[llvm-commits] [llvm] r39998 - /llvm/trunk/lib/Target/X86/README.txt

[Evan Cheng]

Author: evancheng
Date: Wed Jul 18 03:21:49 2007
New Revision: 39998

URL: http://llvm.org/viewvc/llvm-project?rev=39998&view=rev
Log:
New entry.

Modified:
    llvm/trunk/lib/Target/X86/README.txt

Modified: llvm/trunk/lib/Target/X86/README.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/README.txt?rev=39998&r1=39997&r2=39998&view=diff

==============================================================================
--- llvm/trunk/lib/Target/X86/README.txt (original)
+++ llvm/trunk/lib/Target/X86/README.txt Wed Jul 18 03:21:49 2007
@@ -1131,3 +1131,20 @@
         subl 4(%esp), %eax
         ret
 
+//===---------------------------------------------------------------------===//
+
+For code like:
+phi (undef, x)
+
+We get an implicit def on the undef side. If the phi is spilled, we then get:
+implicitdef xmm1
+store xmm1 -> stack
+
+It should be possible to teach the x86 backend to "fold" the store into the
+implicitdef, which just deletes the implicit def.
+
+These instructions should go away:
+#IMPLICIT_DEF %xmm1 
+movaps %xmm1, 192(%esp) 
+movaps %xmm1, 224(%esp) 
+movaps %xmm1, 176(%esp)