Author: Craig Topper Date: 2025-08-09T09:23:04-05:00 New Revision: 92a966bd8f9fc5cd490ab956de202cd622cd7d32
URL: https://github.com/llvm/llvm-project/commit/92a966bd8f9fc5cd490ab956de202cd622cd7d32 DIFF: https://github.com/llvm/llvm-project/commit/92a966bd8f9fc5cd490ab956de202cd622cd7d32.diff LOG: [RISCV] Add -march=unset to cancel and ignore a previous -march. (#148321) -mcpu is used to determine the ISA string if an explicit -march is not present on the command line. If there is a -march present it always has priority over -mcpu regardless of where it appears in the command line. This can cause issues if -march appears in a Makefile and a user wants to override it with an -mcpu on the command line. The user would need to provide a potentially long ISA string to -march that matches the -mcpu in order to override the MakeFile. This issue can also be seen on Compiler Explorer where the rv64gc toolchain is passed -march=rv64gc before any user command line options are added. If you pass -mcpu=spacemit-x60, vectors will not be enabled due to the hidden -march. This patch adds a new option for -march, "unset" that makes the -march ignored for purposes of prioritizing over -mcpu. Now a user can write -march=unset -mcpu=<cpu_name>. This is also implemented by gcc for ARM32. An alternative would be to allow -march to take a cpu name, but that requires "-march=<cpu_name> -mcpu=<cpu_name>" or "-march=<cpu_name> -mtune=<cpu_name>" to ensure the tune cpu also gets updated. IMHO, needing to repeat the CPU name twice isn't friendly and invites mistakes. gcc has implemented this as well. Added: Modified: clang/docs/ReleaseNotes.rst clang/lib/Driver/ToolChains/Arch/RISCV.cpp clang/test/Driver/riscv-cpus.c Removed: ################################################################################ diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index 3462a099a5ebe..c6b0d32853da8 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -234,6 +234,9 @@ RISC-V Support - Add support for `__attribute__((interrupt("rnmi")))` to be used with the `Smrnmi` extension. With this the `Smrnmi` extension is fully supported. +- Add `-march=unset` to clear any previous `-march=` value. This ISA string will + be computed from `-mcpu` or the platform default. + CUDA/HIP Language Changes ^^^^^^^^^^^^^^^^^^^^^^^^^ diff --git a/clang/lib/Driver/ToolChains/Arch/RISCV.cpp b/clang/lib/Driver/ToolChains/Arch/RISCV.cpp index baa2c8c0bcfb2..76dde0da8e849 100644 --- a/clang/lib/Driver/ToolChains/Arch/RISCV.cpp +++ b/clang/lib/Driver/ToolChains/Arch/RISCV.cpp @@ -273,9 +273,12 @@ std::string riscv::getRISCVArch(const llvm::opt::ArgList &Args, // Clang does not yet support MULTILIB_REUSE, so we use `rv{XLEN}imafdc` // instead of `rv{XLEN}gc` though they are (currently) equivalent. - // 1. If `-march=` is specified, use it. - if (const Arg *A = Args.getLastArg(options::OPT_march_EQ)) - return A->getValue(); + // 1. If `-march=` is specified, use it unless the value is "unset". + if (const Arg *A = Args.getLastArg(options::OPT_march_EQ)) { + StringRef MArch = A->getValue(); + if (MArch != "unset") + return MArch.str(); + } // 2. Get march (isa string) based on `-mcpu=` if (const Arg *A = Args.getLastArg(options::OPT_mcpu_EQ)) { @@ -300,7 +303,7 @@ std::string riscv::getRISCVArch(const llvm::opt::ArgList &Args, StringRef MArch = llvm::RISCV::getMArchFromMcpu(CPU); // Bypass if target cpu's default march is empty. - if (MArch != "") + if (!MArch.empty()) return MArch.str(); } diff --git a/clang/test/Driver/riscv-cpus.c b/clang/test/Driver/riscv-cpus.c index 2698612f815d3..2a9c4e7021feb 100644 --- a/clang/test/Driver/riscv-cpus.c +++ b/clang/test/Driver/riscv-cpus.c @@ -403,6 +403,11 @@ // MCPU-MARCH: "-nostdsysteminc" "-target-cpu" "sifive-e31" "-target-feature" "+m" "-target-feature" "+c" // MCPU-MARCH: "-target-abi" "ilp32" +// -march=unset erases previous march +// RUN: %clang --target=riscv32 -### -c %s 2>&1 -march=rv32imc -march=unset -mcpu=sifive-e31 | FileCheck -check-prefix=MARCH-UNSET %s +// MARCH-UNSET: "-nostdsysteminc" "-target-cpu" "sifive-e31" "-target-feature" "+m" "-target-feature" "+a" "-target-feature" "+c" +// MARCH-UNSET-SAME: "-target-abi" "ilp32" + // Check interaction between -mcpu and mtune, -mtune won't affect arch related // target feature, but -mcpu will. // _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
