[clang] [llvm] LLVM] Add `__builtin_readfixedtimer` intrinsic and buiiltin for realtime clocks (PR #81331)

[Joseph Huber via cfe-commits]

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@@ -312,6 +312,12 @@ void IntrinsicLowering::LowerIntrinsicCall(CallInst *CI) {
     CI->replaceAllUsesWith(ConstantInt::get(Type::getInt64Ty(Context), 0));
     break;
   }
+  case Intrinsic::readfixedtimer: {
+    errs() << "WARNING: this target does not support the llvm.readfixedtimer"
+           << " intrinsic.  It is being lowered to a constant 0\n";
+    CI->replaceAllUsesWith(ConstantInt::get(Type::getInt64Ty(Context), 0));
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jhuber6 wrote:

I copied it from the other one, but either way works. I think setting it to zero is a little more explicit.

https://github.com/llvm/llvm-project/pull/81331