[Mono-bugs] [Bug 60697][Wis] New - Optimize cgt / ldc.i4.0 / ceq type sequences

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Changed by bmaurer@users.sf.net.

http://bugzilla.ximian.com/show_bug.cgi?id=60697

--- shadow/60697	2004-06-24 11:49:53.000000000 -0400
+++ shadow/60697.tmp.28016	2004-06-24 11:49:53.000000000 -0400
@@ -0,0 +1,50 @@
+Bug#: 60697
+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: Optimize cgt / ldc.i4.0 / ceq type sequences
+
+The IL language does not contain all the possible comparisons that could be
+generated. For example, there is no compare-lt-or-eq. You have to generate
+cgt / ldc.i4.0 / ceq.
+
+But the operations to do this do exist in assembly (at least for the x86),
+but we do not use them. Consider the following code:
+
+class T {
+	static void Main () { B (); }
+	
+	static bool B ()
+	{
+		int i = 0;
+		int j = 1;
+		
+		return i <= j;	
+	}
+}
+
+We generate:
+
+   f:	bf 00 00 00 00       	mov    edi,0x0
+  14:	be 01 00 00 00       	mov    esi,0x1
+  19:	8b c6                	mov    eax,esi
+  1b:	3b f8                	cmp    edi,eax
+  1d:	0f 9f c0             	setg   al
+  20:	0f b6 c0             	movzx  eax,al
+  23:	85 c0                	test   eax,eax
+  25:	0f 94 c0             	sete   al
+  28:	0f b6 c0             	movzx  eax,al
+
+Clearly, we could optimize this down to one cmp operation.