[CIR] Make the asserts to display suggestion for -fno-clangir-call-conv-lowering

While here, add more unrecheables to cover some of the current errors, so that
our users can see a clear message instead of a random cast assert of sorts.
This covers at least all crashes seen when removing
-fno-clangir-call-conv-lowering from all tests, there are probably other things
we'll find as we exercise this path.

Author: bcardosolopes

clang/include/clang/CIR/MissingFeatures.h

@@ -15,6 +15,8 @@
 #ifndef CLANG_CIR_MISSINGFEATURES_H
 #define CLANG_CIR_MISSINGFEATURES_H
 
+#include <llvm/Support/raw_ostream.h>
+
 constexpr bool cirMissingFeatureAssertionMode =
     true; // Change to `false` to use llvm_unreachable
 
@@ -24,9 +26,15 @@ constexpr bool cirMissingFeatureAssertionMode =
   " point."
 
 // Special assertion to be used in the target lowering library.
-#define cir_tl_assert(cond) assert((cond) && NOTE);
+#define cir_tl_assert(cond)                                                    \
+  do {                                                                         \
+    if (!(cond))                                                               \
+      llvm::errs() << NOTE << "\n";                                            \
+    assert((cond));                                                            \
+  } while (0)
 
-// Special
+// Special version of cir_unreachable to give more info to the user on how
+// to temporaruly disable target lowering.
 #define cir_unreachable(msg)                                                   \
   do {                                                                         \
     llvm_unreachable(msg NOTE);                                                \

clang/lib/CIR/Dialect/Transforms/CallConvLowering.cpp

@@ -51,7 +51,9 @@ struct CallConvLoweringPattern : public OpRewritePattern<FuncOp> {
           continue;
         }
 
-        auto callOp = cast<CallOp>(call.getUser());
+        auto callOp = dyn_cast_or_null<CallOp>(call.getUser());
+        if (!callOp)
+          cir_unreachable("NYI empty callOp");
         if (lowerModule->rewriteFunctionCall(callOp, op).failed())
           return failure();
       }

clang/lib/CIR/Dialect/Transforms/TargetLowering/LowerFunction.cpp

@@ -210,6 +210,9 @@ Value castReturnValue(Value Src, Type Ty, LowerFunction &LF) {
   if (isa<BoolType>(SrcTy) && isa<IntType>(Ty))
     return createBitcast(Src, Ty, LF);
 
+  auto intTy = dyn_cast<IntType>(Ty);
+  if (intTy && !intTy.isPrimitive())
+    cir_unreachable("non-primitive types NYI");
   llvm::TypeSize DstSize = LF.LM.getDataLayout().getTypeAllocSize(Ty);
 
   // FIXME(cir): Do we need the EnterStructPointerForCoercedAccess routine here?