[gcc/devel/rust/master] Merge #870

[gcc/devel/rust/master] Merge #870

[Thomas Schwinge]

https://gcc.gnu.org/g:b21caeb3af4313016afeb94a91956e8fc4c2656d

commit b21caeb3af4313016afeb94a91956e8fc4c2656d
Merge: 03e56b51815 93554f3bce5
Author: bors[bot] <26634292+bors[bot]@users.noreply.github.com>
Date:   Fri Jan 14 15:49:07 2022 +0000

    Merge #870
    
    870: Add constant folding to const functions r=philberty a=philberty
    
    In Rust the ArrayType has a constant capacity constraint, which means it
    allows for bounds checking at compile time as no variable-length arrays are
    allowed. In order to typecheck this case we had a constant folding pass as
    part of the type checking system which generated gcc tree's for the IR
    and enforced the constant checking along the way.
    
    GCC with optimizations turned on is capable of constant folding/propogating
    the compilation unit fully, but we need a method that works regardless of
    middlle-end optimizations to fold constant expressions at the front-end,
    turns out the CPP front-end already does this via its constexpr
    mechanism to ensure that these _do_ fold correctly. Another major reason
    to do this change is that the original const fold pass was a striped down
    copy of what the backend is _already_ doing which is creating a duplication
    of the code generation pass. With this all unified into the code generation
    pass all we need to do is port over gcc/cp/constexpr.c to enforce the const
    rules fully but at the GCC tree level not at the typed HIR level.
    
    Now that we have unified the pass when we hit a const function we can
    simply emit a normal GCC function and outside of const expressions GCC
    will simply emit a normal CallExpr and depending on optimization level
    fully optimize this. If we are in a ConstDecl we will follow the
    rust-constexpr.cc and fold the values or error_mark_node with an apropriate
    error. By reusing the CPP constexpr code we _know_ it works so reusing it
    as much as possible is a good idea in general for this front-end.
    
    Fixes #799
    
    
    Co-authored-by: Philip Herron <philip.herron@embecosm.com>

Diff:

 gcc/rust/Make-lang.in                              |   4 +-
 gcc/rust/ast/rust-item.h                           |   7 +-
 gcc/rust/backend/rust-compile-base.h               |  11 +-
 gcc/rust/backend/rust-compile-context.h            |   6 +-
 gcc/rust/backend/rust-compile-expr.cc              | 235 +++++++++-
 gcc/rust/backend/rust-compile-expr.h               |  81 +---
 gcc/rust/backend/rust-compile-implitem.h           |   4 +-
 gcc/rust/backend/rust-compile-item.h               |  89 +++-
 gcc/rust/backend/rust-compile-pattern.cc           |  33 +-
 gcc/rust/backend/rust-compile-resolve-path.cc      |  23 +-
 gcc/rust/backend/rust-compile-stmt.h               |   4 +-
 gcc/rust/backend/rust-compile-type.cc              |  14 +-
 gcc/rust/backend/rust-compile-type.h               |   5 +-
 gcc/rust/backend/rust-compile.cc                   |  90 +++-
 gcc/rust/backend/rust-constexpr.cc                 | 428 ++++++++++++++++++
 .../rust-constexpr.h}                              |  39 +-
 gcc/rust/hir/rust-ast-lower-base.h                 |   3 +
 gcc/rust/hir/rust-ast-lower-item.h                 |   5 +-
 gcc/rust/hir/rust-ast-lower.cc                     |  28 ++
 gcc/rust/hir/tree/rust-hir-expr.h                  | 170 +++++--
 gcc/rust/hir/tree/rust-hir-item.h                  |   6 +-
 gcc/rust/hir/tree/rust-hir.h                       |  69 ++-
 gcc/rust/rust-backend.h                            |   5 -
 gcc/rust/rust-gcc.cc                               |  42 +-
 gcc/rust/rust-session-manager.cc                   |   4 -
 gcc/rust/typecheck/rust-hir-const-fold-base.h      |  54 ---
 gcc/rust/typecheck/rust-hir-const-fold.cc          | 138 ------
 gcc/rust/typecheck/rust-hir-const-fold.h           | 499 ---------------------
 gcc/rust/typecheck/rust-hir-type-check-enumitem.h  |  20 +-
 gcc/rust/typecheck/rust-hir-type-check-expr.h      | 149 +++---
 gcc/rust/typecheck/rust-hir-type-check-implitem.h  |   3 -
 gcc/rust/typecheck/rust-hir-type-check-stmt.h      |   5 +-
 gcc/rust/typecheck/rust-hir-type-check-toplevel.h  |   3 -
 gcc/rust/typecheck/rust-hir-type-check-type.cc     |  23 +
 gcc/rust/typecheck/rust-hir-type-check.cc          |  23 -
 gcc/rust/typecheck/rust-tyty-cast.h                |  16 +-
 gcc/rust/typecheck/rust-tyty-cmp.h                 |   7 -
 gcc/rust/typecheck/rust-tyty-coercion.h            |  16 +-
 gcc/rust/typecheck/rust-tyty-rules.h               |  16 +-
 gcc/rust/typecheck/rust-tyty.cc                    |  15 +-
 gcc/rust/typecheck/rust-tyty.h                     |  54 ++-
 gcc/testsuite/rust/compile/arrays2.rs              |   3 +-
 gcc/testsuite/rust/execute/torture/const_fold1.rs  |  13 +
 gcc/testsuite/rust/execute/torture/const_fold2.rs  |  16 +
 44 files changed, 1350 insertions(+), 1128 deletions(-)