[Clang Interpreter] Initial patch for the constexpr interpreter

Summary:
This patch introduces the skeleton of the constexpr interpreter,
capable of evaluating a simple constexpr functions consisting of
if statements. The interpreter is described in more detail in the
RFC. Further patches will add more features.

Reviewers: Bigcheese, jfb, rsmith

Subscribers: bruno, uenoku, ldionne, Tyker, thegameg, tschuett, dexonsmith, mgorny, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64146

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@370476 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 98 insertions, 0 deletions

diff --git a/include/clang/AST/ASTContext.h b/include/clang/AST/ASTContext.h
index 816f665fed..4ce30b7e7e 100644
--- a/include/clang/AST/ASTContext.h
+++ b/include/clang/AST/ASTContext.h
@@ -139,6 +139,12 @@ class FullComment;
 
 } // namespace comments
 
+namespace interp {
+
+class Context;
+
+} // namespace interp
+
 struct TypeInfo {
   uint64_t Width = 0;
   unsigned Align = 0;
@@ -564,6 +570,7 @@ private:
   const TargetInfo *Target = nullptr;
   const TargetInfo *AuxTarget = nullptr;
   clang::PrintingPolicy PrintingPolicy;
+  std::unique_ptr<interp::Context> InterpContext;
 
 public:
   IdentifierTable &Idents;
@@ -573,6 +580,9 @@ public:
   IntrusiveRefCntPtr<ExternalASTSource> ExternalSource;
   ASTMutationListener *Listener = nullptr;
 
+  /// Returns the clang bytecode interpreter context.
+  interp::Context &getInterpContext();
+
   /// Container for either a single DynTypedNode or for an ArrayRef to
   /// DynTypedNode. For use with ParentMap.
   class DynTypedNodeList {
diff --git a/include/clang/Basic/DiagnosticASTKinds.td b/include/clang/Basic/DiagnosticASTKinds.td
index 23502152b4..7732be5659 100644
--- a/include/clang/Basic/DiagnosticASTKinds.td
+++ b/include/clang/Basic/DiagnosticASTKinds.td
@@ -228,6 +228,8 @@ def note_constexpr_bit_cast_invalid_subtype : Note<
 def note_constexpr_bit_cast_indet_dest : Note<
   "indeterminate value can only initialize an object of type 'unsigned char'"
   "%select{, 'char',|}1 or 'std::byte'; %0 is invalid">;
+def err_experimental_clang_interp_failed : Error<
+  "the experimental clang interpreter failed to evaluate an expression">;
 
