[all-commits] [llvm/llvm-project] a7b2a2: [clang] Improve diagnostics around constexpr limit...

[Timm Baeder via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: a7b2a20f01681186bb6872c077a52e22632db9ad
      https://github.com/llvm/llvm-project/commit/a7b2a20f01681186bb6872c077a52e22632db9ad
  Author: Timm Baeder <tbaeder at redhat.com>
  Date:   2026-07-29 (Wed, 29 Jul 2026)

  Changed paths:
    M clang/include/clang/Basic/DiagnosticASTKinds.td
    M clang/lib/AST/ByteCode/InterpHelpers.h
    M clang/lib/AST/ByteCode/InterpState.cpp
    M clang/lib/AST/ByteCode/State.cpp
    M clang/lib/AST/ByteCode/State.h
    M clang/lib/AST/ExprConstant.cpp
    M clang/test/AST/ByteCode/constexpr-steps.cpp
    M clang/test/AST/ByteCode/dynalloc-limits.cpp
    M clang/test/SemaCXX/constexpr-function-recovery-crash.cpp
    M clang/test/SemaCXX/constexpr-steps.cpp
    M clang/test/SemaCXX/cxx2a-constexpr-dynalloc-limits.cpp
    M clang/test/SemaCXX/cxx2c-expansion-stmts.cpp

  Log Message:
  -----------
  [clang] Improve diagnostics around constexpr limits (#212091)

1) Mention the limit in the "constexpr evaluation hit maximum step
limit" diagnostic as well
2) Move the "use -fconstexpr-steps" instruction to its own note so we
can reuse it for two different diagnostics

For
```c++
struct S {
  constexpr S() {}
};
constexpr S foo[1'500'000] = {};
```
we used to emit
```console
array.cpp:1028:13: error: constexpr variable 'foo' must be initialized by a constant expression
 1028 | constexpr S foo[1'500'000] = {};
      |             ^                ~~
array.cpp:1026:17: note: constexpr evaluation hit maximum step limit; possible infinite loop?
 1026 |   constexpr S() {}
      |                 ^
array.cpp:1028:31: note: in call to 'S()'
 1028 | constexpr S foo[1'500'000] = {};
      |                               ^
```

and now we emit
```console
array.cpp:1028:13: error: constexpr variable 'foo' must be initialized by a constant expression
 1028 | constexpr S foo[1'500'000] = {};
      |             ^                ~~
array.cpp:1026:17: note: constexpr evaluation hit maximum step limit of 1048576; possible infinite loop?
 1026 |   constexpr S() {}
      |                 ^
array.cpp:1028:31: note: in call to 'S()'
 1028 | constexpr S foo[1'500'000] = {};
      |                               ^
array.cpp:1026:17: note: use -fconstexpr-steps= to increase this limit (=0 will remove the limit)
 1026 |   constexpr S() {}
```



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