[llvm-commits] CVS: llvm/lib/Target/X86/README.txt

[Chris Lattner]

Changes in directory llvm/lib/Target/X86:

README.txt updated: 1.141 -> 1.142
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Log message:

add a note


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Diffs of the changes:  (+27 -0)

 README.txt |   27 +++++++++++++++++++++++++++
 1 files changed, 27 insertions(+)


Index: llvm/lib/Target/X86/README.txt
diff -u llvm/lib/Target/X86/README.txt:1.141 llvm/lib/Target/X86/README.txt:1.142
--- llvm/lib/Target/X86/README.txt:1.141	Fri Oct  6 12:39:34 2006
+++ llvm/lib/Target/X86/README.txt	Thu Oct 12 17:01:26 2006
@@ -734,3 +734,30 @@
         ret
 
 //===---------------------------------------------------------------------===//
+
+Consider the expansion of:
+
+uint %test3(uint %X) {
+        %tmp1 = rem uint %X, 255
+        ret uint %tmp1
+}
+
+Currently it compiles to:
+
+...
+        movl $2155905153, %ecx
+        movl 8(%esp), %esi
+        movl %esi, %eax
+        mull %ecx
+...
+
+This could be "reassociated" into:
+
+        movl $2155905153, %eax
+        movl 8(%esp), %ecx
+        mull %ecx
+
+to avoid the copy.  In fact, the existing two-address stuff would do this
+except that mul isn't a commutative 2-addr instruction.  I guess this has
+to be done at isel time based on the #uses to mul?
+