this xform is implemented.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45404 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/X86/README.txt

@@ -702,28 +702,6 @@ The add\sub pair is really unneeded here.
 
 //===---------------------------------------------------------------------===//
 
-We currently compile sign_extend_inreg into two shifts:
-
-long foo(long X) {
-  return (long)(signed char)X;
-}
-
-becomes:
-
-_foo:
-        movl 4(%esp), %eax
-        shll $24, %eax
-        sarl $24, %eax
-        ret
-
-This could be:
-
-_foo:
-        movsbl  4(%esp),%eax
-        ret
-
-//===---------------------------------------------------------------------===//
-
 Consider the expansion of:
 
 uint %test3(uint %X) {

test/CodeGen/X86/sext-load.ll

@@ -0,0 +1,9 @@
+; RUN: llvm-as < %s | llc -march=x86 | grep movsbl
+
+define i32 @foo(i32 %X) nounwind  {
+entry:
+	%tmp12 = trunc i32 %X to i8		; <i8> [#uses=1]
+	%tmp123 = sext i8 %tmp12 to i32		; <i32> [#uses=1]
+	ret i32 %tmp123
+}
+