e511026bf0
Diagnostic stores various notes/error messages which might help the user in debugging. For the most part, the `Diagnostic` when receiving an error message will copy and own the contents of the string. However, there is one optimization where given a `const char*`, the class will assume this is a StringLiteral which is immutable and lifetime matches that of the entire program. As a result, instead of copying the message in these cases the class will simply store the underlying pointer. This is problematic since `const char*` is not specific enough to always imply a StringLiteral which can lead to bugs, e.g. if the underlying pointer is freed before the diagnostic reports. We solve this problem by choosing a more specific function signature. While not full-proof, this should cover a lot more cases. A potentially better alternative is just deleting this special handling of string literals, but I am unsure of the implications (it does sound safe to do however with a negligble impact on performance).
64 lines
2.1 KiB
C++
64 lines
2.1 KiB
C++
//===- Diagnostic.cpp - Dialect unit tests -------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "mlir/IR/Diagnostics.h"
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#include "mlir/Support/TypeID.h"
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#include "gtest/gtest.h"
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using namespace mlir;
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using namespace mlir::detail;
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namespace {
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TEST(DiagnosticLifetime, TestCopiesConstCharStar) {
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const auto *expectedMessage = "Error 1, don't mutate this";
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// Copy expected message into a mutable container, and call the constructor.
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std::string myStr(expectedMessage);
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mlir::MLIRContext context;
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Diagnostic diagnostic(mlir::UnknownLoc::get(&context),
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DiagnosticSeverity::Note);
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diagnostic << myStr.c_str();
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// Mutate underlying pointer, but ensure diagnostic still has orig. message
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myStr[0] = '^';
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std::string resultMessage;
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llvm::raw_string_ostream stringStream(resultMessage);
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diagnostic.print(stringStream);
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ASSERT_STREQ(expectedMessage, resultMessage.c_str());
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}
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TEST(DiagnosticLifetime, TestLazyCopyStringLiteral) {
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char charArr[21] = "Error 1, mutate this";
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mlir::MLIRContext context;
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Diagnostic diagnostic(mlir::UnknownLoc::get(&context),
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DiagnosticSeverity::Note);
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// Diagnostic contains optimization which assumes string literals are
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// represented by `const char[]` type. This is imperfect as we can sometimes
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// trick the type system as seen below.
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//
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// Still we use this to check the diagnostic is lazily storing the pointer.
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auto addToDiagnosticAsConst = [&diagnostic](const char(&charArr)[21]) {
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diagnostic << charArr;
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};
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addToDiagnosticAsConst(charArr);
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// Mutate the underlying pointer and ensure the string does change
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charArr[0] = '^';
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std::string resultMessage;
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llvm::raw_string_ostream stringStream(resultMessage);
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diagnostic.print(stringStream);
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ASSERT_STREQ("^rror 1, mutate this", resultMessage.c_str());
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}
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} // namespace
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