[clang] [clang][bytecode] Consider start index when copying composite array (PR #121461)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

<details>
<summary>Changes</summary>

... elements.

---
Full diff: https://github.com/llvm/llvm-project/pull/121461.diff


2 Files Affected:

- (modified) clang/lib/AST/ByteCode/InterpBuiltinBitCast.cpp (+1-1) 
- (modified) clang/test/AST/ByteCode/builtin-functions.cpp (+10) 


``````````diff
diff --git a/clang/lib/AST/ByteCode/InterpBuiltinBitCast.cpp b/clang/lib/AST/ByteCode/InterpBuiltinBitCast.cpp
index 0fc94e1694822a..57c1fab5d6ab43 100644
--- a/clang/lib/AST/ByteCode/InterpBuiltinBitCast.cpp
+++ b/clang/lib/AST/ByteCode/InterpBuiltinBitCast.cpp
@@ -110,7 +110,7 @@ static bool enumerateData(const Pointer &P, const Context &Ctx, Bits Offset,
   if (FieldDesc->isCompositeArray()) {
     QualType ElemType = FieldDesc->getElemQualType();
     Bits ElemSize = Bits(Ctx.getASTContext().getTypeSize(ElemType));
-    for (unsigned I = 0; I != FieldDesc->getNumElems(); ++I) {
+    for (unsigned I = P.getIndex(); I != FieldDesc->getNumElems(); ++I) {
       enumerateData(P.atIndex(I).narrow(), Ctx, Offset, BitsToRead, F);
       Offset += ElemSize;
       if (Offset >= BitsToRead)
diff --git a/clang/test/AST/ByteCode/builtin-functions.cpp b/clang/test/AST/ByteCode/builtin-functions.cpp
index b0f8ea2e55ee0b..0188e8297db528 100644
--- a/clang/test/AST/ByteCode/builtin-functions.cpp
+++ b/clang/test/AST/ByteCode/builtin-functions.cpp
@@ -1253,6 +1253,16 @@ namespace BuiltinMemcpy {
   static_assert(test_memmove(2, 0, 12) == 4234); // both-error {{constant}} \
                                                  // both-note {{in call}}
 #endif
+
+  struct Trivial { char k; short s; constexpr bool ok() { return k == 3 && s == 4; } };
+  constexpr bool test_trivial() {
+    Trivial arr[3] = {{1, 2}, {3, 4}, {5, 6}};
+    __builtin_memcpy(arr, arr+1, sizeof(Trivial));
+    __builtin_memmove(arr+1, arr, 2 * sizeof(Trivial));
+
+    return arr[0].ok() && arr[1].ok() && arr[2].ok();
+  }
+  static_assert(test_trivial());
 }
 
 namespace Memcmp {

``````````

</details>


https://github.com/llvm/llvm-project/pull/121461