 def warn_integer_constant_overflow : Warning<
   "overflow in expression; result is %0 with type %1">,
diff --git a/include/clang/Basic/LangOptions.def b/include/clang/Basic/LangOptions.def
index 31aca2b0d6..47f5daffd4 100644
--- a/include/clang/Basic/LangOptions.def
+++ b/include/clang/Basic/LangOptions.def
@@ -288,6 +288,10 @@ BENIGN_LANGOPT(ConstexprCallDepth, 32, 512,
                "maximum constexpr call depth")
 BENIGN_LANGOPT(ConstexprStepLimit, 32, 1048576,
                "maximum constexpr evaluation steps")
+BENIGN_LANGOPT(EnableNewConstInterp, 1, 0,
+               "enable the experimental new constant interpreter")
+BENIGN_LANGOPT(ForceNewConstInterp, 1, 0,
+               "force the use of the experimental new constant interpreter")
 BENIGN_LANGOPT(BracketDepth, 32, 256,
                "maximum bracket nesting depth")
 BENIGN_LANGOPT(NumLargeByValueCopy, 32, 0,
diff --git a/include/clang/Basic/OptionalDiagnostic.h b/include/clang/Basic/OptionalDiagnostic.h
new file mode 100644
index 0000000000..ce6e1d9230
--- /dev/null
+++ b/include/clang/Basic/OptionalDiagnostic.h
@@ -0,0 +1,78 @@
+//===- OptionalDiagnostic.h - An optional diagnostic ------------*- 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
+/// Implements a partial diagnostic which may not be emitted.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_BASIC_OPTIONALDIAGNOSTIC_H
+#define LLVM_CLANG_BASIC_OPTIONALDIAGNOSTIC_H
+
+#include "clang/AST/APValue.h"
+#include "clang/Basic/PartialDiagnostic.h"
+#include "llvm/ADT/APFloat.h"
+#include "llvm/ADT/APSInt.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringRef.h"
+
+namespace clang {
+
+/// A partial diagnostic which we might know in advance that we are not going
+/// to emit.
+class OptionalDiagnostic {
+  PartialDiagnostic *Diag;
+
+public:
+  explicit OptionalDiagnostic(PartialDiagnostic *Diag = nullptr) : Diag(Diag) {}
+
+  template <typename T> OptionalDiagnostic &operator<<(const T &v) {
+    if (Diag)
+      *Diag << v;
+    return *this;
+  }
+
+  OptionalDiagnostic &operator<<(const llvm::APSInt &I) {
+    if (Diag) {
+      SmallVector<char, 32> Buffer;
+      I.toString(Buffer);
+      *Diag << StringRef(Buffer.data(), Buffer.size());
+    }
+    return *this;
+  }
+
+  OptionalDiagnostic &operator<<(const llvm::APFloat &F) {
+    if (Diag) {
+      // FIXME: Force the precision of the source value down so we don't
+      // print digits which are usually useless (we don't really care here if
+      // we truncate a digit by accident in edge cases).  Ideally,
+      // APFloat::toString would automatically print the shortest
+      // representation which rounds to the correct value, but it's a bit
+      // tricky to implement. Could use std::to_chars.
+      unsigned precision = llvm::APFloat::semanticsPrecision(F.getSemantics());
+      precision = (precision * 59 + 195) / 196;
+      SmallVector<char, 32> Buffer;
+      F.toString(Buffer, precision);
+      *Diag << StringRef(Buffer.data(), Buffer.size());
+    }
+    return *this;
+  }
+
+  OptionalDiagnostic &operator<<(const APFixedPoint &FX) {
+    if (Diag) {
+      SmallVector<char, 32> Buffer;
+      FX.toString(Buffer);
+      *Diag << StringRef(Buffer.data(), Buffer.size());
+    }
+    return *this;
+  }
+};
+
+} // namespace clang
+
+#endif
diff --git a/include/clang/Driver/Options.td b/include/clang/Driver/Options.td
index 6aba6744e0..9792239f02 100644
--- a/include/clang/Driver/Options.td
+++ b/include/clang/Driver/Options.td
@@ -838,6 +838,10 @@ def fconstant_cfstrings : Flag<["-"], "fconstant-cfstrings">, Group<f_Group>;
 def fconstant_string_class_EQ : Joined<["-"], "fconstant-string-class=">, Group<f_Group>;
 def fconstexpr_depth_EQ : Joined<["-"], "fconstexpr-depth=">, Group<f_Group>;
 def fconstexpr_steps_EQ : Joined<["-"], "fconstexpr-steps=">, Group<f_Group>;
+def fexperimental_new_constant_interpreter : Flag<["-"], "fexperimental-new-constant-interpreter">, Group<f_Group>,
+  HelpText<"Enable the experimental new constant interpreter">, Flags<[CC1Option]>;
+def fforce_experimental_new_constant_interpreter : Flag<["-"], "fforce-experimental-new-constant-interpreter">, Group<f_Group>,
+  HelpText<"Force the use of the experimental new constant interpreter, failing on missing features">, Flags<[CC1Option]>;
 def fconstexpr_backtrace_limit_EQ : Joined<["-"], "fconstexpr-backtrace-limit=">,
                                     Group<f_Group>;
 def fno_crash_diagnostics : Flag<["-"], "fno-crash-diagnostics">, Group<f_clang_Group>, Flags<[NoArgumentUnused, CoreOption]>,