Do not emit "-tune-cpu generic" for PS4 platform

[dyung]

Summary

For the PS4, do not emit "-tune-cpu generic" since the platform only has 1 known CPU and we do not want to prevent optimizations by tuning for a generic rather than the specific processor it contains.

[probinson]

Couple of nits and LGTM.

clang/lib/Driver/ToolChains/Clang.cpp

2078

Missing final period.

clang/test/Driver/ps4-cpu-defaults.cpp

7

I'd rather see just CHECK-NOT: "-tune-cpu" (without the "generic") . There's no reason for any special tuning.

clang/lib/Driver/ToolChains/Clang.cpp

void Clang::AddX86TargetArgs(const ArgList &Args,
   if (Args.hasFlag(options::OPT_miamcu, options::OPT_mno_iamcu, false)) {
     CmdArgs.push_back("-mfloat-abi");
     CmdArgs.push_back("soft");
     CmdArgs.push_back("-mstack-alignment=4");
   }
 
   // Handle -mtune.
 
-  // Default to "generic" unless -march is present.
+  // Default to "generic" unless -march is present or targetting the PS4.
   std::string TuneCPU;
-  if (!Args.hasArg(clang::driver::options::OPT_march_EQ))
+  if (!Args.hasArg(clang::driver::options::OPT_march_EQ) &&
+      !getToolChain().getTriple().isPS4CPU())
     TuneCPU = "generic";
 
   // Override based on -mtune.
   if (const Arg *A = Args.getLastArg(clang::driver::options::OPT_mtune_EQ)) {
     StringRef Name = A->getValue();
 
     if (Name == "native") {
       Name = llvm::sys::getHostCPUName();

clang/test/Driver/ps4-cpu-defaults.cpp

 // Check that on the PS4 we default to:
-// -target-cpu btver2 and no exceptions
+// -target-cpu btver2, no exceptions and not -tune-cpu generic
 
 // RUN: %clang -target x86_64-scei-ps4 -c %s -### 2>&1 | FileCheck %s
 // CHECK: "-target-cpu" "btver2"
 // CHECK-NOT: exceptions
+// CHECK-NOT: "-tune-cpu"