[RISCV] Default enable RISCV linker relaxation

[shiva0217]

Summary

Default enable RISCV linker relaxation

[asb]

I think the backend part of this has seen plenty of testing and it would be worth merging this change. Thanks!

lib/Driver/ToolChains/Arch/RISCV.cpp

370

Personal preference that the LLVM coding style seems silent on, but I'll share anyway: I like omitting the braces for single-line blocks but find it a bit less readable in cases like this where the block's single statement spans multiple lines. I'd be tempted to add braces {}.

[asb]

Removing llvm-commits and adding cfe-commits. This patch is mistakenly marked as targeting the LLVM repo rather than Clang.

[shiva0217]

Update patch to address Alex's comment.

lib/Driver/ToolChains/Arch/RISCV.cpp

if (const Arg *A = Args.getLastArg(options::OPT_march_EQ)) {
     // Additional dependency checks.
     // TODO: The 'q' extension requires rv64.
     // TODO: It is illegal to specify 'e' extensions with 'f' and 'd'.
 
     // Handle all other types of extensions.
     getExtensionFeatures(D, Args, Features, MArch, OtherExts);
   }
 
+  // -mrelax is default, unless -mno-relax is specified.
+  bool Relax = true;
+  if (auto *A = Args.getLastArg(options::OPT_mrelax, options::OPT_mno_relax))
+    if (A->getOption().matches(options::OPT_mno_relax)) {
+      Relax = false;
+      Features.push_back("-relax");
+    }
+
+  if (Relax)
+    Features.push_back("+relax");
+
   // Now add any that the user explicitly requested on the command line,
   // which may override the defaults.
   handleTargetFeaturesGroup(Args, Features, options::OPT_m_riscv_Features_Group);
 }
 
 StringRef riscv::getRISCVABI(const ArgList &Args, const llvm::Triple &Triple) {
   if (Arg *A = Args.getLastArg(options::OPT_mabi_EQ))
     return A->getValue();
 
   return Triple.getArch() == llvm::Triple::riscv32 ? "ilp32" : "lp64";
 }

test/Driver/riscv-features.c

 // RUN: %clang -target riscv32-unknown-elf -### %s -fsyntax-only 2>&1 | FileCheck %s
 // RUN: %clang -target riscv64-unknown-elf -### %s -fsyntax-only 2>&1 | FileCheck %s
 
 // CHECK: fno-signed-char
 
 // RUN: %clang -target riscv32-unknown-elf -### %s -mrelax 2>&1 | FileCheck %s -check-prefix=RELAX
 // RUN: %clang -target riscv32-unknown-elf -### %s -mno-relax 2>&1 | FileCheck %s -check-prefix=NO-RELAX
+// RUN: %clang -target riscv32-unknown-elf -### %s 2>&1 | FileCheck %s -check-prefix=DEFAULT
 
 // RELAX: "-target-feature" "+relax"
 // NO-RELAX: "-target-feature" "-relax"
+// DEFAULT: "-target-feature" "+relax"