[mips] Add '-mrelax-pic-calls', '-mno-relax-pic-calls'

[vstefanovic]

Summary

These two options enable/disable emission of R_{MICRO}MIPS_JALR fixups along
with PIC calls. The linker may then try to turn PIC calls into direct jumps.
By default, these fixups do get emitted by the backend, use
'-mno-relax-pic-calls' to omit them.

[atanasyan]

LGTM with a nit.

lib/Driver/ToolChains/Clang.cpp

1720 ↗

(On Diff #182397)

It's not necessary to call the MakeArgString here. You can write just CmdArgs.push_back("-mips-jalr-reloc=0");.

[sdardis]

cfe/trunk/include/clang/Driver/Options.td

2423

I think this help text could be a little better. Instead of implying that the compiler could turn PIC calls into direct calls, something like "Produce relaxation hints for linkers to try optimizing PIC call sequences into direct calls", I believe describes the optimization better. Likewise in the negative sense for the -mno-relax-pic-calls.

[vstefanovic]

cfe/trunk/include/clang/Driver/Options.td

2423

Hi Simon, I'll replace the text with your version, it's better indeed. Thanks.

cfe/trunk/include/clang/Driver/Options.td

def mfpxx : Flag<["-"], "mfpxx">, Group<m_mips_Features_Group>,
   HelpText<"Avoid FPU mode dependent operations when used with the O32 ABI">,
   Flags<[HelpHidden]>;
 def modd_spreg : Flag<["-"], "modd-spreg">, Group<m_mips_Features_Group>,
   HelpText<"Enable odd single-precision floating point registers">,
   Flags<[HelpHidden]>;
 def mno_odd_spreg : Flag<["-"], "mno-odd-spreg">, Group<m_mips_Features_Group>,
   HelpText<"Disable odd single-precision floating point registers">,
   Flags<[HelpHidden]>;
+def mrelax_pic_calls : Flag<["-"], "mrelax-pic-calls">,
+  Group<m_mips_Features_Group>,
+  HelpText<"Try turning PIC calls (j{al}r{c} $25) into direct calls "
+  "(MIPS only)">, Flags<[HelpHidden]>;
+def mno_relax_pic_calls : Flag<["-"], "mno-relax-pic-calls">,
+  Group<m_mips_Features_Group>,
+  HelpText<"Do not try turning PIC calls (j{al}r{c} $25) into direct calls "
+  "(MIPS only)">, Flags<[HelpHidden]>;
 def mglibc : Flag<["-"], "mglibc">, Group<m_libc_Group>, Flags<[HelpHidden]>;
 def muclibc : Flag<["-"], "muclibc">, Group<m_libc_Group>, Flags<[HelpHidden]>;
 def module_file_info : Flag<["-"], "module-file-info">, Flags<[DriverOption,CC1Option]>, Group<Action_Group>,
   HelpText<"Provide information about a particular module file">;
 def mthumb : Flag<["-"], "mthumb">, Group<m_Group>;
 def mtune_EQ : Joined<["-"], "mtune=">, Group<m_Group>;
 def multi__module : Flag<["-"], "multi_module">;
 def multiply__defined__unused : Separate<["-"], "multiply_defined_unused">;

cfe/trunk/lib/Driver/ToolChains/Clang.cpp

if (mips::hasCompactBranches(CPUName)) {
         CmdArgs.push_back("-mllvm");
         CmdArgs.push_back(Args.MakeArgString("-mips-compact-branches=" + Val));
       } else
         D.Diag(diag::err_drv_unsupported_option_argument)
             << A->getOption().getName() << Val;
     } else
       D.Diag(diag::warn_target_unsupported_compact_branches) << CPUName;
   }
+
+  if (Arg *A = Args.getLastArg(options::OPT_mrelax_pic_calls,
+                               options::OPT_mno_relax_pic_calls)) {
+    if (A->getOption().matches(options::OPT_mno_relax_pic_calls)) {
+      CmdArgs.push_back("-mllvm");
+      CmdArgs.push_back("-mips-jalr-reloc=0");
+    }
+  }
 }
 
 void Clang::AddPPCTargetArgs(const ArgList &Args,
                              ArgStringList &CmdArgs) const {
   // Select the ABI to use.
   const char *ABIName = nullptr;
   if (getToolChain().getTriple().isOSLinux())
     switch (getToolChain().getArch()) {

cfe/trunk/test/Driver/mips-features.c

 // RUN:   | FileCheck --check-prefix=CHECK-GINV %s
 // CHECK-GINV: "-target-feature" "+ginv"
 //
 // -mno-ginv
 // RUN: %clang -target mips-unknown-linux-gnu -### -c %s \
 // RUN:     -mginv -mno-ginv 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-GINV %s
 // CHECK-NO-GINV: "-target-feature" "-ginv"
+//
+// -mrelax-pic-calls
+// RUN: %clang -target mips-unknown-linux-gnu -### -c %s \
+// RUN:     -mno-relax-pic-calls -mrelax-pic-calls 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-RELAX-PIC-CALLS %s
+// CHECK-RELAX-PIC-CALLS-NOT: "-mllvm" "-mips-jalr-reloc=0"
+//
+// -mno-relax-pic-calls
+// RUN: %clang -target mips-unknown-linux-gnu -### -c %s \
+// RUN:     -mrelax-pic-calls -mno-relax-pic-calls 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-RELAX-PIC-CALLS %s
+// CHECK-NO-RELAX-PIC-CALLS: "-mllvm" "-mips-jalr-reloc=0"