[clang] [CIR] Upstream CastOp and scalar conversions (PR #130690)

[Erich Keane via cfe-commits]

================
@@ -121,29 +359,159 @@ mlir::Value CIRGenFunction::emitScalarExpr(const Expr *e) {
   return ScalarExprEmitter(*this, builder).Visit(const_cast<Expr *>(e));
 }
 
+[[maybe_unused]] static bool MustVisitNullValue(const Expr *e) {
+  // If a null pointer expression's type is the C++0x nullptr_t, then
+  // it's not necessarily a simple constant and it must be evaluated
+  // for its potential side effects.
+  return e->getType()->isNullPtrType();
+}
+
 // Emit code for an explicit or implicit cast.  Implicit
 // casts have to handle a more broad range of conversions than explicit
 // casts, as they handle things like function to ptr-to-function decay
 // etc.
 mlir::Value ScalarExprEmitter::VisitCastExpr(CastExpr *ce) {
-  Expr *e = ce->getSubExpr();
+  Expr *subExpr = ce->getSubExpr();
   QualType destTy = ce->getType();
   CastKind kind = ce->getCastKind();
 
+  // These cases are generally not written to ignore the result of evaluating
+  // their sub-expressions, so we clear this now.
+  ignoreResultAssign = false;
+
   switch (kind) {
+  case clang::CK_Dependent:
+    llvm_unreachable("dependent cast kind in CIR gen!");
+  case clang::CK_BuiltinFnToFnPtr:
+    llvm_unreachable("builtin functions are handled elsewhere");
+
+  case CK_CPointerToObjCPointerCast:
+  case CK_BlockPointerToObjCPointerCast:
+  case CK_AnyPointerToBlockPointerCast:
+  case CK_BitCast: {
+    mlir::Value src = Visit(const_cast<Expr *>(subExpr));
+    mlir::Type dstTy = cgf.convertType(destTy);
+
+    assert(!cir::MissingFeatures::addressSpace());
+
+    if (cgf.sanOpts.has(SanitizerKind::CFIUnrelatedCast))
+      cgf.getCIRGenModule().errorNYI(subExpr->getSourceRange(),
+                                     "sanitizer support");
+
+    if (cgf.cgm.getCodeGenOpts().StrictVTablePointers)
+      cgf.getCIRGenModule().errorNYI(subExpr->getSourceRange(),
+                                     "strict vtable pointers");
+
+    // Update heapallocsite metadata when there is an explicit pointer cast.
+    assert(!cir::MissingFeatures::addHeapAllocSiteMetadata());
+
+    // If Src is a fixed vector and Dst is a scalable vector, and both have the
+    // same element type, use the llvm.vector.insert intrinsic to perform the
+    // bitcast.
+    assert(!cir::MissingFeatures::scalableVectors());
+
+    // If Src is a scalable vector and Dst is a fixed vector, and both have the
+    // same element type, use the llvm.vector.extract intrinsic to perform the
+    // bitcast.
+    assert(!cir::MissingFeatures::scalableVectors());
+
+    // Perform VLAT <-> VLST bitcast through memory.
+    // TODO: since the llvm.experimental.vector.{insert,extract} intrinsics
+    //       require the element types of the vectors to be the same, we
+    //       need to keep this around for bitcasts between VLAT <-> VLST where
+    //       the element types of the vectors are not the same, until we figure
+    //       out a better way of doing these casts.
+    assert(!cir::MissingFeatures::scalableVectors());
+
+    return cgf.getBuilder().createBitcast(cgf.getLoc(subExpr->getSourceRange()),
+                                          src, dstTy);
+  }
+
+  case CK_AtomicToNonAtomic:
+    cgf.getCIRGenModule().errorNYI(subExpr->getSourceRange(),
+                                   "CastExpr: ", ce->getCastKindName());
+    break;
----------------
erichkeane wrote:

what does this fall through to? Does it result in a sensible value?

https://github.com/llvm/llvm-project/pull/130690