[AIX] Fix Link Issue when -fprofile-update=[atomic|prefer-atomic] is in Effect

https://reviews.llvm.org/D157280 enabled `-fprofile-update` for `-fprofile-generate`, but omitted adding `-latomic` to the linker command on AIX. This omission causes linking to fail due to an undefined symbol. This patch fixes the link error.

Reviewed By: w2yehia

Differential Revision: https://reviews.llvm.org/D159137

Author: Qiongsi Wu

clang/lib/Driver/ToolChains/AIX.cpp

@@ -429,11 +429,20 @@ void AIX::addClangTargetOptions(
 
 void AIX::addProfileRTLibs(const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs) const {
-  // Add linker option -u__llvm_profile_runtime to cause runtime
-  // initialization to occur.
-  if (needsProfileRT(Args))
+  if (needsProfileRT(Args)) {
+    // Add linker option -u__llvm_profile_runtime to cause runtime
+    // initialization to occur.
     CmdArgs.push_back(Args.MakeArgString(
         Twine("-u", llvm::getInstrProfRuntimeHookVarName())));
+
+    if (const auto *A =
+            Args.getLastArgNoClaim(options::OPT_fprofile_update_EQ)) {
+      StringRef Val = A->getValue();
+      if (Val == "atomic" || Val == "prefer-atomic")
+        CmdArgs.push_back("-latomic");
+    }
+  }
+
   ToolChain::addProfileRTLibs(Args, CmdArgs);
 }
 

clang/test/Driver/fprofile-update.c

@@ -12,3 +12,11 @@
 // RUN: not %clang %s -c -fprofile-update=unknown 2>&1 | FileCheck %s --check-prefix=ERROR
 
 // ERROR: error: unsupported argument 'unknown' to option '-fprofile-update='
+
+// AIX specific tests
+// RUN: %clang -### %s --target=powerpc-unknown-aix -fprofile-generate -fprofile-update=atomic 2>&1 | FileCheck %s --check-prefix=AIX
+// RUN: %clang -### %s --target=powerpc-unknown-aix -fprofile-generate -fprofile-update=prefer-atomic 2>&1 | FileCheck %s --check-prefix=AIX
+// RUN: %clang -### %s --target=powerpc-unknown-aix -fprofile-generate 2>&1 | FileCheck %s --check-prefix=AIX-NOATOMIC
+// RUN: %clang -### %s --target=powerpc-unknown-aix -fprofile-generate -fprofile-update=single 2>&1 | FileCheck %s --check-prefix=AIX-NOATOMIC
+// AIX: "-latomic"
+// AIX-NOATOMIC-NOT: "-latomic"