[PPC] Enable -fomit-frame-pointer by default for PPC

[inouehrs]

Summary

This patch enables -fomit-frame-pointer option by default for PowerPC if -O1 or above optimization level is specified.
GCC already enables this option by default for -O1 or above in all of ppc32, ppc64 and ppc64le.
This option gives some performance improvements in many programs by reducing the overhead in method prologue and epilogue.

[hfinkel]

We should have regression tests for this. Maybe update test/Driver/frame-pointer-elim.c?

[inouehrs]

Thank you for the comment.
I added regression tests for PPC in test/Driver/frame-pointer.c as for other platforms.

[hfinkel]

LGTM

lib/Driver/Tools.cpp

static bool useFramePointerForTargetByDefault(const ArgList &Args,
 
   if (Triple.isOSLinux() || Triple.getOS() == llvm::Triple::CloudABI) {
     switch (Triple.getArch()) {
     // Don't use a frame pointer on linux if optimizing for certain targets.
     case llvm::Triple::mips64:
     case llvm::Triple::mips64el:
     case llvm::Triple::mips:
     case llvm::Triple::mipsel:
+    case llvm::Triple::ppc:
+    case llvm::Triple::ppc64:
+    case llvm::Triple::ppc64le:
     case llvm::Triple::systemz:
     case llvm::Triple::x86:
     case llvm::Triple::x86_64:
       return !areOptimizationsEnabled(Args);
     default:
       return true;
     }
   }