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authorAlon Zakai <azakai@google.com>2019-12-19 09:04:08 -0800
committerGitHub <noreply@github.com>2019-12-19 09:04:08 -0800
commit4d28d3f32e7f213e300b24bc61c3f0ac9d6e1ab6 (patch)
tree91bffc2d47b1fe4bba01e7ada77006ef340bd138 /third_party/llvm-project/include/llvm/MC/SubtargetFeature.h
parent0048f5b004ddf50e750aa335d0be314a73852058 (diff)
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DWARF parsing and writing support using LLVM (#2520)
This imports LLVM code for DWARF handling. That code has the Apache 2 license like us. It's also the same code used to emit DWARF in the common toolchain, so it seems like a safe choice. This adds two passes: --dwarfdump which runs the same code LLVM runs for llvm-dwarfdump. This shows we can parse it ok, and will be useful for debugging. And --dwarfupdate writes out the DWARF sections (unchanged from what we read, so it just roundtrips - for updating we need #2515). This puts LLVM in thirdparty which is added here. All the LLVM code is behind USE_LLVM_DWARF, which is on by default, but off in JS for now, as it increases code size by 20%. This current approach imports the LLVM files directly. This is not how they are intended to be used, so it required a bunch of local changes - more than I expected actually, for the platform-specific stuff. For now this seems to work, so it may be good enough, but in the long term we may want to switch to linking against libllvm. A downside to doing that is that binaryen users would need to have an LLVM build, and even in the waterfall builds we'd have a problem - while we ship LLVM there anyhow, we constantly update it, which means that binaryen would need to be on latest llvm all the time too (which otherwise, given DWARF is quite stable, we might not need to constantly update). An even larger issue is that as I did this work I learned about how DWARF works in LLVM, and while the reading code is easy to reuse, the writing code is trickier. The main code path is heavily integrated with the MC layer, which we don't have - we might want to create a "fake MC layer" for that, but it sounds hard. Instead, there is the YAML path which is used mostly for testing, and which can convert DWARF to and from YAML and from binary. Using the non-YAML parts there, we can convert binary DWARF to the YAML layer's nice Info data, then convert that to binary. This works, however, this is not the path LLVM uses normally, and it supports only some basic DWARF sections - I had to add ranges support, in fact. So if we need more complex things, we may end up needing to use the MC layer approach, or consider some other DWARF library. However, hopefully that should not affect the core binaryen code which just calls a library for DWARF stuff. Helps #2400
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+//===- llvm/MC/SubtargetFeature.h - CPU characteristics ---------*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file Defines and manages user or tool specified CPU characteristics.
+/// The intent is to be able to package specific features that should or should
+/// not be used on a specific target processor. A tool, such as llc, could, as
+/// as example, gather chip info from the command line, a long with features
+/// that should be used on that chip.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_MC_SUBTARGETFEATURE_H
+#define LLVM_MC_SUBTARGETFEATURE_H
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/MathExtras.h"
+#include <array>
+#include <bitset>
+#include <initializer_list>
+#include <string>
+#include <vector>
+
+namespace llvm {
+
+class raw_ostream;
+class Triple;
+
+const unsigned MAX_SUBTARGET_WORDS = 3;
+const unsigned MAX_SUBTARGET_FEATURES = MAX_SUBTARGET_WORDS * 64;
+
+/// Container class for subtarget features.
+/// This is a constexpr reimplementation of a subset of std::bitset. It would be
+/// nice to use std::bitset directly, but it doesn't support constant
+/// initialization.
+class FeatureBitset {
+ static_assert((MAX_SUBTARGET_FEATURES % 64) == 0,
+ "Should be a multiple of 64!");
+ // This cannot be a std::array, operator[] is not constexpr until C++17.
+ uint64_t Bits[MAX_SUBTARGET_WORDS] = {};
+
+protected:
+ constexpr FeatureBitset(const std::array<uint64_t, MAX_SUBTARGET_WORDS> &B) {
+ for (unsigned I = 0; I != B.size(); ++I)
+ Bits[I] = B[I];
+ }
+
+public:
+ constexpr FeatureBitset() = default;
+ constexpr FeatureBitset(std::initializer_list<unsigned> Init) {
+ for (auto I : Init)
+ set(I);
+ }
+
+ FeatureBitset &set() {
+ std::fill(std::begin(Bits), std::end(Bits), -1ULL);
+ return *this;
+ }
+
+ constexpr FeatureBitset &set(unsigned I) {
+ // GCC <6.2 crashes if this is written in a single statement.
+ uint64_t NewBits = Bits[I / 64] | (uint64_t(1) << (I % 64));
+ Bits[I / 64] = NewBits;
+ return *this;
+ }
+
+ constexpr FeatureBitset &reset(unsigned I) {
+ // GCC <6.2 crashes if this is written in a single statement.
+ uint64_t NewBits = Bits[I / 64] & ~(uint64_t(1) << (I % 64));
+ Bits[I / 64] = NewBits;
+ return *this;
+ }
+
+ constexpr FeatureBitset &flip(unsigned I) {
+ // GCC <6.2 crashes if this is written in a single statement.
