From 09bbc903a5b454d39d5ce69cf8bf6d5e1b46e3c4 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Timm=20B=C3=A4der?= <tbaeder@redhat.com>
Date: Fri, 14 Oct 2022 08:19:30 +0200
Subject: [PATCH] [clang][Interp] Array initialization via
 ImplicitValueInitExpr

Differential Revision: https://reviews.llvm.org/D135013
---
 clang/lib/AST/Interp/ByteCodeExprGen.cpp | 21 +++++++++++++++++++++
 clang/test/AST/Interp/arrays.cpp         | 12 ++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/clang/lib/AST/Interp/ByteCodeExprGen.cpp b/clang/lib/AST/Interp/ByteCodeExprGen.cpp
index ad3348c..872bbf0 100644
--- a/clang/lib/AST/Interp/ByteCodeExprGen.cpp
+++ b/clang/lib/AST/Interp/ByteCodeExprGen.cpp
@@ -722,6 +722,27 @@ bool ByteCodeExprGen<Emitter>::visitArrayInitializer(const Expr *Initializer) {
         return false;
     }
     return true;
+  } else if (const auto *IVIE = dyn_cast<ImplicitValueInitExpr>(Initializer)) {
+    const ArrayType *AT = IVIE->getType()->getAsArrayTypeUnsafe();
+    assert(AT);
+    const auto *CAT = cast<ConstantArrayType>(AT);
+    size_t NumElems = CAT->getSize().getZExtValue();
+
+    if (Optional<PrimType> ElemT = classify(CAT->getElementType())) {
+      // TODO(perf): For int and bool types, we can probably just skip this
+      //   since we memset our Block*s to 0 and so we have the desired value
+      //   without this.
+      for (size_t I = 0; I != NumElems; ++I) {
+        if (!this->emitZero(*ElemT, Initializer))
+          return false;
+        if (!this->emitInitElem(*ElemT, I, Initializer))
+          return false;
+      }
+    } else {
+      assert(false && "default initializer for non-primitive type");
+    }
+
+    return true;
   }
 
   assert(false && "Unknown expression for array initialization");
diff --git a/clang/test/AST/Interp/arrays.cpp b/clang/test/AST/Interp/arrays.cpp
index 318793f..d419994 100644
--- a/clang/test/AST/Interp/arrays.cpp
+++ b/clang/test/AST/Interp/arrays.cpp
@@ -117,3 +117,15 @@ namespace indices {
                                        // expected-error {{must be initialized by a constant expression}} \
                                        // expected-note {{cannot refer to element -2 of array of 10}}
 };
+
+namespace DefaultInit {
+  template <typename T, unsigned N>
+  struct B {
+    T a[N];
+  };
+
+  int f() {
+     constexpr B<int,10> arr = {};
+     constexpr int x = arr.a[0];
+  }
+};
-- 
2.7.4