[mips] Compact branch policy setting

[sdardis]

Summary

This patch adds the commandline option -mcompact-branches={never,optimal,always),
which controls how LLVM generates compact branches for MIPSR6 targets. By default,
the compact branch policy is 'optimal' where LLVM will generate the most
appropriate branch for any situation. The 'never' and 'always' policy will disable
or always generate compact branches wherever possible respectfully.

[atanasyan]

LGTM with some nits

lib/Driver/Tools.cpp

1446 ↗

(On Diff #58778)

Redundant empty line.

7084 ↗

(On Diff #58778)

Redundant empty line.

7085 ↗

(On Diff #58778)

Is it possible to re-write this line as:

return llvm::StringSwitch<bool>(CPU)

[sdardis]

Thanks for the review.

cfe/trunk/docs/UsersManual.rst

 
 .. option:: -mgeneral-regs-only
 
    Generate code which only uses the general purpose registers.
 
    This option restricts the generated code to use general registers
    only. This only applies to the AArch64 architecture.
 
+.. option:: -mcompact-branches=[values]
+
+   Control the usage of compact branches for MIPSR6.
+
+   Valid values are: ``never``, ``optimal`` and ``always``.
+   The default value is ``optimal`` which generates compact branches
+   when a delay slot cannot be filled. ``never`` disables the usage of
+   compact branches and ``always`` generates compact branches whenever
+   possible.
+
 **-f[no-]max-type-align=[number]**
    Instruct the code generator to not enforce a higher alignment than the given
    number (of bytes) when accessing memory via an opaque pointer or reference.
    This cap is ignored when directly accessing a variable or when the pointee
    type has an explicit “aligned” attribute.
 
    The value should usually be determined by the properties of the system allocator.
    Some builtin types, especially vector types, have very high natural alignments;

cfe/trunk/include/clang/Basic/DiagnosticDriverKinds.td

def warn_drv_invoking_fallback : Warning<"falling back to %0">,
   InGroup<Fallback>;
 
 def warn_target_unsupported_nan2008 : Warning<
   "ignoring '-mnan=2008' option because the '%0' architecture does not support it">,
   InGroup<UnsupportedNan>;
 def warn_target_unsupported_nanlegacy : Warning<
   "ignoring '-mnan=legacy' option because the '%0' architecture does not support it">,
   InGroup<UnsupportedNan>;
+def warn_target_unsupported_compact_branches : Warning<
+  "ignoring '-mcompact-branches=' option because the '%0' architecture does not"
+  " support it">, InGroup<UnsupportedCB>;
 
 def warn_drv_unable_to_find_directory_expected : Warning<
   "unable to find %0 directory, expected to be in '%1'">,
   InGroup<InvalidOrNonExistentDirectory>, DefaultIgnore;
 
 def warn_drv_ps4_force_pic : Warning<
   "option '%0' was ignored by the PS4 toolchain, using '-fPIC'">,
   InGroup<OptionIgnored>;
 
 def warn_drv_ps4_sdk_dir : Warning<
   "environment variable SCE_ORBIS_SDK_DIR is set, but points to invalid or nonexistent directory '%0'">,
   InGroup<InvalidOrNonExistentDirectory>;
 
 def err_drv_unsupported_linker : Error<"unsupported value '%0' for -linker option">;
 }

cfe/trunk/include/clang/Basic/DiagnosticGroups.td

 def FloatZeroConversion : DiagGroup<"float-zero-conversion">;
 def FloatConversion :
   DiagGroup<"float-conversion", [FloatOverflowConversion,
                                  FloatZeroConversion]>;
 
 def DoublePromotion : DiagGroup<"double-promotion">;
 def EnumTooLarge : DiagGroup<"enum-too-large">;
 def UnsupportedNan : DiagGroup<"unsupported-nan">;
+def UnsupportedCB : DiagGroup<"unsupported-cb">;
 def NonLiteralNullConversion : DiagGroup<"non-literal-null-conversion">;
 def NullConversion : DiagGroup<"null-conversion">;
 def ImplicitConversionFloatingPointToBool :
   DiagGroup<"implicit-conversion-floating-point-to-bool">;
 def ObjCLiteralConversion : DiagGroup<"objc-literal-conversion">;
 def BadArrayNewLength : DiagGroup<"bad-array-new-length">;
 def MacroRedefined : DiagGroup<"macro-redefined">;
 def BuiltinMacroRedefined : DiagGroup<"builtin-macro-redefined">;

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

 def mno_micromips : Flag<["-"], "mno-micromips">, Group<m_Group>;
 def mxgot : Flag<["-"], "mxgot">, Group<m_Group>;
 def mno_xgot : Flag<["-"], "mno-xgot">, Group<m_Group>;
 def mldc1_sdc1 : Flag<["-"], "mldc1-sdc1">, Group<m_Group>;
 def mno_ldc1_sdc1 : Flag<["-"], "mno-ldc1-sdc1">, Group<m_Group>;
 def mcheck_zero_division : Flag<["-"], "mcheck-zero-division">, Group<m_Group>;
 def mno_check_zero_division : Flag<["-"], "mno-check-zero-division">,
                               Group<m_Group>;
+def mcompact_branches_EQ : Joined<["-"], "mcompact-branches=">, Group<m_Group>;
 def mdsp : Flag<["-"], "mdsp">, Group<m_Group>;
 def mno_dsp : Flag<["-"], "mno-dsp">, Group<m_Group>;
 def mdspr2 : Flag<["-"], "mdspr2">, Group<m_Group>;
 def mno_dspr2 : Flag<["-"], "mno-dspr2">, Group<m_Group>;
 def msingle_float : Flag<["-"], "msingle-float">, Group<m_Group>;
 def mdouble_float : Flag<["-"], "mdouble-float">, Group<m_Group>;
 def mmsa : Flag<["-"], "mmsa">, Group<m_Group>,
   HelpText<"Enable MSA ASE (MIPS only)">;

cfe/trunk/lib/Driver/Tools.h

 
 enum class FloatABI {
   Invalid,
   Soft,
   Hard,
 };
 