+ uint64_t NewBits = Bits[I / 64] ^ (uint64_t(1) << (I % 64));
+ Bits[I / 64] = NewBits;
+ return *this;
+ }
+
+ constexpr bool operator[](unsigned I) const {
+ uint64_t Mask = uint64_t(1) << (I % 64);
+ return (Bits[I / 64] & Mask) != 0;
+ }
+
+ constexpr bool test(unsigned I) const { return (*this)[I]; }
+
+ constexpr size_t size() const { return MAX_SUBTARGET_FEATURES; }
+
+ bool any() const {
+ return llvm::any_of(Bits, [](uint64_t I) { return I != 0; });
+ }
+ bool none() const { return !any(); }
+ size_t count() const {
+ size_t Count = 0;
+ for (auto B : Bits)
+ Count += countPopulation(B);
+ return Count;
+ }
+
+ constexpr FeatureBitset &operator^=(const FeatureBitset &RHS) {
+ for (unsigned I = 0, E = array_lengthof(Bits); I != E; ++I) {
+ Bits[I] ^= RHS.Bits[I];
+ }
+ return *this;
+ }
+ constexpr FeatureBitset operator^(const FeatureBitset &RHS) const {
+ FeatureBitset Result = *this;
+ Result ^= RHS;
+ return Result;
+ }
+
+ constexpr FeatureBitset &operator&=(const FeatureBitset &RHS) {
+ for (unsigned I = 0, E = array_lengthof(Bits); I != E; ++I) {
+ Bits[I] &= RHS.Bits[I];
+ }
+ return *this;
+ }
+ constexpr FeatureBitset operator&(const FeatureBitset &RHS) const {
+ FeatureBitset Result = *this;
+ Result &= RHS;
+ return Result;
+ }
+
+ constexpr FeatureBitset &operator|=(const FeatureBitset &RHS) {
+ for (unsigned I = 0, E = array_lengthof(Bits); I != E; ++I) {
+ Bits[I] |= RHS.Bits[I];
+ }
+ return *this;
+ }
+ constexpr FeatureBitset operator|(const FeatureBitset &RHS) const {
+ FeatureBitset Result = *this;
+ Result |= RHS;
+ return Result;
+ }
+
+ constexpr FeatureBitset operator~() const {
+ FeatureBitset Result = *this;
+ for (auto &B : Result.Bits)
+ B = ~B;
+ return Result;
+ }
+
+ bool operator==(const FeatureBitset &RHS) const {
+ return std::equal(std::begin(Bits), std::end(Bits), std::begin(RHS.Bits));
+ }
+
+ bool operator!=(const FeatureBitset &RHS) const { return !(*this == RHS); }
+
+ bool operator < (const FeatureBitset &Other) const {
+ for (unsigned I = 0, E = size(); I != E; ++I) {
+ bool LHS = test(I), RHS = Other.test(I);
+ if (LHS != RHS)
+ return LHS < RHS;
+ }
+ return false;
+ }
+};
+
+/// Class used to store the subtarget bits in the tables created by tablegen.
+class FeatureBitArray : public FeatureBitset {
+public:
+ constexpr FeatureBitArray(const std::array<uint64_t, MAX_SUBTARGET_WORDS> &B)
+ : FeatureBitset(B) {}
+
+ const FeatureBitset &getAsBitset() const { return *this; }
+};
+
+//===----------------------------------------------------------------------===//
+
+/// Manages the enabling and disabling of subtarget specific features.
+///
+/// Features are encoded as a string of the form
+/// "+attr1,+attr2,-attr3,...,+attrN"
+/// A comma separates each feature from the next (all lowercase.)
+/// Each of the remaining features is prefixed with + or - indicating whether
+/// that feature should be enabled or disabled contrary to the cpu
+/// specification.
+class SubtargetFeatures {
+ std::vector<std::string> Features; ///< Subtarget features as a vector
+
+public:
+ explicit SubtargetFeatures(StringRef Initial = "");
+
+ /// Returns features as a string.
+ std::string getString() const;
+
+ /// Adds Features.
+ void AddFeature(StringRef String, bool Enable = true);
+
+ /// Returns the vector of individual subtarget features.
+ const std::vector<std::string> &getFeatures() const { return Features; }
+
+ /// Prints feature string.
+ void print(raw_ostream &OS) const;
+
+ // Dumps feature info.
+ void dump() const;
+
+ /// Adds the default features for the specified target triple.
+ void getDefaultSubtargetFeatures(const Triple& Triple);
+
+ /// Determine if a feature has a flag; '+' or '-'
+ static bool hasFlag(StringRef Feature) {
+ assert(!Feature.empty() && "Empty string");
+ // Get first character
+ char Ch = Feature[0];
+ // Check if first character is '+' or '-' flag
+ return Ch == '+' || Ch =='-';
+ }
+
+ /// Return string stripped of flag.
+ static std::string StripFlag(StringRef Feature) {
+ return hasFlag(Feature) ? Feature.substr(1) : Feature;
+ }
+
+ /// Return true if enable flag; '+'.
+ static inline bool isEnabled(StringRef Feature) {
+ assert(!Feature.empty() && "Empty string");
+ // Get first character
+ char Ch = Feature[0];
+ // Check if first character is '+' for enabled
+ return Ch == '+';
+ }
+
+ /// Splits a string of comma separated items in to a vector of strings.
+ static void Split(std::vector<std::string> &V, StringRef S);
+};
+
+} // end namespace llvm
+
+#endif // LLVM_MC_SUBTARGETFEATURE_H
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