[llvm] [clang] [PowerPC][X86] Make cpu id builtins target independent and lower for PPC (PR #68919)

[via llvm-commits]

================
@@ -16086,6 +16086,41 @@ Value *CodeGenFunction::EmitPPCBuiltinExpr(unsigned BuiltinID,
   switch (BuiltinID) {
   default: return nullptr;
 
+  case Builtin::BI__builtin_cpu_is: {
+    const Expr *CPUExpr = E->getArg(0)->IgnoreParenCasts();
+    StringRef CPUStr = cast<clang::StringLiteral>(CPUExpr)->getString();
+    unsigned NumCPUID = StringSwitch<unsigned>(CPUStr)
+#define PPC_LNX_CPU(Name, NumericID) .Case(Name, NumericID)
+#include "llvm/TargetParser/PPCTargetParser.def"
+                            .Default(-1U);
+    Value *Op0 = llvm::ConstantInt::get(Int32Ty, PPC_FAWORD_CPUID);
+    llvm::Function *F = CGM.getIntrinsic(Intrinsic::ppc_fixed_addr_ld);
+    Value *TheCall = Builder.CreateCall(F, {Op0}, "cpu_is");
+    return Builder.CreateICmpEQ(TheCall,
+                                llvm::ConstantInt::get(Int32Ty, NumCPUID));
+  }
+  case Builtin::BI__builtin_cpu_supports: {
+    unsigned FeatureWord;
+    unsigned BitMask;
+    const Expr *CPUExpr = E->getArg(0)->IgnoreParenCasts();
+    StringRef CPUStr = cast<clang::StringLiteral>(CPUExpr)->getString();
+    std::tie(FeatureWord, BitMask) =
+        StringSwitch<std::pair<unsigned, unsigned>>(CPUStr)
+#define PPC_LNX_FEATURE(Name, Description, EnumName, Bitmask, FA_WORD)         \
+  .Case(Name, {FA_WORD, Bitmask})
+#include "llvm/TargetParser/PPCTargetParser.def"
+            .Default({0, 0});
----------------
diggerlin wrote:

 we do not want a default here,  without a default it will hit an assert here if fell off the end of the string-switch.
in the class of StringSwitch , there is function as 

```
  [[nodiscard]] operator R() {
    assert(Result && "Fell off the end of a string-switch");
    return std::move(*Result);
  }
```

https://github.com/llvm/llvm-project/pull/68919