[clang][bytecode] Partially address string literal uniqueness (#142555)

This still leaves the case of the

constexpr auto b3 = name1() == name1();

test from cxx20.cpp broken.

1 files changed, 45 insertions, 0 deletions

diff --git a/clang/lib/AST/ByteCode/Interp.cpp b/clang/lib/AST/ByteCode/Interp.cpp
index 4d1e5c6..db91e5e 100644
--- a/clang/lib/AST/ByteCode/Interp.cpp
+++ b/clang/lib/AST/ByteCode/Interp.cpp
@@ -2008,6 +2008,51 @@ bool DiagTypeid(InterpState &S, CodePtr OpPC) {
   return false;
 }
 
+bool arePotentiallyOverlappingStringLiterals(const Pointer &LHS,
+                                             const Pointer &RHS) {
+  unsigned LHSOffset = LHS.getIndex();
+  unsigned RHSOffset = RHS.getIndex();
+  unsigned LHSLength = (LHS.getNumElems() - 1) * LHS.elemSize();
+  unsigned RHSLength = (RHS.getNumElems() - 1) * RHS.elemSize();
+
+  StringRef LHSStr((const char *)LHS.atIndex(0).getRawAddress(), LHSLength);
+  StringRef RHSStr((const char *)RHS.atIndex(0).getRawAddress(), RHSLength);
+  int32_t IndexDiff = RHSOffset - LHSOffset;
+  if (IndexDiff < 0) {
+    if (static_cast<int32_t>(LHSLength) < -IndexDiff)
+      return false;
+    LHSStr = LHSStr.drop_front(-IndexDiff);
+  } else {
+    if (static_cast<int32_t>(RHSLength) < IndexDiff)
+      return false;
+    RHSStr = RHSStr.drop_front(IndexDiff);
+  }
+
+  unsigned ShorterCharWidth;
+  StringRef Shorter;
+  StringRef Longer;
+  if (LHSLength < RHSLength) {
+    ShorterCharWidth = LHS.elemSize();
+    Shorter = LHSStr;
+    Longer = RHSStr;
+  } else {
+    ShorterCharWidth = RHS.elemSize();
+    Shorter = RHSStr;
+    Longer = LHSStr;
+  }
+
+  // The null terminator isn't included in the string data, so check for it
+  // manually. If the longer string doesn't have a null terminator where the
+  // shorter string ends, they aren't potentially overlapping.
+  for (unsigned NullByte : llvm::seq(ShorterCharWidth)) {
+    if (Shorter.size() + NullByte >= Longer.size())
+      break;
+    if (Longer[Shorter.size() + NullByte])
+      return false;
+  }
+  return Shorter == Longer.take_front(Shorter.size());
+}
+
 // https://github.com/llvm/llvm-project/issues/102513
 #if defined(_MSC_VER) && !defined(__clang__) && !defined(NDEBUG)
 #pragma optimize("", off)