 NanEncoding getSupportedNanEncoding(StringRef &CPU);
+bool hasCompactBranches(StringRef &CPU);
 void getMipsCPUAndABI(const llvm::opt::ArgList &Args,
                       const llvm::Triple &Triple, StringRef &CPUName,
                       StringRef &ABIName);
 std::string getMipsABILibSuffix(const llvm::opt::ArgList &Args,
                                 const llvm::Triple &Triple);
 bool hasMipsAbiArg(const llvm::opt::ArgList &Args, const char *Value);
 bool isUCLibc(const llvm::opt::ArgList &Args);
 bool isNaN2008(const llvm::opt::ArgList &Args, const llvm::Triple &Triple);

cfe/trunk/lib/Driver/Tools.cpp

void Clang::AddMIPSTargetArgs(const ArgList &Args,
   }
 
   if (Arg *A = Args.getLastArg(options::OPT_G)) {
     StringRef v = A->getValue();
     CmdArgs.push_back("-mllvm");
     CmdArgs.push_back(Args.MakeArgString("-mips-ssection-threshold=" + v));
     A->claim();
   }
+
+  if (Arg *A = Args.getLastArg(options::OPT_mcompact_branches_EQ)) {
+    StringRef Val = StringRef(A->getValue());
+    if (mips::hasCompactBranches(CPUName)) {
+      if (Val == "never" || Val == "always" || Val == "optimal") {
+        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;
+  }
 }
 
 /// getPPCTargetCPU - Get the (LLVM) name of the PowerPC cpu we are targeting.
 static std::string getPPCTargetCPU(const ArgList &Args) {
   if (Arg *A = Args.getLastArg(options::OPT_mcpu_EQ)) {
     StringRef CPUName = A->getValue();
 
     if (CPUName == "native") {
return (NanEncoding)llvm::StringSwitch<int>(CPU)
       .Case("mips64", NanLegacy)
       .Case("mips64r2", NanLegacy | Nan2008)
       .Case("mips64r3", NanLegacy | Nan2008)
       .Case("mips64r5", NanLegacy | Nan2008)
       .Case("mips64r6", Nan2008)
       .Default(NanLegacy);
 }
 
+bool mips::hasCompactBranches(StringRef &CPU) {
+  // mips32r6 and mips64r6 have compact branches.
+  return llvm::StringSwitch<bool>(CPU)
+      .Case("mips32r6", true)
+      .Case("mips64r6", true)
+      .Default(false);
+}
+
 bool mips::hasMipsAbiArg(const ArgList &Args, const char *Value) {
   Arg *A = Args.getLastArg(options::OPT_mabi_EQ);
   return A && (A->getValue() == StringRef(Value));
 }
 
 bool mips::isUCLibc(const ArgList &Args) {
   Arg *A = Args.getLastArg(options::OPT_m_libc_Group);
   return A && A->getOption().matches(options::OPT_muclibc);

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

 // CHECK-NAN2008: "-target-feature" "+nan2008"
 //
 // -mnan=legacy
 // RUN: %clang -target mips-linux-gnu -march=mips32r3 -### -c %s \
 // RUN:     -mnan=2008 -mnan=legacy 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NANLEGACY %s
 // CHECK-NANLEGACY: "-target-feature" "-nan2008"
 //
+// -mcompact-branches=never
+// RUN: %clang -target mips-linux-gnu -march=mips32r6 -### -c %s \
+// RUN:     -mcompact-branches=never 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-CBNEVER %s
+// CHECK-CBNEVER: "-mllvm" "-mips-compact-branches=never"
+//
+// -mcompact-branches=optimal
+// RUN: %clang -target mips-linux-gnu -march=mips32r6 -### -c %s \
+// RUN:     -mcompact-branches=optimal 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-CBOPTIMAL %s
+// CHECK-CBOPTIMAL: "-mllvm" "-mips-compact-branches=optimal"
+//
+// -mcompact-branches=always
+// RUN: %clang -target mips-linux-gnu -march=mips32r6 -### -c %s \
+// RUN:     -mcompact-branches=always 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-CBALWAYS %s
+// CHECK-CBALWAYS: "-mllvm" "-mips-compact-branches=always"
+//
 // -mxgot
 // RUN: %clang -target mips-linux-gnu -### -c %s \
 // RUN:     -mno-xgot -mxgot 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-XGOT %s
 // CHECK-XGOT: "-mllvm" "-mxgot"
 //
 // -mno-xgot
 // RUN: %clang -target mips-linux-gnu -### -c %s \