Timm =?utf-8?q?Bäder?= <tbae...@redhat.com>, Timm =?utf-8?q?Bäder?= <tbae...@redhat.com>, Timm =?utf-8?q?Bäder?= <tbae...@redhat.com>, Timm =?utf-8?q?Bäder?= <tbae...@redhat.com>, Timm =?utf-8?q?Bäder?= <tbae...@redhat.com>, Timm =?utf-8?q?Bäder?= <tbae...@redhat.com>, Timm =?utf-8?q?Bäder?= <tbae...@redhat.com>, Timm =?utf-8?q?Bäder?= <tbae...@redhat.com>, Timm =?utf-8?q?Bäder?= <tbae...@redhat.com>, Timm =?utf-8?q?Bäder?= <tbae...@redhat.com>, Timm =?utf-8?q?Bäder?= <tbae...@redhat.com>, Timm =?utf-8?q?Bäder?= <tbae...@redhat.com>, Timm =?utf-8?q?Bäder?= <tbae...@redhat.com> Message-ID: In-Reply-To: <llvm.org/llvm/llvm-project/pull/68...@github.com>
================ @@ -0,0 +1,452 @@ +//===--- InterpBitcast.cpp - Interpreter for the constexpr VM ---*- C++ -*-===// +// +// 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 "Boolean.h" +#include "Interp.h" +#include "PrimType.h" +#include "clang/AST/ASTContext.h" +#include "clang/AST/RecordLayout.h" +#include "clang/Basic/Builtins.h" +#include "clang/Basic/TargetInfo.h" +#include "llvm/ADT/BitVector.h" + +namespace clang { +namespace interp { + +/// Used to iterate over pointer fields. +using DataFunc = + llvm::function_ref<bool(const Pointer &P, PrimType Ty, size_t BitOffset)>; + +#define BITCAST_TYPE_SWITCH(Expr, B) \ + do { \ + switch (Expr) { \ + TYPE_SWITCH_CASE(PT_Sint8, B) \ + TYPE_SWITCH_CASE(PT_Uint8, B) \ + TYPE_SWITCH_CASE(PT_Sint16, B) \ + TYPE_SWITCH_CASE(PT_Uint16, B) \ + TYPE_SWITCH_CASE(PT_Sint32, B) \ + TYPE_SWITCH_CASE(PT_Uint32, B) \ + TYPE_SWITCH_CASE(PT_Sint64, B) \ + TYPE_SWITCH_CASE(PT_Uint64, B) \ + TYPE_SWITCH_CASE(PT_IntAP, B) \ + TYPE_SWITCH_CASE(PT_IntAPS, B) \ + TYPE_SWITCH_CASE(PT_Bool, B) \ + default: \ + llvm_unreachable("Unhandled bitcast type"); \ + } \ + } while (0) + +/// Float is a special case that sometimes needs the floating point semantics +/// to be available. +#define BITCAST_TYPE_SWITCH_WITH_FLOAT(Expr, B) \ + do { \ + switch (Expr) { \ + TYPE_SWITCH_CASE(PT_Sint8, B) \ + TYPE_SWITCH_CASE(PT_Uint8, B) \ + TYPE_SWITCH_CASE(PT_Sint16, B) \ + TYPE_SWITCH_CASE(PT_Uint16, B) \ + TYPE_SWITCH_CASE(PT_Sint32, B) \ + TYPE_SWITCH_CASE(PT_Uint32, B) \ + TYPE_SWITCH_CASE(PT_Sint64, B) \ + TYPE_SWITCH_CASE(PT_Uint64, B) \ + TYPE_SWITCH_CASE(PT_IntAP, B) \ + TYPE_SWITCH_CASE(PT_IntAPS, B) \ + TYPE_SWITCH_CASE(PT_Bool, B) \ + TYPE_SWITCH_CASE(PT_Float, B) \ + default: \ + llvm_unreachable("Unhandled bitcast type"); \ + } \ + } while (0) + +/// Rotate things around for big endian targets. +static void swapBytes(std::byte *M, size_t N) { + for (size_t I = 0; I != (N / 2); ++I) + std::swap(M[I], M[N - 1 - I]); +} + +/// Track what bits have been initialized to known values and which ones +/// have indeterminate value. +/// All offsets are in bits. +struct BitTracker { + llvm::BitVector Initialized; + llvm::BitVector Data; ---------------- sethp wrote: I tried `llvm::BitVector` to work for me in #74775 , but it was a little awkward; the operations that I ended up wanting from the buffer's backing store for (cross-endian) bit fields were: * [`getBits(src, [start, end])`](https://github.com/llvm/llvm-project/blob/2e0d3f81e4f5b623bb476bfac0278cfc6d1bd4bc/clang/lib/AST/ExprConstant.cpp#L7114) , which looks very much like what `getBytes` here would need (at a byte granularity) * [`copyBitsFrom(dst, [dstStart, dstEnd], src, ...)`](https://github.com/llvm/llvm-project/blob/2e0d3f81e4f5b623bb476bfac0278cfc6d1bd4bc/clang/lib/AST/ExprConstant.cpp#L7126-L7127), i.e. `pushData`'s bread and butter * [`clearBits(dst, [start, end])`](https://github.com/llvm/llvm-project/blob/2e0d3f81e4f5b623bb476bfac0278cfc6d1bd4bc/clang/lib/AST/ExprConstant.cpp#L7139), this started off being `setBits`; it's basically the same underlying op for `markUninitializedUntil` I ended up going with `APInt` as the alternate spelling for `BitVector` because it exposed those operations more or less directly (as `extractBits`, `insertBits`, and `~setBits` respectively), and it meant two fewer copies to get data into & out of the buffer—especially after extending `copyBitsFrom` to take a `[srcStart, srcEnd]` range. Plus, it ended up being very helpful to use the bit-twiddling operators (`&`/`|`/`~`/ `<<`, etc.) at least in the prototype/debugging stages to get my head around what was going on, but more on that later. The main difference that I saw (besides APInt supporting far more operations) was that `BitVector`s were grow-able, but I'm not sure that helps here: we should know the size of the object at BitTracker-initialization time, right? Here, I think another difference is that the end "pointer" of the BitVector is keeping track of where to write to next; I like that, though it'll take some care to make sure it works with cross-endian bit-fields I think. Either way, `BitTracker` could also offer that simply by tracking its own bit-sized end pointer. https://github.com/llvm/llvm-project/pull/68288 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
