Disable frame pointer elimination when -pg is used

[tm]

Summary

This patch disables frame pointer elimination and leaf frame pointer elimination when mcount instrumentation is requested ("-pg").

Currently we catch the case when -fomit-frame-pointer and -pg are explicitly used together, but we miss:

• Explicit use of -momit-leaf-frame-pointer.
• Defaults enabling mentioned optimizations on given optimization level or triple.

This also emits unused argument warnings when -fno-omit-frame-pointer or -mno-omit-leaf-frame-pointer are combined with -pg. It can be changed very simply, but I am not sure if this is desirable or not?

clang -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -pg
clang: warning: argument unused during compilation: '-fno-omit-frame-pointer'
clang: warning: argument unused during compilation: '-mno-omit-leaf-frame-pointer'

[hfinkel]

This also emits unused argument warnings when -fno-omit-frame-pointer or -mno-omit-leaf-frame-pointer are combined with -pg. It can be changed very simply, but I am not sure if this is desirable or not?

This is not desirable. The options are applicable to code generation, and should be processed from the user's perspective (even if they are now redundant). Users often specify options that are technically redundant on certain compiler versions.

[tm]

I have updated patch not to generate unused argument warnings.

[spatel]

Abandon patch?
http://reviews.llvm.org/D14215
http://reviews.llvm.org/rL253886

[spatel]

[I posted this in Phab, but it has not made it to the mailing list.]

Abandon patch?
http://reviews.llvm.org/D14215
http://reviews.llvm.org/rL253886

Also, I linked:
https://llvm.org/bugs/show_bug.cgi?id=14713
https://llvm.org/bugs/show_bug.cgi?id=25535

lib/Driver/Tools.cpp

case llvm::Triple::xcore:
     return false;
   default:
     return true;
   }
 }
 
 static bool shouldUseFramePointer(const ArgList &Args,
                                   const llvm::Triple &Triple) {
+  if (Args.hasArg(options::OPT_pg))
+    return true;
   if (Arg *A = Args.getLastArg(options::OPT_fno_omit_frame_pointer,
                                options::OPT_fomit_frame_pointer))
     return A->getOption().matches(options::OPT_fno_omit_frame_pointer);
 
   return shouldUseFramePointerForTarget(Args, Triple);
 }
 
 static bool shouldUseLeafFramePointer(const ArgList &Args,
                                       const llvm::Triple &Triple) {
+  if (Args.hasArg(options::OPT_pg))
+    return true;
   if (Arg *A = Args.getLastArg(options::OPT_mno_omit_leaf_frame_pointer,
                                options::OPT_momit_leaf_frame_pointer))
     return A->getOption().matches(options::OPT_mno_omit_leaf_frame_pointer);
 
   return shouldUseFramePointerForTarget(Args, Triple);
 }
 
 /// Add a CC1 option to specify the debug compilation directory.
#endif
 
   // Handle the debug info splitting at object creation time if we're
   // creating an object.
   // TODO: Currently only works on linux with newer objcopy.
   if (SplitDwarf && !isa<CompileJobAction>(JA))
     SplitDebugInfo(getToolChain(), C, *this, JA, Args, Output, SplitDwarfOut);
 
   if (Arg *A = Args.getLastArg(options::OPT_pg))
-    if (Args.hasArg(options::OPT_fomit_frame_pointer))
+    if (Arg *Conflict = Args.getLastArg(options::OPT_fomit_frame_pointer,
+                                        options::OPT_momit_leaf_frame_pointer))
       D.Diag(diag::err_drv_argument_not_allowed_with)
-        << "-fomit-frame-pointer" << A->getAsString(Args);
+          << Conflict->getAsString(Args) << A->getAsString(Args);
 
   // Claim some arguments which clang supports automatically.
 
   // -fpch-preprocess is used with gcc to add a special marker in the output to
   // include the PCH file. Clang's PTH solution is completely transparent, so we
   // do not need to deal with it at all.
   Args.ClaimAllArgs(options::OPT_fpch_preprocess);
 

test/Driver/frame-pointer-elim.c

 // RUN: %clang -### -target i386-darwin -S -fomit-frame-pointer %s 2>&1 | \
 // RUN:   FileCheck --check-prefix=OMIT_ALL %s
 // OMIT_ALL-NOT: "-mdisable-fp-elim"
 
 // RUN: %clang -### -target i386-darwin -S -momit-leaf-frame-pointer %s 2>&1 | \
 // RUN:   FileCheck --check-prefix=OMIT_LEAF %s
 // OMIT_LEAF: "-momit-leaf-frame-pointer"
 
+// Disable frame-pointer elimination when -pg is used.
+// RUN: %clang -### -target i386-pc-linux-gnu -S -O2 -pg %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=PG %s
+// RUN: %clang -### -target x86-64-pc-linux-gnu -S -O2 -pg %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=PG %s
+// PG-NOT: "-momit-leaf-frame-pointer"
+// PG:     "-mdisable-fp-elim"
+
+// RUN: %clang -### -target i386-pc-linux-gnu -S -fomit-frame-pointer -pg %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=FOMIT-FRAME-POINTER-PG %s
+// FOMIT-FRAME-POINTER-PG: '-fomit-frame-pointer' not allowed with '-pg'
+
+// RUN: %clang -### -target i386-pc-linux-gnu -S -momit-leaf-frame-pointer -pg %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=MOMIT-LEAF-FRAME-POINTER-PG %s
+// MOMIT-LEAF-FRAME-POINTER-PG: '-momit-leaf-frame-pointer' not allowed with '-pg'
+
 void f0() {}
 void f1() { f0(); }