[Driver] Use libatomic for 32-bit SPARC atomics support

Even after D86621 <https://reviews.llvm.org/D86621>, `clang -m32` on
Solaris/sparcv9 doesn't inline atomics with 8-byte operands, unlike `gcc`.
This leads to many link failures in the testsuite (undefined references to
`__atomic_load_8` and `__sync_val_compare_and_swap_8`.  Until a proper
codegen fix can be implemented, this patch works around the first of those
by linking with `-latomic`.

Tested on `sparcv9-sun-solaris2.11`.

Differential Revision: https://reviews.llvm.org/D118021

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -756,7 +756,7 @@ static bool addSanitizerDynamicList(const ToolChain &TC, const ArgList &Args,
   return false;
 }
 
-static const char *getAsNeededOption(const ToolChain &TC, bool as_needed) {
+const char *tools::getAsNeededOption(const ToolChain &TC, bool as_needed) {
   assert(!TC.getTriple().isOSAIX() &&
          "AIX linker does not support any form of --as-needed option yet.");
 

clang/lib/Driver/ToolChains/CommonArgs.h

@@ -117,6 +117,8 @@ bool addOpenMPRuntime(llvm::opt::ArgStringList &CmdArgs, const ToolChain &TC,
                       bool ForceStaticHostRuntime = false,
                       bool IsOffloadingHost = false, bool GompNeedsRT = false);
 
+const char *getAsNeededOption(const ToolChain &TC, bool as_needed);
+
 llvm::opt::Arg *getLastProfileUseArg(const llvm::opt::ArgList &Args);
 llvm::opt::Arg *getLastProfileSampleUseArg(const llvm::opt::ArgList &Args);
 

clang/lib/Driver/ToolChains/Solaris.cpp

@@ -132,6 +132,13 @@ void solaris::Linker::ConstructJob(Compilation &C, const JobAction &JA,
       CmdArgs.push_back("-lssp_nonshared");
       CmdArgs.push_back("-lssp");
     }
+    // LLVM support for atomics on 32-bit SPARC V8+ is incomplete, so
+    // forcibly link with libatomic as a workaround.
+    if (getToolChain().getTriple().getArch() == llvm::Triple::sparc) {
+      CmdArgs.push_back(getAsNeededOption(getToolChain(), true));
+      CmdArgs.push_back("-latomic");
+      CmdArgs.push_back(getAsNeededOption(getToolChain(), false));
+    }
     CmdArgs.push_back("-lgcc_s");
     CmdArgs.push_back("-lc");
     if (!Args.hasArg(options::OPT_shared)) {

clang/test/Driver/solaris-ld.c

@@ -17,6 +17,7 @@
 // CHECK-LD-SPARC32-SAME: "-L[[SYSROOT]]/usr/gcc/4.8/lib/gcc/sparc-sun-solaris2.11/4.8.2"
 // CHECK-LD-SPARC32-SAME: "-L[[SYSROOT]]/usr/gcc/4.8/lib/gcc/sparc-sun-solaris2.11/4.8.2/../../.."
 // CHECK-LD-SPARC32-SAME: "-L[[SYSROOT]]/usr/lib"
+// CHECK-LD-SPARC32-SAME: "-zignore" "-latomic" "-zrecord"
 // CHECK-LD-SPARC32-SAME: "-lgcc_s"
 // CHECK-LD-SPARC32-SAME: "-lc"
 // CHECK-LD-SPARC32-SAME: "-lgcc"
@@ -40,6 +41,7 @@
 // CHECK-LD-SPARC64-SAME: "-L[[SYSROOT]]/usr/gcc/4.8/lib/gcc/sparc-sun-solaris2.11/4.8.2/sparcv9"
 // CHECK-LD-SPARC64-SAME: "-L[[SYSROOT]]/usr/gcc/4.8/lib/gcc/sparc-sun-solaris2.11/4.8.2/../../../sparcv9"
 // CHECK-LD-SPARC64-SAME: "-L[[SYSROOT]]/usr/lib/sparcv9"
+// CHECK-LD-SPARC64-NOT:  "-latomic"
 // CHECK-LD-SPARC64-SAME: "-lgcc_s"
 // CHECK-LD-SPARC64-SAME: "-lc"
 // CHECK-LD-SPARC64-SAME: "-lgcc"
@@ -63,6 +65,7 @@
 // CHECK-LD-X32-SAME: "-L[[SYSROOT]]/usr/gcc/4.9/lib/gcc/i386-pc-solaris2.11/4.9.4"
 // CHECK-LD-X32-SAME: "-L[[SYSROOT]]/usr/gcc/4.9/lib/gcc/i386-pc-solaris2.11/4.9.4/../../.."
 // CHECK-LD-X32-SAME: "-L[[SYSROOT]]/usr/lib"
+// CHECK-LD-X32-NOT:  "-latomic"
 // CHECK-LD-X32-SAME: "-lgcc_s"
 // CHECK-LD-X32-SAME: "-lc"
 // CHECK-LD-X32-SAME: "-lgcc"
@@ -86,6 +89,7 @@
 // CHECK-LD-X64-SAME: "-L[[SYSROOT]]/usr/gcc/4.9/lib/gcc/i386-pc-solaris2.11/4.9.4/amd64"
 // CHECK-LD-X64-SAME: "-L[[SYSROOT]]/usr/gcc/4.9/lib/gcc/i386-pc-solaris2.11/4.9.4/../../../amd64"
 // CHECK-LD-X64-SAME: "-L[[SYSROOT]]/usr/lib/amd64"
+// CHECK-LD-X64-NOT:  "-latomic"
 // CHECK-LD-X64-SAME: "-lgcc_s"
 // CHECK-LD-X64-SAME: "-lc"
 // CHECK-LD-X64-SAME: "-lgcc"