Hi, Gentle ping.
Thanks, Soumya > On 19 Jan 2026, at 9:53 PM, [email protected] wrote: > > External email: Use caution opening links or attachments > > > From: Soumya AR <[email protected]> > > Hi, > > The following are a revised set of patches that implement atomic fetch min/max > in GCC. > > These have been revised based on discussions in this thread: > > https://gcc.gnu.org/pipermail/gcc-patches/2025-November/699602.html > > To summarize, we now define the following builtins: > - __atomic_fetch_min > - __atomic_fetch_max > - __atomic_min_fetch > - __atomic_max_fetch > > And resolve them to an internal function: IFN_ATOMIC_FETCH_MINMAX. > > If the backend does not support atomic fetch min/max operations, the IFN is > lowered to a compare-and-swap loop. Otherwise, it is expanded to > target-specific > optabs. > > ---- > > Following discussions with Jonathan here: > https://gcc.gnu.org/pipermail/gcc-patches/2026-January/706015.html > > I suppose implementing the op_fetch variants of the builtins is not necessary. > If they are only used to support the libstdc++ operator overloading, then we > can get rid of them in the compiler if we have no use of exposing these. > > This would also help clean up a lot of extra-handling in place to ensure the > op_fetch variants of min/max are handled correctly. > > ---- > > Patch 2, ie. implementing the builtins in GCC via CAS lowering has had minor > modifications since v1 of it posted here: > > https://gcc.gnu.org/pipermail/gcc-patches/2025-November/700787.html > > Patch 3 and 4 further extend this interface to expand the IFN to atomic > min/max > optabs for aarch64. > > ---- > > Patch 5 adds a pass that pattern-matches CAS loops implementing fetch min/max > to IFN_ATOMIC_FETCH_MINMAX. > > This pass turned out to be a lot more complex than I was expecting so insights > into its implementation would really help. > > I don't expect this patch to go in at Stage 4, but putting it up for feedback > nonetheless, if folks get the time to look at it. > > ---- > Soumya AR (5): > libstdc++: Implement std::atomic::fetch_min/max > middle-end: Add support for atomic fetch min/max builtins via CAS > lowering > expand: Expand IFN_ATOMIC_FETCH_MINMAX to target specific optabs > aarch64: Add backend support for atomic fetch min/max operations > middle-end: Pattern match CAS loops to IFN_ATOMIC_FETCH_MINMAX > > gcc/Makefile.in | 2 + > gcc/builtins.cc | 83 +- > gcc/builtins.h | 1 + > gcc/c-family/c-common.cc | 58 +- > gcc/config/aarch64/aarch64-protos.h | 4 + > gcc/config/aarch64/aarch64.cc | 51 ++ > gcc/config/aarch64/atomics.md | 54 +- > gcc/config/aarch64/iterators.md | 30 +- > gcc/expr.cc | 88 +- > gcc/ifn-atomic-minmax-lowering.cc | 402 +++++++++ > gcc/internal-fn.cc | 8 + > gcc/internal-fn.def | 1 + > gcc/optabs.cc | 133 +++ > gcc/optabs.def | 24 + > gcc/passes.def | 2 + > gcc/sync-builtins.def | 15 + > .../g++.dg/tree-ssa/cas-to-minmax-1.C | 23 + > .../g++.dg/tree-ssa/cas-to-minmax-2.C | 23 + > .../g++.dg/tree-ssa/cas-to-minmax-3.C | 21 + > .../g++.dg/tree-ssa/cas-to-minmax-4.C | 22 + > gcc/testsuite/gcc.dg/atomic-op-1.c | 353 ++++++++ > gcc/testsuite/gcc.dg/atomic-op-2.c | 353 ++++++++ > gcc/testsuite/gcc.dg/atomic-op-3.c | 353 ++++++++ > gcc/testsuite/gcc.dg/atomic-op-4.c | 353 ++++++++ > gcc/testsuite/gcc.dg/atomic-op-5.c | 355 ++++++++ > .../gcc.dg/tree-ssa/cas-to-minmax-1.c | 18 + > .../gcc.dg/tree-ssa/cas-to-minmax-2.c | 18 + > .../gcc.dg/tree-ssa/cas-to-minmax-3.c | 17 + > .../gcc.dg/tree-ssa/cas-to-minmax-4.c | 14 + > .../gcc.dg/tree-ssa/cas-to-minmax-5.c | 19 + > .../gcc.dg/tree-ssa/cas-to-minmax-6.c | 19 + > .../gcc.dg/tree-ssa/cas-to-minmax-run-1.c | 75 ++ > .../gcc.dg/tree-ssa/cas-to-minmax-run-2.c | 55 ++ > .../gcc.target/aarch64/atomic-minmax-lse.c | 122 +++ > .../gcc.target/aarch64/atomic-minmax-nolse.c | 196 +++++ > .../gcc.target/aarch64/atomic-minmax.c | 128 +++ > .../gcc.target/aarch64/atomic-minmax.x | 185 ++++ > gcc/tree-cas-to-minmax.cc | 801 ++++++++++++++++++ > gcc/tree-pass.h | 2 + > libgcc/config/aarch64/lse.S | 62 +- > libgcc/config/aarch64/t-lse | 3 +- > libstdc++-v3/include/bits/atomic_base.h | 132 ++- > libstdc++-v3/include/bits/version.def | 8 + > libstdc++-v3/include/bits/version.h | 10 + > libstdc++-v3/include/std/atomic | 57 ++ > libstdc++-v3/src/c++23/std.cc.in | 6 + > .../nonmembers_fetch_minmax.cc | 50 ++ > .../atomic_ref/integral_fetch_minmax.cc | 118 +++ > 48 files changed, 4823 insertions(+), 104 deletions(-) > create mode 100644 gcc/ifn-atomic-minmax-lowering.cc > create mode 100644 gcc/testsuite/g++.dg/tree-ssa/cas-to-minmax-1.C > create mode 100644 gcc/testsuite/g++.dg/tree-ssa/cas-to-minmax-2.C > create mode 100644 gcc/testsuite/g++.dg/tree-ssa/cas-to-minmax-3.C > create mode 100644 gcc/testsuite/g++.dg/tree-ssa/cas-to-minmax-4.C > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/cas-to-minmax-1.c > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/cas-to-minmax-2.c > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/cas-to-minmax-3.c > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/cas-to-minmax-4.c > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/cas-to-minmax-5.c > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/cas-to-minmax-6.c > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/cas-to-minmax-run-1.c > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/cas-to-minmax-run-2.c > create mode 100644 gcc/testsuite/gcc.target/aarch64/atomic-minmax-lse.c > create mode 100644 gcc/testsuite/gcc.target/aarch64/atomic-minmax-nolse.c > create mode 100644 gcc/testsuite/gcc.target/aarch64/atomic-minmax.c > create mode 100644 gcc/testsuite/gcc.target/aarch64/atomic-minmax.x > create mode 100644 gcc/tree-cas-to-minmax.cc > create mode 100644 > libstdc++-v3/testsuite/29_atomics/atomic_integral/nonmembers_fetch_minmax.cc > create mode 100644 > libstdc++-v3/testsuite/29_atomics/atomic_ref/integral_fetch_minmax.cc > > -- > 2.43.0 >
