[llvm-branch-commits] [AllocToken, Clang] Infer type hints from sizeof expressions and casts (PR #156841)

[Hans Wennborg via llvm-branch-commits]

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@@ -1353,6 +1354,92 @@ void CodeGenFunction::EmitAllocToken(llvm::CallBase *CB, QualType AllocType) {
   CB->setMetadata(llvm::LLVMContext::MD_alloc_token, MDN);
 }
 
+/// Infer type from a simple sizeof expression.
+static QualType inferTypeFromSizeofExpr(const Expr *E) {
+  const Expr *Arg = E->IgnoreParenImpCasts();
+  if (const auto *UET = dyn_cast<UnaryExprOrTypeTraitExpr>(Arg)) {
+    if (UET->getKind() == UETT_SizeOf) {
+      if (UET->isArgumentType())
+        return UET->getArgumentTypeInfo()->getType();
+      else
+        return UET->getArgumentExpr()->getType();
+    }
+  }
+  return QualType();
+}
+
+/// Infer type from an arithmetic expression involving a sizeof.
+static QualType inferTypeFromArithSizeofExpr(const Expr *E) {
+  const Expr *Arg = E->IgnoreParenImpCasts();
+  // The argument is a lone sizeof expression.
+  if (QualType T = inferTypeFromSizeofExpr(Arg); !T.isNull())
+    return T;
+  if (const auto *BO = dyn_cast<BinaryOperator>(Arg)) {
+    // Argument is an arithmetic expression. Cover common arithmetic patterns
+    // involving sizeof.
+    switch (BO->getOpcode()) {
+    case BO_Add:
+    case BO_Div:
+    case BO_Mul:
+    case BO_Shl:
+    case BO_Shr:
+    case BO_Sub:
+      if (QualType T = inferTypeFromArithSizeofExpr(BO->getLHS()); !T.isNull())
+        return T;
+      if (QualType T = inferTypeFromArithSizeofExpr(BO->getRHS()); !T.isNull())
+        return T;
+      break;
+    default:
+      break;
+    }
+  }
+  return QualType();
+}
+
+/// If the expression E is a reference to a variable, infer the type from a
+/// variable's initializer if it contains a sizeof. Beware, this is a heuristic
+/// and ignores if a variable is later reassigned.
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zmodem wrote:

nit: For readability, it would be nice if the comments contained a small example of the pattern that's being matched.

https://github.com/llvm/llvm-project/pull/156841