instcombine: Migrate strcat and strncat optimizations

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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165874 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/InstCombine/strcat-3.ll

@@ -0,0 +1,22 @@
+; Test that the strcat libcall 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"
+@empty = constant [1 x i8] c"\00"
+@a = common global [32 x i8] zeroinitializer, align 1
+
+declare i16* @strcat(i8*, i8*)
+
+define void @test_nosimplify1() {
+; CHECK: @test_nosimplify1
+; CHECK: call i16* @strcat
+; CHECK: ret void
+
+  %dst = getelementptr [32 x i8]* @a, i32 0, i32 0
+  %src = getelementptr [6 x i8]* @hello, i32 0, i32 0
+  call i16* @strcat(i8* %dst, i8* %src)
+  ret void
+}