[PATCH] D155064: [clang][SemaCXX] Diagnose tautological uses of consteval if and is_constant_evaluated

[Takuya Shimizu via Phabricator via cfe-commits]

hazohelet created this revision.
hazohelet added reviewers: aaron.ballman, rsmith, cor3ntin, erichkeane, tbaeder.
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This patch makes clang diagnose extensive cases of `consteval if` and `is_constant_evaluated` usage that are tautologically true or false.
This introduces a new `Sema::ExpressionEvaluationContext` kind that means the immediate appearance of `if consteval` or `is_constant_evaluated` are tautologically false(e.g. inside `if !consteval {}` block or non-constexpr-qualified function definition body)
This patch also pushes new expression evaluation context when parsing the condition of `if constexpr` and initializer of variables so that Sema can be aware that the use of `consteval if` and `is_consteval` are tautologically true in `if constexpr` condition and `constexpr` variable initializers.
BEFORE this patch, the warning for `is_constant_evaluated` was emitted from constant evaluator. This patch moves the warning logic to Sema in order to diagnose tautological use of `is_constant_evaluated` in the same way as `consteval if`.

Fixes https://github.com/llvm/llvm-project/issues/43760
Fixes https://github.com/llvm/llvm-project/issues/51567


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D155064

Files:
  clang/docs/ReleaseNotes.rst
  clang/include/clang/Basic/DiagnosticASTKinds.td
  clang/include/clang/Basic/DiagnosticSemaKinds.td
  clang/include/clang/Parse/Parser.h
  clang/include/clang/Sema/Sema.h
  clang/lib/AST/ExprConstant.cpp
  clang/lib/Parse/ParseCXXInlineMethods.cpp
  clang/lib/Parse/ParseDecl.cpp
  clang/lib/Parse/ParseDeclCXX.cpp
  clang/lib/Parse/ParseExpr.cpp
  clang/lib/Parse/ParseStmt.cpp
  clang/lib/Sema/SemaDecl.cpp
  clang/lib/Sema/SemaDeclCXX.cpp
  clang/lib/Sema/SemaExpr.cpp
  clang/lib/Sema/SemaExprMember.cpp
  clang/lib/Sema/SemaLambda.cpp
  clang/lib/Sema/SemaStmt.cpp
  clang/test/AST/Interp/builtins.cpp
  clang/test/AST/Interp/if.cpp
  clang/test/AST/Interp/literals.cpp
  clang/test/CXX/expr/expr.const/p2-0x.cpp
  clang/test/CXX/expr/expr.const/p6-2a.cpp
  clang/test/CXX/expr/expr.prim/expr.prim.lambda/p3.cpp
  clang/test/CXX/stmt.stmt/stmt.select/stmt.if/p4.cpp
  clang/test/Parser/pragma-fenv_access.c
  clang/test/SemaCXX/constant-expression-cxx11.cpp
  clang/test/SemaCXX/cxx2a-consteval.cpp
  clang/test/SemaCXX/cxx2b-consteval-if.cpp
  clang/test/SemaCXX/ext-int.cpp
  clang/test/SemaCXX/warn-constant-evaluated-constexpr.cpp
  clang/test/SemaCXX/warn-tautological-meta-constant.cpp
  clang/test/SemaTemplate/concepts.cpp
  clang/unittests/Support/TimeProfilerTest.cpp
  libcxx/test/std/algorithms/alg.modifying.operations/alg.copy/ranges.copy.segmented.pass.cpp
  libcxx/test/std/utilities/meta/meta.const.eval/is_constant_evaluated.verify.cpp

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