[Clang] Set -mlinker-version explicitly in the lto test

[phosek]

Summary

This test assumes that the driver will set -object_path_lto linker
flag and it requests the platform linker with -fuse-ld=. When lld is
used as the host linker, the host linker version is unset and so
Clang won't set -object_path_lto since that flag is set conditionally
only when linker version is at least 116. We set the linker version
explicitly to make sure that -object_path_lto is set. That approach
is already used elsewhere in the test.

[int3]

Would it make sense to have clang pass -object_path_lto whenever it's invoking LLD?

[phosek]

In D122110#3395336, @int3 wrote:

Would it make sense to have clang pass -object_path_lto whenever it's invoking LLD?

It already does, see https://github.com/llvm/llvm-project/blob/afc2f024462951d6e74c5e733f4b4666e21d3309/clang/lib/Driver/ToolChains/Darwin.cpp#L232, but in this particular case the test is explicitly requesting the platform linker by passing -fuse-ld=.

[int3]

Ohh gotcha. So clang assumes that the platform linker's version is at least as high as the host linker's, assuming the host linker is ld64. That seems kind of hacky, but I suppose it's existing behavior...

[phosek]

In D122110#3395427, @int3 wrote:

Ohh gotcha. So clang assumes that the platform linker's version is at least as high as the host linker's, assuming the host linker is ld64. That seems kind of hacky, but I suppose it's existing behavior...

I agree, I don't think that the version of the host linker on the system where Clang was built should affect driver's behavior. Ideally, Clang would check the linker version dynamically but that would be a change to the existing behavior and I don't know if that would cause problems.

clang/test/Driver/darwin-ld-lto.c

 // Also pass -lto_library even if the file doesn't exist; if it's needed at
 // link time, ld will complain instead.
 // RUN: %clang -fuse-ld= -target x86_64-apple-darwin10 -### %s \
 // RUN:   -ccc-install-dir %S/dummytestdir -mlinker-version=133 2> %t.log
 // RUN: FileCheck -check-prefix=LINK_LTOLIB_PATH %s -input-file %t.log
 
 
 // Check that -object_lto_path is passed correctly to ld64
-// RUN: %clang -fuse-ld= -target x86_64-apple-darwin10 %s -flto=full -### 2>&1 \
+// RUN: %clang -fuse-ld= -target x86_64-apple-darwin10 %s -flto=full \
+// RUN:     -mlinker-version=116 -### 2>&1 \
 // RUN:     | FileCheck -check-prefix=FULL_LTO_OBJECT_PATH %s
 // FULL_LTO_OBJECT_PATH: {{ld(.exe)?"}}
 // FULL_LTO_OBJECT_PATH-SAME: "-object_path_lto"
 // FULL_LTO_OBJECT_PATH-SAME: {{cc\-[a-zA-Z0-9_]+.o}}"
-// RUN: %clang -fuse-ld= -target x86_64-apple-darwin10 %s -flto=thin -### 2>&1 \
+// RUN: %clang -fuse-ld= -target x86_64-apple-darwin10 %s -flto=thin \
+// RUN:     -mlinker-version=116 -### 2>&1 \
 // RUN:     | FileCheck -check-prefix=THIN_LTO_OBJECT_PATH %s
 // THIN_LTO_OBJECT_PATH: {{ld(.exe)?"}}
 // THIN_LTO_OBJECT_PATH-SAME: "-object_path_lto"
 // THIN_LTO_OBJECT_PATH-SAME: {{thinlto\-[a-zA-Z0-9_]+}}
 
 
 // Check that we pass through -fglobal-isel flags to libLTO.
 // RUN: %clang -target arm64-apple-darwin %s -flto -fglobal-isel -### 2>&1 | \
 // RUN:   FileCheck --check-prefix=GISEL %s
 // GISEL: {{ld(.exe)?"}}
 // GISEL: "-mllvm" "-global-isel"
 // GISEL: "-mllvm" "-global-isel-abort=0"