CodeGen: Replace test/CodeGen/thinlto_backend.c with a functional test.

[pcc]

Summary

This new test tests that functions are capable of being imported, rather than
that the import pass is run. This new test is compatible with the approach
being developed in D20268 which runs the importer on its own rather than in
a pass.

[tejohnson]

LGTM but with one question: Any issue with IR tests in clang tests? I noticed that there are very few (although there is already one existing .ll in test/CodeGen).

[pcc]

Should be fine. This is testing an unusual feature of clang that takes IR as input, so IR is the appropriate input type here.

[echristo]

Why is this in clang rather than in llvm?

[pcc]

This is testing a clang feature that reads IR and runs the ThinLTO backend. This feature is part of ThinLTO's distributed build support (search for "Distributed Build Support" in http://blog.llvm.org/2016/06/thinlto-scalable-and-incremental-lto.html).

In a future change I want to replace the clang-side code here with a client of a new LTO interface that takes IR and produces object files (see D21545). So I think testing the object file is the right approach here.

[echristo]

OK, that works for me. :)

cfe/trunk/test/CodeGen/Inputs/thinlto_backend.ll

+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @f2() {
+  ret void
+}

cfe/trunk/test/CodeGen/thinlto_backend.c

-// RUN: %clang -O2 %s -flto=thin -c -o %t.o
-// RUN: llvm-lto -thinlto -o %t %t.o
-
-// Ensure clang -cc1 give expected error for incorrect input type
-// RUN: not %clang_cc1 -O2 -o %t1.o %s -c -fthinlto-index=%t.thinlto.bc 2>&1 | FileCheck %s -check-prefix=CHECK-WARNING
-// CHECK-WARNING: error: invalid argument '-fthinlto-index={{.*}}' only allowed with '-x ir'
-
-// Ensure we get expected error for missing index file
-// RUN: %clang -O2 -o %t1.o -x ir %t.o -c -fthinlto-index=bad.thinlto.bc 2>&1 | FileCheck %s -check-prefix=CHECK-ERROR
-// CHECK-ERROR: Error loading index file 'bad.thinlto.bc'
-
-// Ensure Function Importing pass added
-// RUN: %clang -O2 -o %t1.o -x ir %t.o -c -fthinlto-index=%t.thinlto.bc -mllvm -debug-pass=Structure 2>&1 | FileCheck %s -check-prefix=CHECK-PASS
-// CHECK-PASS: Function Importing

cfe/trunk/test/CodeGen/thinlto_backend.ll

+; RUN: opt -module-summary -o %t1.o %s
+; RUN: opt -module-summary -o %t2.o %S/Inputs/thinlto_backend.ll
+; RUN: llvm-lto -thinlto -o %t %t1.o %t2.o
+
+; Ensure clang -cc1 give expected error for incorrect input type
+; RUN: not %clang_cc1 -O2 -o %t1.o -x c %s -c -fthinlto-index=%t.thinlto.bc 2>&1 | FileCheck %s -check-prefix=CHECK-WARNING
+; CHECK-WARNING: error: invalid argument '-fthinlto-index={{.*}}' only allowed with '-x ir'
+
+; Ensure we get expected error for missing index file
+; RUN: %clang -O2 -o %t3.o -x ir %t1.o -c -fthinlto-index=bad.thinlto.bc 2>&1 | FileCheck %s -check-prefix=CHECK-ERROR
+; CHECK-ERROR: Error loading index file 'bad.thinlto.bc'
+
+; Ensure f2 was imported
+; RUN: %clang -O2 -o %t3.o -x ir %t1.o -c -fthinlto-index=%t.thinlto.bc
+; RUN: llvm-nm %t3.o | FileCheck --check-prefix=CHECK-OBJ %s
+; CHECK-OBJ: T f1
+; CHECK-OBJ-NOT: U f2
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare void @f2()
+
+define void @f1() {
+  call void @f2()
+  ret void
+}