[Multilib] Add -fmultilib-flag command-line option

[vhscampos]

This patch is the second step to extend the current multilib system to support the selection of library variants which do not correspond to existing command-line options.

Proposal can be found in https://discourse.llvm.org/t/rfc-multilib-custom-flags/81058

The multilib mechanism supports libraries that target code generation or language options such as --target, -mcpu, -mfpu, -mbranch-protection. However, some library variants are particular to features that do not correspond to any command-line options. Examples include variants for multithreading and semihosting.

This work introduces a way to instruct the multilib system to consider these features in library selection.

The driver must be informed about the multilib custom flags with a new command-line option.

-fmultilib-flag=C

Where the grammar for C is:

C -> option
option -> multithreaded | no-multithreaded | io-none | io-semihosting | io-linux-syscalls | ...

There must be one option instance for each flag specified:

-fmultilib-flag=multithreaded -fmultilib-flag=io-semihosting

Contradictory options are untied by last one wins.

These options are to be used exclusively by the multilib mechanism in the Clang driver. Hence they are not forwarded to the compiler frontend. On the other hand,

[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-driver

Author: Victor Campos (vhscampos)

Changes

This option is passed through to the multilib system. It is then used in conjunction with other options to select the proper library variant.

Details about this change can be found in this thread: https://discourse.llvm.org/t/rfc-multilib-custom-flags/81058

---

Full diff: https://github.com/llvm/llvm-project/pull/110658.diff

3 Files Affected:

• (modified) clang/include/clang/Driver/Options.td (+2)
• (modified) clang/lib/Driver/ToolChain.cpp (+14)
• (modified) clang/test/Driver/print-multi-selection-flags.c (+7)

diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 0cb7c0c0ae04f7..1fff1fa3edd052 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -5684,6 +5684,8 @@ def print_multi_directory : Flag<["-", "--"], "print-multi-directory">;
 def print_multi_lib : Flag<["-", "--"], "print-multi-lib">;
 def print_multi_flags : Flag<["-", "--"], "print-multi-flags-experimental">,
   HelpText<"Print the flags used for selecting multilibs (experimental)">;
+def fmultilib_flag : Joined<["-", "--"], "fmultilib-flag=">,
+  Visibility<[ClangOption]>;
 def print_multi_os_directory : Flag<["-", "--"], "print-multi-os-directory">,
   Flags<[Unsupported]>;
 def print_target_triple : Flag<["-", "--"], "print-target-triple">,
diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
index 4df31770950858..19f5f59897eda2 100644
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -196,6 +196,16 @@ bool ToolChain::defaultToIEEELongDouble() const {
   return PPC_LINUX_DEFAULT_IEEELONGDOUBLE && getTriple().isOSLinux();
 }
 
+static void
+processARMAArch64MultilibCustomFlags(Multilib::flags_list &List,
+                                     const llvm::opt::ArgList &Args) {
+  for (const Arg *MultilibFlagArg :
+       Args.filtered(options::OPT_fmultilib_flag)) {
+    List.push_back(MultilibFlagArg->getAsString(Args));
+    MultilibFlagArg->claim();
+  }
+}
+
 static void getAArch64MultilibFlags(const Driver &D,
                                           const llvm::Triple &Triple,
                                           const llvm::opt::ArgList &Args,
@@ -232,6 +242,8 @@ static void getAArch64MultilibFlags(const Driver &D,
   if (ABIArg) {
     Result.push_back(ABIArg->getAsString(Args));
   }
+
+  processARMAArch64MultilibCustomFlags(Result, Args);
 }
 
 static void getARMMultilibFlags(const Driver &D,
@@ -285,6 +297,8 @@ static void getARMMultilibFlags(const Driver &D,
   if (BranchProtectionArg) {
     Result.push_back(BranchProtectionArg->getAsString(Args));
   }
+
+  processARMAArch64MultilibCustomFlags(Result, Args);
 }
 
 static void getRISCVMultilibFlags(const Driver &D, const llvm::Triple &Triple,
diff --git a/clang/test/Driver/print-multi-selection-flags.c b/clang/test/Driver/print-multi-selection-flags.c
index 4bb62665ad8981..6bf50cd0976a6b 100644
--- a/clang/test/Driver/print-multi-selection-flags.c
+++ b/clang/test/Driver/print-multi-selection-flags.c
@@ -82,3 +82,10 @@
 // CHECK-RV32E-ORDER: --target=riscv32-unknown-none-elf
 // CHECK-RV32E-ORDER: -mabi=ilp32e
 // CHECK-RV32E-ORDER: -march=rv32e{{[0-9]+p[0-9]+}}_c{{[0-9]+p[0-9]+}}_zicsr{{[0-9]+p[0-9]+}}
+
+// RUN: %clang -print-multi-flags-experimental --target=armv8m.main-none-eabi -fmultilib-flag=foo -fmultilib-flag=bar | FileCheck --check-prefixes=CHECK-MULTILIB-CUSTOM-FLAG,CHECK-ARM-MULTILIB-CUSTOM-FLAG %s
+// RUN: %clang -print-multi-flags-experimental --target=aarch64-none-eabi     -fmultilib-flag=foo -fmultilib-flag=bar | FileCheck --check-prefixes=CHECK-MULTILIB-CUSTOM-FLAG,CHECK-AARCH64-MULTILIB-CUSTOM-FLAG %s
+// CHECK-ARM-MULTILIB-CUSTOM-FLAG:     --target=thumbv8m.main-unknown-none-eabi
+// CHECK-AARCH64-MULTILIB-CUSTOM-FLAG: --target=aarch64-unknown-none-eabi
+// CHECK-MULTILIB-CUSTOM-FLAG-DAG:     -fmultilib-flag=foo
+// CHECK-MULTILIB-CUSTOM-FLAG-DAG:     -fmultilib-flag=bar