95f0fab7fa
We used to create a scope for the true- and false expression of a
conditional operator. This was done so e.g. in this example:
```c++
struct A { constexpr A(){}; ~A(); constexpr int get() { return 10; } }; // all-note 2{{declared here}}
static_assert( (false ? A().get() : 1) == 1);
```
we did _not_ evaluate the true branch at all, meaning we did not
register the local variable for the temporary of type `A`, which means
we also didn't call it destructor.
However, this breaks the case where the temporary needs to outlive the
conditional operator and instead be destroyed via the surrounding
`ExprWithCleanups`:
```
constexpr bool test2(bool b) {
unsigned long __ms = b ? (const unsigned long &)0 : __ms;
return true;
}
static_assert(test2(true));
```
Before this patch, we diagnosed this example:
```console
./array.cpp:180:15: error: static assertion expression is not an integral constant expression
180 | static_assert(test2(true));
| ^~~~~~~~~~~
./array.cpp:177:24: note: read of temporary whose lifetime has ended
177 | unsigned long __ms = b ? (const unsigned long &)0 : __ms;
| ^
./array.cpp:180:15: note: in call to 'test2(true)'
180 | static_assert(test2(true));
| ^~~~~~~~~~~
./array.cpp:177:51: note: temporary created here
177 | unsigned long __ms = b ? (const unsigned long &)0 : __ms;
| ^
1 error generated.
```
because the temporary created for the true branch got immediately
destroyed.
The problem in essence is that since the conditional operator doesn't
create a scope at all, we register the local variables for both its
branches, but we later only execute one of them, which means we should
also only destroy the locals of one of the branches.
We fix this similar to clang codgen's `is_active` flag: In the case of a
conditional operator (which is so far the only case where this is
problematic, and this also helps minimize the performance impact of this
change), we make local variables as disabled-by-default and then emit a
`EnableLocal` opcode later, which marks them as enabled. The code
calling their destructors checks whether the local was enabled at all.
114 lines
3.4 KiB
C++
114 lines
3.4 KiB
C++
//===--- ByteCodeEmitter.h - Instruction emitter for the VM -----*- C++ -*-===//
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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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//
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// Defines the instruction emitters.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_CLANG_AST_INTERP_LINKEMITTER_H
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#define LLVM_CLANG_AST_INTERP_LINKEMITTER_H
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#include "Context.h"
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#include "PrimType.h"
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#include "Program.h"
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#include "Source.h"
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namespace clang {
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namespace interp {
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enum Opcode : uint32_t;
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/// An emitter which links the program to bytecode for later use.
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class ByteCodeEmitter {
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protected:
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using AddrTy = uintptr_t;
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using Local = Scope::Local;
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public:
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using LabelTy = uint32_t;
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/// Compiles the function into the module.
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void compileFunc(const FunctionDecl *FuncDecl, Function *Func = nullptr);
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protected:
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ByteCodeEmitter(Context &Ctx, Program &P) : Ctx(Ctx), P(P) {}
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virtual ~ByteCodeEmitter() {}
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/// Define a label.
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void emitLabel(LabelTy Label);
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/// Create a label.
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LabelTy getLabel() { return ++NextLabel; }
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/// Methods implemented by the compiler.
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virtual bool visitFunc(const FunctionDecl *E) = 0;
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virtual bool visitExpr(const Expr *E, bool DestroyToplevelScope) = 0;
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virtual bool visitDeclAndReturn(const VarDecl *VD, const Expr *Init,
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bool ConstantContext) = 0;
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virtual bool visit(const Expr *E) = 0;
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virtual bool emitBool(bool V, const Expr *E) = 0;
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/// Emits jumps.
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bool jumpTrue(const LabelTy &Label);
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bool jumpFalse(const LabelTy &Label);
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bool jump(const LabelTy &Label);
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bool fallthrough(const LabelTy &Label);
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/// Speculative execution.
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bool speculate(const CallExpr *E, const LabelTy &EndLabel);
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/// We're always emitting bytecode.
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bool isActive() const { return true; }
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bool checkingForUndefinedBehavior() const { return false; }
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/// Callback for local registration.
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Local createLocal(Descriptor *D);
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/// Parameter indices.
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llvm::DenseMap<const ParmVarDecl *, ParamOffset> Params;
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/// Lambda captures.
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llvm::DenseMap<const ValueDecl *, ParamOffset> LambdaCaptures;
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/// Offset of the This parameter in a lambda record.
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ParamOffset LambdaThisCapture{0, false};
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/// Local descriptors.
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llvm::SmallVector<SmallVector<Local, 8>, 2> Descriptors;
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std::optional<SourceInfo> LocOverride = std::nullopt;
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private:
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/// Current compilation context.
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Context &Ctx;
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/// Program to link to.
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Program &P;
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/// Index of the next available label.
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LabelTy NextLabel = 0;
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/// Offset of the next local variable.
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unsigned NextLocalOffset = 0;
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/// Label information for linker.
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llvm::DenseMap<LabelTy, unsigned> LabelOffsets;
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/// Location of label relocations.
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llvm::DenseMap<LabelTy, llvm::SmallVector<unsigned, 5>> LabelRelocs;
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/// Program code.
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llvm::SmallVector<std::byte> Code;
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/// Opcode to expression mapping.
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SourceMap SrcMap;
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/// Returns the offset for a jump or records a relocation.
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int32_t getOffset(LabelTy Label);
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/// Emits an opcode.
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template <typename... Tys>
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bool emitOp(Opcode Op, const Tys &...Args, SourceInfo L);
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protected:
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#define GET_LINK_PROTO
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#include "Opcodes.inc"
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#undef GET_LINK_PROTO
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};
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} // namespace interp
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} // namespace clang
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#endif
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