[clang-tools-extra] [clang-tidy] Add `modernize-use-bit-cast` check (PR #189962)

[Julian Schmidt via cfe-commits]

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@@ -0,0 +1,291 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "UseBitCastCheck.h"
+#include "../utils/Matchers.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/Expr.h"
+#include "clang/AST/ExprCXX.h"
+#include "clang/AST/Type.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Lexer.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/Twine.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::modernize {
+
+static bool isSupportedMemcpyObjectExpr(const Expr *ExprNode) {
+  ExprNode = ExprNode->IgnoreParenImpCasts();
+
+  if (isa<DeclRefExpr>(ExprNode))
+    return true;
+
+  const auto *Member = dyn_cast<MemberExpr>(ExprNode);
+  if (!Member || !isa<FieldDecl>(Member->getMemberDecl()))
+    if (const auto *MemberPointer = dyn_cast<BinaryOperator>(ExprNode))
+      if (MemberPointer->getOpcode() == BO_PtrMemD ||
+          MemberPointer->getOpcode() == BO_PtrMemI)
+        return isSupportedMemcpyObjectExpr(MemberPointer->getLHS());
+
+  return Member && isSupportedMemcpyObjectExpr(Member->getBase());
+}
+
+static const Expr *extractMemcpyObjectExpr(const Expr *ExprNode) {
+  ExprNode = ExprNode->IgnoreParenCasts();
+  const auto *AddressOf = dyn_cast<UnaryOperator>(ExprNode);
+  if (!AddressOf || AddressOf->getOpcode() != UO_AddrOf)
+    return nullptr;
+
+  const Expr *ObjectExpr = AddressOf->getSubExpr()->IgnoreParenImpCasts();
+  return isSupportedMemcpyObjectExpr(ObjectExpr) ? ObjectExpr : nullptr;
+}
+
+static bool isBitCastableMemcpyObjectType(QualType Type,
+                                          const ASTContext &Context) {
+  Type = Type.getCanonicalType().getNonReferenceType();
+  return !Type.isNull() && !Type.isVolatileQualified() &&
+         !Type->isAnyPointerType() && !Type->isFunctionType() &&
+         Type.isTriviallyCopyableType(Context) &&
+         Type.isBitwiseCloneableType(Context);
+}
+
+static bool canAssignBitCastResult(QualType Type) {
+  Type = Type.getCanonicalType().getNonReferenceType();
+  if (Type.isNull() || Type.isConstQualified() || Type->isArrayType())
+    return false;
+
+  const auto *Record = Type->getAsCXXRecordDecl();
+  return !Record || Record->hasSimpleCopyAssignment() ||
+         Record->hasSimpleMoveAssignment();
+}
+
+static bool isSameUnqualifiedCanonicalType(QualType LHS, QualType RHS) {
+  return LHS.getCanonicalType().getUnqualifiedType() ==
+         RHS.getCanonicalType().getUnqualifiedType();
+}
+
+static bool isMatchingSizeOfExpression(const Expr *SizeExpr, QualType SrcType,
+                                       QualType DstType,
+                                       const ASTContext &Context) {
+  const auto *UnaryExpr =
+      dyn_cast<UnaryExprOrTypeTraitExpr>(SizeExpr->IgnoreParenImpCasts());
+  if (!UnaryExpr || UnaryExpr->getKind() != UETT_SizeOf ||
+      SizeExpr->getBeginLoc().isMacroID())
+    return false;
+
+  const QualType SizeType = UnaryExpr->getTypeOfArgument();
+  if (SizeType.isNull())
+    return false;
+
+  const QualType SizeCanonical =
+      SizeType.getCanonicalType().getUnqualifiedType();
+  const QualType SrcCanonical = SrcType.getCanonicalType().getUnqualifiedType();
+  const QualType DstCanonical = DstType.getCanonicalType().getUnqualifiedType();
+  if (SizeCanonical != SrcCanonical && SizeCanonical != DstCanonical)
+    return false;
+
+  return Context.getTypeSizeInChars(SrcCanonical) ==
+         Context.getTypeSizeInChars(DstCanonical);
+}
+
+static bool isStatementBody(const Stmt *Current, const Stmt *Parent) {
+  if (const auto *Block = dyn_cast<CompoundStmt>(Parent))
+    return llvm::is_contained(Block->body(), Current);
+
+  if (const auto *If = dyn_cast<IfStmt>(Parent))
+    return If->getThen() == Current || If->getElse() == Current;
+  if (const auto *While = dyn_cast<WhileStmt>(Parent))
+    return While->getBody() == Current;
+  if (const auto *Do = dyn_cast<DoStmt>(Parent))
+    return Do->getBody() == Current;
+  if (const auto *For = dyn_cast<ForStmt>(Parent))
+    return For->getBody() == Current;
+  if (const auto *RangeFor = dyn_cast<CXXForRangeStmt>(Parent))
+    return RangeFor->getBody() == Current;
+  if (const auto *Label = dyn_cast<LabelStmt>(Parent))
+    return Label->getSubStmt() == Current;
+  if (const auto *Case = dyn_cast<SwitchCase>(Parent))
+    return Case->getSubStmt() == Current;
+  if (const auto *Attributed = dyn_cast<AttributedStmt>(Parent))
+    return Attributed->getSubStmt() == Current;
+
+  return false;
+}
+
+namespace {
+
+// These states describe how to spell the replacement when only the memcpy call
+// is replaced. An existing `(void)` cast is preserved by parenthesizing the
+// assignment, while comma/discarded subexpressions need an injected `(void)`.
+enum class MemcpyReplacementForm {
+  None,
+  StatementBody,
+  PreserveOuterVoidCast,
+  InjectVoidCast,
+};
+
+} // namespace
+
+static MemcpyReplacementForm getMemcpyReplacementForm(const Expr *ExprNode,
----------------
5chmidti wrote:

If the check now removes the void cast, the traversal up to the void cast should become a matcher with hasAncestor. I would've suggested this here as well via `optional` and binding the comma or cast ops.

https://github.com/llvm/llvm-project/pull/189962