From: Evan Cheng <evan.cheng@apple.com>
Date: Tue, 20 Mar 2007 22:22:38 +0000 (+0000)
Subject: Potential spiller improvement.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=c3c70881cf7457535182add96d0ea96a3a12e9f2;p=oota-llvm.git

Potential spiller improvement.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35228 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/README.txt b/lib/CodeGen/README.txt
new file mode 100644
index 00000000000..3f295126fb3
--- /dev/null
+++ b/lib/CodeGen/README.txt
@@ -0,0 +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.