Author: lattner
Date: Fri Aug 24 10:17:59 2007
New Revision: 41359
URL: http://llvm.org/viewvc/llvm-project?rev=41359&view=rev
Log:
add a note
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=41359&r1=41358&r2=41359&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/README-SSE.txt (original)
+++ llvm/trunk/lib/Target/X86/README-SSE.txt Fri Aug 24 10:17:59 2007
@@ -630,3 +630,17 @@
ret
//===---------------------------------------------------------------------===//
+
+We should materialize vecetor constants like "all ones" and "signbit" with
+code like:
+
+ cmpeqps xmm1, xmm1 ; xmm1 = all-ones
+
+and:
+ cmpeqps xmm1, xmm1 ; xmm1 = all-ones
+ psrlq xmm1, 31 ; xmm1 = all 100000000000...
+
+instead of using a load from the constant pool. The later is important for
+ABS/NEG/copysign etc.
+
+//===---------------------------------------------------------------------===//
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