Author: lattner
Date: Sat Jan 26 14:12:07 2008
New Revision: 46405
URL: http://llvm.org/viewvc/llvm-project?rev=46405&view=rev
Log:
Add some notes.
Modified:
llvm/trunk/lib/Target/X86/README-SSE.txt
Modified: llvm/trunk/lib/Target/X86/README-SSE.txt
URL:
http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/README-SSE.txt?rev=46405&r1=46404&r2=46405&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/README-SSE.txt (original)
+++ llvm/trunk/lib/Target/X86/README-SSE.txt Sat Jan 26 14:12:07 2008
@@ -704,3 +704,21 @@
We should use movmskp{s|d} instead.
+//===---------------------------------------------------------------------===//
+
+CodeGen/X86/vec_align.ll tests whether we can turn 4 scalar loads into a single
+(aligned) vector load. This functionality has a couple of problems.
+
+1. The code to infer alignment from loads of globals is in the X86 backend,
+ not the dag combiner. This is because dagcombine2 needs to be able to see
+ through the X86ISD::Wrapper node, which DAGCombine can't really do.
+2. The code for turning 4 x load into a single vector load is target
+ independent and should be moved to the dag combiner.
+3. The code for turning 4 x load into a vector load can only handle a direct
+ load from a global or a direct load from the stack. It should be
generalized
+ to handle any load from P, P+4, P+8, P+12, where P can be anything.
+4. The alignment inference code cannot handle loads from globals in non-static
+ mode because it doesn't look through the extra dyld stub load. If you try
+ vec_align.ll without -relocation-model=static, you'll see what I mean.
+
+//===---------------------------------------------------------------------===//
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