add some notes

llvm-svn: 25825

llvm/lib/Target/X86/README.txt

@@ -286,3 +286,27 @@ addressing modes.
 
 When compiled with unsafemath enabled, "main" should enable SSE DAZ mode and
 other fast SSE modes.
+
+//===---------------------------------------------------------------------===//
+
+cd Regression/CodeGen/X86
+llvm-as < setuge.ll | llc -march=x86 -mcpu=yonah -enable-x86-sse
+
+_cmp:
+        subl $4, %esp
+1)      leal 20(%esp), %eax
+        movss 12(%esp), %xmm0
+1)      leal 16(%esp), %ecx
+        ucomiss 8(%esp), %xmm0
+        cmovb %ecx, %eax
+2)      movss (%eax), %xmm0
+2)      movss %xmm0, (%esp)
+        flds (%esp)
+        addl $4, %esp
+        ret
+
+
+1) These LEA's should be adds.  This is tricky because they are FrameIndex's
+   before prolog-epilog rewriting.
+2) We shouldn't load into XMM regs only to store it back.
+