Add a default constructor to llvm::SuccIterator (gcc15) - #24
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akritkbehera merged 1 commit intoSep 3, 2026
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Compiling llvm/lib/IR/Dominators.cpp against the gcc15 libstdc++ fails with
stl_iterator.h:182: error: no matching constructor for initialization of
'llvm::SuccIterator<llvm::Instruction, llvm::BasicBlock>'
libstdc++ 15 declares std::reverse_iterator's default constructor as
noexcept(noexcept(Iterator())). Asking whether a reverse_iterator over
succ_iterator is default constructible -- the C++20 semiregular check the
ranges code does -- forces that exception specification to be instantiated,
and an error inside an exception specification is hard rather than a SFINAE
failure, so the concept never gets to simply answer "no" and the build dies.
libstdc++ 14 has no such noexcept clause, which is why gcc14 is fine.
SuccIterator declares only the begin (InstructionT *) and end (InstructionT *,
bool) constructors, so it has no default one. PredIterator, right above it in
the same header, already carries "PredIterator() = default;" for this reason.
Add SuccIterator() : Inst(nullptr), Idx(0) {}. A null Inst with Idx == 0 is a
state the class already supports: the end-iterator constructor uses it for
malformed CFGs and index_is_valid() special cases it, so a default constructed
iterator behaves like one over a block with no successors. Zero initialising is
better than "= default" here, which would leave the pointer and the index
indeterminate. There is nothing to backport from upstream -- LLVM main has since
folded SuccIterator into Instruction.
The hunk rewrites the "// begin iterator" comment rather than being a pure
insertion, because bazel's ctx.patch (third_party/repo.bzl applies these with
strip = 1) has been seen to silently skip insertion-only hunks, as with the
oneDNN fmt_consteval patch.
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A new Pull Request was created by @akritkbehera for branch cms/v2.21.0. @akritkbehera, @cmsbuild, @iarspider, @raoatifshad, @smuzaffar can you please review it and eventually sign? Thanks. |
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This pull request is fully signed and it will be integrated in one of the next cms/v2.21.0 IBs after it passes the integration tests. This pull request will now be reviewed by the release team before it's merged. @mandrenguyen, @ftenchini, @sextonkennedy (and backports should be raised in the release meeting by the corresponding L2) |
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