add a note
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@27567 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index 9db0cef..f9d3643 100644
--- a/lib/Target/X86/README.txt
+++ b/lib/Target/X86/README.txt
@@ -675,6 +675,29 @@
//===---------------------------------------------------------------------===//
+Better codegen for:
+
+void f(float a, float b, vector float * out) { *out = (vector float){ a, 0.0, 0.0, b}; }
+void f(float a, float b, vector float * out) { *out = (vector float){ a, b, 0.0, 0}; }
+
+For the later we generate:
+
+_f:
+ pxor %xmm0, %xmm0
+ movss 8(%esp), %xmm1
+ movaps %xmm0, %xmm2
+ unpcklps %xmm1, %xmm2
+ movss 4(%esp), %xmm1
+ unpcklps %xmm0, %xmm1
+ unpcklps %xmm2, %xmm1
+ movl 12(%esp), %eax
+ movaps %xmm1, (%eax)
+ ret
+
+This seems like it should use shufps, one for each of a & b.
+
+//===---------------------------------------------------------------------===//
+
Adding to the list of cmp / test poor codegen issues:
int test(__m128 *A, __m128 *B) {