cfolding. What
+happened was that some trees got their operands swapped -- so one of the
+arms was never visited. This resulted in some errors.