simplify-libcalls: fold strncmp(x, y, 1) -> memcmp(x, y, 1)

The memcmp will be optimized further and even the pathological case
'strstr(x, "x") == x' generates optimal code now.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106097 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/SimplifyLibCalls/StrNCmp.ll

@@ -2,6 +2,9 @@
 ; RUN: opt < %s -simplify-libcalls -S | \
 ; RUN:   not grep {call.*strncmp}
 
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128-n8:16:32"
+target triple = "i386-apple-darwin9.0"
+
 @hello = constant [6 x i8] c"hello\00"		; <[6 x i8]*> [#uses=1]
 @hell = constant [5 x i8] c"hell\00"		; <[5 x i8]*> [#uses=1]
 @null = constant [1 x i8] zeroinitializer		; <[1 x i8]*> [#uses=1]
@@ -26,3 +29,7 @@ define i32 @main() {
 	ret i32 %rslt4
 }
 
+define i32 @test1(i8* %P, i8* %Q) {
+  %cmp = call i32 @strncmp(i8* %P, i8* %Q, i32 1)
+  ret i32 %cmp
+}