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

[Evan Cheng]

Changes in directory llvm/lib/CodeGen:

README.txt added (r1.1)
---
Log message:

Potential spiller improvement.

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Diffs of the changes:  (+27 -0)

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


Index: llvm/lib/CodeGen/README.txt
diff -c /dev/null llvm/lib/CodeGen/README.txt:1.1
*** /dev/null	Tue Mar 20 17:22:48 2007
--- llvm/lib/CodeGen/README.txt	Tue Mar 20 17:22:38 2007
***************
*** 0 ****
--- 1,27 ----
+ Common register allocation / spilling problem:
+ 
+ 	mul lr, r4, lr
+ 	str lr, [sp, #+52]
+ 	ldr lr, [r1, #+32]
+ 	sxth r3, r3
+ 	ldr r4, [sp, #+52]
+ 	mla r4, r3, lr, r4
+ 
+ can be:
+ 
+ 	mul lr, r4, lr
+         mov r4, lr
+ 	str lr, [sp, #+52]
+ 	ldr lr, [r1, #+32]
+ 	sxth r3, r3
+ 	mla r4, r3, lr, r4
+ 
+ and then "merge" mul and mov:
+ 
+ 	mul r4, r4, lr
+ 	str lr, [sp, #+52]
+ 	ldr lr, [r1, #+32]
+ 	sxth r3, r3
+ 	mla r4, r3, lr, r4
+ 
+ It also increase the likelyhood the store may become dead.