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 fa37a2a047f61946c3292623331d39583fb69f29..bc4c19fc92e76c066d719b6c888b647eb3bc70c7 100644 (file)
--- a/lib/Target/X86/README.txt
+++ b/lib/Target/X86/README.txt
@@ -704,3 +704,59 @@ intrisic call and select. 2) The intrinsic is expected to produce a i32 value
 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