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

[Craig Topper via cfe-commits]

================
@@ -2877,10 +2877,144 @@ 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");
+  }
+}
+
+static int getPrioiryFromAttrString(StringRef AttrStr) {
+  SmallVector<StringRef, 8> Attrs;
+
+  AttrStr.split(Attrs, ";");
+
+  // Default Pri is zero.
+  int Pri = 0;
+  for (auto Attr : Attrs) {
+    if (Attr.starts_with("priority=")) {
+      Attr.consume_front("priority=");
+      int Result;
+      if (!Attr.getAsInteger(0, Result)) {
+        Pri = Result;
+      }
+    }
+  }
+
+  return Pri;
+}
+
+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;
+
+  SmallVector<CodeGenFunction::MultiVersionResolverOption, 10> CurrOptions(
+      Options);
+
+  llvm::stable_sort(
+      CurrOptions, [](const CodeGenFunction::MultiVersionResolverOption &LHS,
+                      const CodeGenFunction::MultiVersionResolverOption &RHS) {
+        return getPrioiryFromAttrString(LHS.Conditions.Features[0]) >
+               getPrioiryFromAttrString(RHS.Conditions.Features[0]);
+      });
+
+  // Check the each candidate function.
+  for (unsigned Index = 0; Index < CurrOptions.size(); Index++) {
+
+    if (CurrOptions[Index].Conditions.Features[0].starts_with("default")) {
----------------
topperc wrote:

Can "default" have a priority? Can the priority appear before "default" in the features?

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