instcombine: Migrate strlen optimizations

This patch migrates the strlen optimizations from the simplify-libcalls
pass into the instcombine library call simplifier.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167103 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/InstCombine/strlen-2.ll

@@ -0,0 +1,18 @@
+; Test that the strlen library call simplifier works correctly.
+;
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+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"
+
+@hello = constant [6 x i8] c"hello\00"
+
+declare i32 @strlen(i8*, i32)
+
+define i32 @test_no_simplify1() {
+; CHECK: @test_no_simplify1
+  %hello_p = getelementptr [6 x i8]* @hello, i32 0, i32 0
+  %hello_l = call i32 @strlen(i8* %hello_p, i32 187)
+; CHECK-NEXT: %hello_l = call i32 @strlen
+  ret i32 %hello_l
+; CHECK-NEXT: ret i32 %hello_l
+}