New entries.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@27473 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index fa37a2a..bc4c19f 100644
--- a/lib/Target/X86/README.txt
+++ b/lib/Target/X86/README.txt
@@ -704,3 +704,59 @@
so a any extend (which becomes a zero extend) is added.
We probably need some kind of target DAG combine hook to fix this.
+
+//===---------------------------------------------------------------------===//
+
+How to decide when to use the "floating point version" of logical ops? Here are
+some code fragments:
+
+ movaps LCPI5_5, %xmm2
+ divps %xmm1, %xmm2
+ mulps %xmm2, %xmm3
+ mulps 8656(%ecx), %xmm3
+ addps 8672(%ecx), %xmm3
+ andps LCPI5_6, %xmm2
+ andps LCPI5_1, %xmm3
+ por %xmm2, %xmm3
+ movdqa %xmm3, (%edi)
+
+ movaps LCPI5_5, %xmm1
+ divps %xmm0, %xmm1
+ mulps %xmm1, %xmm3
+ mulps 8656(%ecx), %xmm3
+ addps 8672(%ecx), %xmm3
+ andps LCPI5_6, %xmm1
+ andps LCPI5_1, %xmm3
+ orps %xmm1, %xmm3
+ movaps %xmm3, 112(%esp)
+ movaps %xmm3, (%ebx)
+
+Due to some minor source change, the later case ended up using orps and movaps
+instead of por and movdqa. Does it matter?
+
+//===---------------------------------------------------------------------===//
+
+Use movddup to splat a v2f64 directly from a memory source. e.g.
+
+#include <emmintrin.h>
+
+void test(__m128d *r, double A) {
+ *r = _mm_set1_pd(A);
+}
+
+llc:
+
+_test:
+ movsd 8(%esp), %xmm0
+ unpcklpd %xmm0, %xmm0
+ movl 4(%esp), %eax
+ movapd %xmm0, (%eax)
+ ret
+
+icc:
+
+_test:
+ movl 4(%esp), %eax
+ movddup 8(%esp), %xmm0
+ movapd %xmm0, (%eax)
+ ret