[all-commits] [llvm/llvm-project] f933bb: [TableGen] Use guarded assert in constexpr functio...

[Krzysztof Parzyszek via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: f933bbf694b82845d3d25cc4cf77b0486bff1191
      https://github.com/llvm/llvm-project/commit/f933bbf694b82845d3d25cc4cf77b0486bff1191
  Author: Krzysztof Parzyszek <Krzysztof.Parzyszek at amd.com>
  Date:   2026-04-29 (Wed, 29 Apr 2026)

  Changed paths:
    M llvm/test/TableGen/directive1.td
    M llvm/test/TableGen/directive2.td
    M llvm/utils/TableGen/Basic/DirectiveEmitter.cpp

  Log Message:
  -----------
  [TableGen] Use guarded assert in constexpr functions (#194728)

The constexpr functions in question take a scoped enum as an argument
and a switch statement returns a value for each value of the enum. These
are all legal statements in a constexpr function in C++14.

Under constexpr rules, the evaluation of a constexpr function cannot
lead to an evaluation of any prohibited forms of expressions. An
evaluation of the functions being discussed with a valid argument will
terminate at the switch, and an code that follows will not be evaluated.

Using "llvm_unreachable" after the switch should be ok as long as the
expansion of the llvm_unreachable macro does not contain any statements
not allowed to appear in a constexpr function. At the same time, GCC
before v9 did not tolerate any unguarded calls to non-constexpr
functions after the switch.

To avoid using "llvm_unreachable", which can have multiple expansions,
use an assert with an explicit condition that the underlying value of
the argument lies between the minimum and maximum values of the enum.



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