[clang] Support -fpic -fno-semantic-interposition for RISCV

[MaskRay]

Summary

-fno-semantic-interposition (only effective with -fpic) can optimize default
visibility external linkage (non-ifunc-non-COMDAT) variable access and function
calls to avoid GOT/PLT, by using local aliases, e.g.

int var;
__attribute__((optnone)) int fun(int x) { return x * x; }
int test() { return fun(var); }

-fpic (var and fun are dso_preemptable)

test:
.LBB1_1:
        auipc   a0, %got_pcrel_hi(var)
        ld      a0, %pcrel_lo(.LBB1_1)(a0)
        lw      a0, 0(a0)
// fun is preemptible by default in ld -shared mode. ld will create a PLT.
        tail    fun@plt

vs -fpic -fno-semantic-interposition (var and fun are dso_local)

test:
.Ltest$local:
.LBB1_1:
        auipc   a0, %pcrel_hi(.Lvar$local)
        addi    a0, a0, %pcrel_lo(.LBB1_1)
        lw      a0, 0(a0)
// The assembler either resolves .Lfun$local at assembly time (-mno-relax
// -fno-function-sections), or produces a relocation referencing a non-preemptible
// local symbol (which can avoid PLT).
        tail    .Lfun$local

Note: Clang's default -fpic is more aggressive than GCC -fpic: interprocedural
optimizations (including inlining) are available but local aliases are not used.
-fpic -fsemantic-interposition can disable interprocedural optimizations.

Depends on D101875

[luismarques]

LGTM.

[MaskRay]

rebase after aarch64 support

clang/lib/Driver/ToolChains/Clang.cpp

#endif
   // Otherwise use Clang's traditional behavior: like
   // -fno-semantic-interposition but local aliases are not used. So references
   // can be interposed if not optimized out.
   if (Triple.isOSBinFormatELF()) {
     Arg *A = Args.getLastArg(options::OPT_fsemantic_interposition,
                              options::OPT_fno_semantic_interposition);
     if (RelocationModel != llvm::Reloc::Static && !IsPIE) {
       // The supported targets need to call AsmPrinter::getSymbolPreferLocal.
-      bool SupportsLocalAlias = Triple.isAArch64() || Triple.isX86();
+      bool SupportsLocalAlias =
+          Triple.isAArch64() || Triple.isRISCV() || Triple.isX86();
       if (!A)
         CmdArgs.push_back("-fhalf-no-semantic-interposition");
       else if (A->getOption().matches(options::OPT_fsemantic_interposition))
         A->render(Args, CmdArgs);
       else if (!SupportsLocalAlias)
         CmdArgs.push_back("-fhalf-no-semantic-interposition");
     }
   }

clang/test/Driver/fsemantic-interposition.c

 // RUN: %clang -target x86_64 %s -Werror -fpic -fsemantic-interposition -c -### 2>&1 | FileCheck %s
 // RUN: %clang -target x86_64 %s -Werror -fPIC -fsemantic-interposition -c -### 2>&1 | FileCheck %s
 // CHECK: "-fsemantic-interposition"
 
 /// No-op for -fno-pic/-fpie.
 // RUN: %clang -target x86_64 %s -Werror -fsemantic-interposition -c -### 2>&1 | FileCheck --check-prefix=NOOP %s
 // RUN: %clang -target x86_64 %s -Werror -fPIE -fsemantic-interposition -c -### 2>&1 | FileCheck --check-prefix=NOOP %s
 // NOOP-NOT: "-fsemantic-interposition"
 // NOOP-NOT: "-fno-semantic-interposition"
 
 /// If -fno-semantic-interposition is specified and the target supports local
 /// aliases, neither CC1 option is set.
 // RUN: %clang -target aarch64 %s -Werror -fPIC -fno-semantic-interposition -c -### 2>&1 | FileCheck --check-prefix=NO %s
+// RUN: %clang -target riscv32 %s -Werror -fPIC -fno-semantic-interposition -c -### 2>&1 | FileCheck --check-prefix=NO %s
+// RUN: %clang -target riscv64 %s -Werror -fPIC -fno-semantic-interposition -c -### 2>&1 | FileCheck --check-prefix=NO %s
 // RUN: %clang -target i386 %s -Werror -fPIC -fno-semantic-interposition -c -### 2>&1 | FileCheck --check-prefix=NO %s
 // RUN: %clang -target x86_64 %s -Werror -fPIC -fno-semantic-interposition -c -### 2>&1 | FileCheck --check-prefix=NO %s
 // NO-NOT: "-fsemantic-interposition"
 // NO-NOT: "-fhalf-no-semantic-interposition"
 
 /// If neither -fsemantic-interposition or -fno-semantic-interposition is specified,
 /// or -fno-semantic-interposition is specified but the target does not support
 /// local aliases, use the traditional half-baked behavor: interprocedural
 /// optimizations are allowed but local aliases are not used. If references are
 /// not optimized out, semantic interposition at runtime is possible.
 // RUN: %clang -target ppc64le %s -Werror -fPIC -fno-semantic-interposition -c -### 2>&1 | FileCheck --check-prefix=HALF %s
-// RUN: %clang -target riscv64 %s -Werror -fPIC -fno-semantic-interposition -c -### 2>&1 | FileCheck --check-prefix=HALF %s
 
 // RUN: %clang -target x86_64 %s -Werror -fPIC -c -### 2>&1 | FileCheck --check-prefix=HALF %s
 //
 // HALF: "-fhalf-no-semantic-interposition"