[embedded] Fix IR verification crash when using arrays of zero-sized structs

Author: kubamracek

lib/IRGen/GenBuiltin.cpp

@@ -1115,6 +1115,10 @@ void irgen::emitBuiltinCall(IRGenFunction &IGF, const BuiltinInfo &Builtin,
       SILType elemTy = valueTy.first;
       const TypeInfo &elemTI = valueTy.second;
 
+      if (elemTI.isTriviallyDestroyable(ResilienceExpansion::Maximal) ==
+          IsTriviallyDestroyable)
+        return;
+
       llvm::Value *firstElem = IGF.Builder.CreateBitCast(
           ptr, elemTI.getStorageType()->getPointerTo());
 
@@ -1175,6 +1179,15 @@ void irgen::emitBuiltinCall(IRGenFunction &IGF, const BuiltinInfo &Builtin,
       SILType elemTy = tyPair.first;
       const TypeInfo &elemTI = tyPair.second;
 
+      // Do nothing for zero-sized POD array elements.
+      if (llvm::Constant *SizeConst = elemTI.getStaticSize(IGF.IGM)) {
+        auto *SizeInt = cast<llvm::ConstantInt>(SizeConst);
+        if (SizeInt->getSExtValue() == 0 &&
+            elemTI.isTriviallyDestroyable(ResilienceExpansion::Maximal) ==
+                IsTriviallyDestroyable)
+          return;
+      }
+
       llvm::Value *firstSrcElem = IGF.Builder.CreateBitCast(
           src, elemTI.getStorageType()->getPointerTo());
       llvm::Value *firstDestElem = IGF.Builder.CreateBitCast(

test/embedded/array-zero-size-struct.swift

@@ -0,0 +1,21 @@
+// RUN: %target-swift-frontend -emit-ir %s -enable-experimental-feature Embedded | %FileCheck %s
+
+// REQUIRES: VENDOR=apple
+// REQUIRES: OS=macosx
+
+public struct MyStruct {
+}
+
+public func main() {
+  var arr: [MyStruct] = []
+  var arr2: [MyStruct] = [.init()]
+  var arr3 = arr2
+  arr3.append(MyStruct())
+}
+
+public func copy(_ a: inout [MyStruct]) {
+  var a = a
+}
+
+// CHECK: define {{.*}}@"$s4mainAAyyF"
+// CHECK: define {{.*}}@"$s4main4copyyySayAA8MyStructVGzF"