From: Chris Lattner <sabre@nondot.org>
Date: Tue, 13 May 2008 18:48:54 +0000 (+0000)
Subject: add a note
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=7171c836a93024d523b457b5a98782fa7ad5c97b;p=oota-llvm.git

add a note


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51060 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/X86/README-SSE.txt b/lib/Target/X86/README-SSE.txt
index 5c681e06e0c..5f114a855f0 100644
--- a/lib/Target/X86/README-SSE.txt
+++ b/lib/Target/X86/README-SSE.txt
@@ -764,4 +764,28 @@ madd:
 
 //===---------------------------------------------------------------------===//
 
+Consider:
+#include <emmintrin.h> 
+__m128 foo2 (float x) {
+ return _mm_set_ps (0, 0, x, 0);
+}
+
+In x86-32 mode, we generate this spiffy code:
+
+_foo2:
+	movss	4(%esp), %xmm0
+	pshufd	$81, %xmm0, %xmm0
+	ret
+
+in x86-64 mode, we generate this code, which could be better:
+
+_foo2:
+	xorps	%xmm1, %xmm1
+	movss	%xmm0, %xmm1
+	pshufd	$81, %xmm1, %xmm0
+	ret
+
+In sse4 mode, we could use insertps to make both better.
+
+//===---------------------------------------------------------------------===//