X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTarget%2FX86%2FREADME-MMX.txt;h=a6c8616b6d2c6b77a897de92552ef3111b20d25b;hb=1292c226458b68a119d3a387a0527f453b2065c2;hp=f3a625e65dc6be78c6969bb0ffbf30424ea524f0;hpb=a2c38ae90db202c50cfd290983189482497b0851;p=oota-llvm.git

diff --git a/lib/Target/X86/README-MMX.txt b/lib/Target/X86/README-MMX.txt
index f3a625e65dc..a6c8616b6d2 100644
--- a/lib/Target/X86/README-MMX.txt
+++ b/lib/Target/X86/README-MMX.txt
@@ -40,3 +40,32 @@ _qux:
         movl    %edx, 4(%eax)
         addl    $12, %esp
         ret     $4
+
+//===---------------------------------------------------------------------===//
+
+We generate crappy code for this:
+
+__m64 t() {
+  return _mm_cvtsi32_si64(1);
+}
+
+_t:
+	subl	$12, %esp
+	movl	$1, %eax
+	movd	%eax, %mm0
+	movq	%mm0, (%esp)
+	movl	(%esp), %eax
+	movl	4(%esp), %edx
+	addl	$12, %esp
+	ret
+
+The extra stack traffic is covered in the previous entry. But the other reason
+is we are not smart about materializing constants in MMX registers. With -m64
+
+	movl	$1, %eax
+	movd	%eax, %mm0
+	movd	%mm0, %rax
+	ret
+
+We should be using a constantpool load instead:
+	movq	LC0(%rip), %rax