[Hexagon] Select lld as the default linker for linux-musl target

[sidneym]

Summary

When the target is hexagon-unknown-linux-musl select lld as the default linker.

[nathanchance]

This does not take into account CLANG_DEFAULT_LINKER, resulting in a check-clang failure:

$ cmake -GNinja \
              -DCMAKE_C_COMPILER=clang \
              -DCMAKE_CXX_COMPILER=clang++ \
              -DLLVM_ENABLE_PROJECTS=clang \
              -DPYTHON_EXECUTABLE=$(command -v python3) \
              ../llvm && ninja check-clang
...
Testing Time: 163.80s
  Expected Passes    : 17055
  Expected Failures  : 23
  Unsupported Tests  : 55

$ cmake -GNinja \
              -DCMAKE_C_COMPILER=clang \
              -DCMAKE_CXX_COMPILER=clang++ \
              -DLLVM_ENABLE_PROJECTS=clang \
              -DPYTHON_EXECUTABLE=$(command -v python3) \
              -DCLANG_DEFAULT_LINKER=lld \
              ../llvm && ninja check-clang
...
Testing Time: 176.55s
********************
Failing Tests (1):
    Clang :: Driver/hexagon-toolchain-elf.c

  Expected Passes    : 17050
  Expected Failures  : 23
  Unsupported Tests  : 59
  Unexpected Failures: 1

[bcain]

In D77498#1967870, @nathanchance wrote:

This does not take into account CLANG_DEFAULT_LINKER, resulting in a check-clang failure:

Weird -- the baseline didn't take CLANG_DEFAULT_LINKER into account either, though, right? Is it a regression?

[nathanchance]

Weird -- the baseline didn't take CLANG_DEFAULT_LINKER into account either, though, right?

I assume by baseline you mean the test before this change? It does not seem like it.

Is it a regression?

I guess not but the test is still broken when CLANG_DEFAULT_LINKER is set.

[sidneym]

These are new tests how do you get the generic lld driver to work? When I invoke it using just "lld" I need to add -flavor gnu or I get this error:
Invoke ld.lld (Unix), ld64.lld (macOS), lld-link (Windows), wasm-ld (WebAssembly) instead

[sidneym]

Since this isn't something that can be always known in advance I think the testcase should just be removed.

[bcain]

In D77498#1968123, @sidneym wrote:

Since this isn't something that can be always known in advance I think the testcase should just be removed.

Why not just check if CLANG_DEFAULT_LINKER is empty?

const char *getDefaultLinker() const override {
    StringRef ClangDefault = CLANG_DEFAULT_LINKER;
    return ClangDefault.isEmpty() ? (getTriple().isMusl() ? "ld.lld" : "hexagon-link") : ClangDefault.str();
  }

[nathanchance]

These are new tests how do you get the generic lld driver to work?

It doesn't, Clang invokes the appropriate driver in ToolChain::GetLinkerPath(): https://github.com/llvm/llvm-project/blob/6011627f5118dd64a0c33694b604c70e766d8c40/clang/lib/Driver/ToolChain.cpp#L537-L541

clang/lib/Driver/ToolChains/Hexagon.h

void addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
                              Action::OffloadKind DeviceOffloadKind) const override;
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
   void addLibStdCxxIncludePaths(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override;
 
-  const char *getDefaultLinker() const override { return "hexagon-link"; }
+  const char *getDefaultLinker() const override {
+    return getTriple().isMusl() ? "ld.lld" : "hexagon-link";
+  }
 
   CXXStdlibType GetCXXStdlibType(const llvm::opt::ArgList &Args) const override;
 
   StringRef GetGCCLibAndIncVersion() const { return GCCLibAndIncVersion.Text; }
   bool IsIntegratedAssemblerDefault() const override {
     return true;
   }
 

clang/test/Driver/hexagon-toolchain-elf.c

 // -----------------------------------------------------------------------------
 // RUN: %clang -### -target hexagon-unknown-linux-musl \
 // RUN:   -ccc-install-dir %S/Inputs/hexagon_tree/Tools/bin \
 // RUN:   -mcpu=hexagonv60 \
 // RUN:   %s 2>&1 \
 // RUN:   | FileCheck -check-prefix=CHECK090 %s
 // CHECK090-NOT:          -fno-use-init-array
 // -----------------------------------------------------------------------------
+// Check default linker for musl
+// -----------------------------------------------------------------------------
+// RUN: %clang -### -target hexagon-unknown-linux-musl %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK091 %s
+// CHECK091:          ld.lld
+// -----------------------------------------------------------------------------
+// Check default linker for elf
+// -----------------------------------------------------------------------------
+// RUN: %clang -### -target hexagon-unknown-elf %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK092 %s
+// CHECK092:          hexagon-link
+// -----------------------------------------------------------------------------