[clang] [llvm] [RISCV][FMV] Support target_clones (PR #85786)

[Philip Reames via cfe-commits]

================
@@ -2854,10 +2854,121 @@ void CodeGenFunction::EmitMultiVersionResolver(
   case llvm::Triple::aarch64:
     EmitAArch64MultiVersionResolver(Resolver, Options);
     return;
+  case llvm::Triple::riscv32:
+  case llvm::Triple::riscv64:
+    EmitRISCVMultiVersionResolver(Resolver, Options);
+    return;
 
   default:
-    assert(false && "Only implemented for x86 and AArch64 targets");
+    assert(false && "Only implemented for x86, AArch64 and RISC-V targets");
+  }
+}
+
+void CodeGenFunction::EmitRISCVMultiVersionResolver(
+    llvm::Function *Resolver, ArrayRef<MultiVersionResolverOption> Options) {
+
+  if (getContext().getTargetInfo().getTriple().getOS() !=
+      llvm::Triple::OSType::Linux) {
+    CGM.getDiags().Report(diag::err_os_unsupport_riscv_target_clones);
+    return;
+  }
+
+  llvm::BasicBlock *CurBlock = createBasicBlock("resolver_entry", Resolver);
+  Builder.SetInsertPoint(CurBlock);
+  EmitRISCVCpuInit();
+
+  bool SupportsIFunc = getContext().getTargetInfo().supportsIFunc();
+  bool HasDefault = false;
+  unsigned DefaultIndex = 0;
+  // Check the each candidate function.
+  for (unsigned Index = 0; Index < Options.size(); Index++) {
----------------
preames wrote:

There's a semantic problem here unless I'm missing something.   Say the user specifies three choices: default, zba, and zba+zbb (in that order.)  Unless I'm missing something, the third case would be dead here which is almost certainly not what the user intended.  How do other targets handle this case?

https://github.com/llvm/llvm-project/pull/85786