[clang] [CIR] Handle FunctionToPointerDecay casts (#153657) (PR #154060)

[Morris Hafner via cfe-commits]

================
@@ -73,21 +73,59 @@ Address CIRGenFunction::emitPointerWithAlignment(const Expr *expr,
 
   // Casts:
   if (auto const *ce = dyn_cast<CastExpr>(expr)) {
-    if (isa<ExplicitCastExpr>(ce)) {
-      cgm.errorNYI(expr->getSourceRange(),
-                   "emitPointerWithAlignment: explicit cast");
-      return Address::invalid();
-    }
+    if (const auto *ece = dyn_cast<ExplicitCastExpr>(ce))
+      cgm.emitExplicitCastExprType(ece);
 
     switch (ce->getCastKind()) {
     // Non-converting casts (but not C's implicit conversion from void*).
     case CK_BitCast:
     case CK_NoOp:
     case CK_AddressSpaceConversion: {
-      cgm.errorNYI(expr->getSourceRange(),
-                   "emitPointerWithAlignment: noop cast");
-      return Address::invalid();
-    } break;
+      if (const auto *ptrTy =
+              ce->getSubExpr()->getType()->getAs<PointerType>()) {
+        if (ptrTy->getPointeeType()->isVoidType())
+          break;
+
+        LValueBaseInfo innerBaseInfo;
+        Address addr =
+            emitPointerWithAlignment(ce->getSubExpr(), &innerBaseInfo);
+        if (baseInfo)
+          *baseInfo = innerBaseInfo;
+
+        if (isa<ExplicitCastExpr>(ce)) {
+          LValueBaseInfo targetTypeBaseInfo;
+
+          const QualType pointeeType = expr->getType()->getPointeeType();
+          const CharUnits align =
+              cgm.getNaturalTypeAlignment(pointeeType, &targetTypeBaseInfo);
+
+          // If the source l-value is opaque, honor the alignment of the
+          // casted-to type.
+          if (innerBaseInfo.getAlignmentSource() != AlignmentSource::Decl) {
+            if (baseInfo)
+              baseInfo->mergeForCast(targetTypeBaseInfo);
+            addr = Address(addr.getPointer(), addr.getElementType(), align);
+          }
+        }
+
+        if (sanOpts.has(SanitizerKind::CFIUnrelatedCast) &&
+            ce->getCastKind() == CK_BitCast) {
+          if (expr->getType()->getAs<PointerType>())
+            llvm_unreachable("NYI");
+        }
+
+        const auto eltTy = convertTypeForMem(expr->getType()->getPointeeType());
+        addr = getBuilder().createElementBitCast(getLoc(expr->getSourceRange()),
+                                                 addr, eltTy);
+        if (ce->getCastKind() == CK_AddressSpaceConversion) {
+          assert(!cir::MissingFeatures::addressSpace());
+          llvm_unreachable("NYI");
+        }
----------------
mmha wrote:

```suggestion
        assert(ce->getCastKind() != CK_AddressSpaceConversion && !cir::MissingFeatures::addressSpace());
```

https://github.com/llvm/llvm-project/pull/154060