[RISCV] Set triple based on -march flag

For RISC-V the value provided to -march should determine whether to
compile for 32- or 64-bit RISC-V irrespective of the target provided to
the Clang driver. This adds a test for this flag for RISC-V and sets the
Target architecture correctly in these cases.

Differential Revision: https://reviews.llvm.org/D54214

clang/docs/ReleaseNotes.rst

@@ -112,7 +112,8 @@ future versions of Clang.
 Modified Compiler Flags
 -----------------------
 
-- ...
+- RISC-V now sets the architecture (riscv32/riscv64) based on the value provided
+  to the ``-march`` flag, overriding the target provided by ``-triple``.
 
 New Pragmas in Clang
 --------------------

clang/lib/Driver/Driver.cpp

@@ -541,6 +541,17 @@ static llvm::Triple computeTargetTriple(const Driver &D,
     }
   }
 
+  // If target is RISC-V adjust the target triple according to
+  // provided architecture name
+  A = Args.getLastArg(options::OPT_march_EQ);
+  if (A && Target.isRISCV()) {
+    StringRef ArchName = A->getValue();
+    if (ArchName.startswith_lower("rv32"))
+      Target.setArch(llvm::Triple::riscv32);
+    else if (ArchName.startswith_lower("rv64"))
+      Target.setArch(llvm::Triple::riscv64);
+  }
+
   return Target;
 }
 

clang/test/Driver/riscv-arch.c

@@ -315,3 +315,15 @@
 // RUN: -fsyntax-only 2>&1 | FileCheck -check-prefix=RV32-X-S-SX-INVAL %s
 // RV32-X-S-SX-INVAL: error: invalid arch name 'rv32ixabc_sdef_sxghi',
 // RV32-X-S-SX-INVAL: unsupported non-standard user-level extension 'xabc'
+
+// RUN: %clang -target riscv32-unknown-elf -march=rv32i -### %s \
+// RUN: -fsyntax-only 2>&1 | FileCheck -check-prefix=RV32-TARGET %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv32i -### %s \
+// RUN: -fsyntax-only 2>&1 | FileCheck -check-prefix=RV32-TARGET %s
+// RV32-TARGET: "-triple" "riscv32-unknown-unknown-elf"
+
+// RUN: %clang -target riscv32-unknown-elf -march=rv64i -### %s \
+// RUN: -fsyntax-only 2>&1 | FileCheck -check-prefix=RV64-TARGET %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv64i -### %s \
+// RUN: -fsyntax-only 2>&1 | FileCheck -check-prefix=RV64-TARGET %s
+// RV64-TARGET: "-triple" "riscv64-unknown-unknown-elf"