Hi, Gentle ping.
Thanks, Soumya > On 27 Jan 2026, at 10:32 AM, Soumya AR <[email protected]> wrote: > > 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 >> >
