Makes PyCallable dimension reversing logic consistent with that of PythonExtensionGen by jiawen · Pull Request #8931 · halide/Halide

jiawen · 2026-02-04T00:18:54Z

When a generator emits a Python extension, the pipeline only accepts buffers that are C or F contiguous (PythonExtensionGen.cpp), throwing an exception if it's neither.

In contrast, a callable constructed from generator.compile_to_callable() constructs a pipeline that always reverses the dimensions of input buffers. It also non-contiguous buffers.

This PR changes the latter to be consistent with the former. Callables constructed from generator.compile_to_callable() now:

Reverses the order of dimensions if a buffer is C-contiguous.
Does not reverse the order of dimensions if a buffer is F-contiguous.
Rejects other buffers.

jiawen · 2026-02-04T00:19:26Z

doc/BuildingHalideWithCMake.md

+brew install clang-format lld llvm flatbuffers wabt python pybind11 doxygen eigen libpng libjpeg-turbo openblas
 ```

-The `llvm` package includes `clang`, `clang-format`, and `lld`, too. To ensure


Homebrew pulled these out long ago.

jiawen · 2026-02-04T00:19:49Z

doc/BuildingHalideWithCMake.md


 ```shell
-$ pipx install cmake
+pipx install cmake


Sorry for the drive-by. My vs code auto-formatted this entire file - but for the better I think.

After the changes we've made to CI and Python dependency management in #8942, we should revert this file and consider improvements in a separate PR.

python_bindings/src/halide/halide_/PyBuffer.h

python_bindings/src/halide/halide_/PyCallable.cpp

…ExtensionGen

jiawen · 2026-02-04T00:24:53Z

I'll work on how hl.Buffer wraps existing Buffers in a followup PR?

jiawen · 2026-02-04T00:28:39Z

python_bindings/test/correctness/callable.py

@@ -1,4 +1,5 @@
 import halide as hl
+import numpy as np


Are we ok with this requirement for the test?

Yes, unless it's very incidental. Numpy is all but in the standard Python library at this point.

jiawen · 2026-02-13T18:27:19Z

@alexreinking PTAL?

alexreinking

The code changes look good. Please drop the doc changes from this; we need a bigger update as a separate work item.

alexreinking · 2026-02-13T18:55:54Z

README.md

 Halide requires C++17 (or later) to use.

-For more detail about what Halide is, see https://halide-lang.org.
+For more detail about what Halide is, see <https://halide-lang.org>.


Same thing here. Separate PR for this.

jiawen · 2026-02-13T19:35:20Z

@alexreinking Reverted doc changes.

alexreinking · 2026-02-13T20:58:46Z

@jiawen


C:\PROGRA~1\MICROS~1\2022\COMMUN~1\VC\Tools\MSVC\1444~1.352\bin\Hostx64\x64\cl.exe  /nologo /TP -DHALIDE_ENABLE_RTTI -DHALIDE_VERSION_MAJOR=22 -DHALIDE_VERSION_MINOR=0 -DHALIDE_VERSION_PATCH=0 -DHALIDE_WITH_EXCEPTIONS -DHalide_Python_EXPORTS -DPy_NO_LINK_LIB -IC:\build_bot\worker\halide-llvm_main-x86-64-windows\halide-build\include -IC:\build_bot\worker\halide-llvm_main-x86-64-windows\halide-source\src\runtime -external:IC:\Python311\Include -external:IC:\build_bot\worker\halide-llvm_main-x86-64-windows\halide-build\vcpkg_installed\x64-windows\include -external:W0 /DWIN32 /D_WINDOWS /EHsc /O2 /Ob2 /DNDEBUG -std:c++17 -MD /bigobj /MP /showIncludes /Fopython_bindings\src\halide\CMakeFiles\Halide_Python.dir\halide_\PyCallable.cpp.obj /Fdpython_bindings\src\halide\CMakeFiles\Halide_Python.dir\ /FS -c C:\build_bot\worker\halide-llvm_main-x86-64-windows\halide-source\python_bindings\src\halide\halide_\PyCallable.cpp
C:\build_bot\worker\halide-llvm_main-x86-64-windows\halide-source\python_bindings\src\halide\halide_\PyCallable.cpp(51): error C2065: 'ssize_t': undeclared identifier
C:\build_bot\worker\halide-llvm_main-x86-64-windows\halide-source\python_bindings\src\halide\halide_\PyCallable.cpp(51): error C2146: syntax error: missing ';' before identifier 'c_stride'
C:\build_bot\worker\halide-llvm_main-x86-64-windows\halide-source\python_bindings\src\halide\halide_\PyCallable.cpp(51): error C2065: 'c_stride': undeclared identifier
C:\build_bot\worker\halide-llvm_main-x86-64-windows\halide-source\python_bindings\src\halide\halide_\PyCallable.cpp(52): error C2065: 'ssize_t': undeclared identifier
C:\build_bot\worker\halide-llvm_main-x86-64-windows\halide-source\python_bindings\src\halide\halide_\PyCallable.cpp(52): error C2146: syntax error: missing ';' before identifier 'f_stride'
C:\build_bot\worker\halide-llvm_main-x86-64-windows\halide-source\python_bindings\src\halide\halide_\PyCallable.cpp(52): error C2065: 'f_stride': undeclared identifier
C:\build_bot\worker\halide-llvm_main-x86-64-windows\halide-source\python_bindings\src\halide\halide_\PyCallable.cpp(58): error C2065: 'c_stride': undeclared identifier
C:\build_bot\worker\halide-llvm_main-x86-64-windows\halide-source\python_bindings\src\halide\halide_\PyCallable.cpp(61): error C2065: 'c_stride': undeclared identifier
C:\build_bot\worker\halide-llvm_main-x86-64-windows\halide-source\python_bindings\src\halide\halide_\PyCallable.cpp(63): error C2065: 'f_stride': undeclared identifier
C:\build_bot\worker\halide-llvm_main-x86-64-windows\halide-source\python_bindings\src\halide\halide_\PyCallable.cpp(66): error C2065: 'f_stride': undeclared identifier

Unfortunately, ssize_t isn't a thing on Windows.

alexreinking · 2026-02-13T21:00:02Z

python_bindings/src/halide/halide_/PyCallable.cpp

+void is_any_contiguous(const py::buffer_info &info, bool &c_contig, bool &f_contig) {
+    ssize_t c_stride = info.itemsize;
+    ssize_t f_stride = info.itemsize;
+    c_contig = true;
+    f_contig = true;


While we're changing things here for ssize_t, I'd rather this returned a std::pair and we could use structured bindings below to unpack them.

You can probably get away with auto for the type of *_stride.

I wasted a bunch of time tracking down where ssize_t is defined in PyBind11. py::buffer_info calls it ssize_t, but it's really py::ssize_t and an alias for Py_ssize_t. I didn't realize that ssize_t is POSIX and not part of C. 😠

Well, glad you got to the bottom of it! py::ssize_t is probably nicer to read than auto? Up to you.

alexreinking · 2026-02-13T21:00:29Z

python_bindings/src/halide/halide_/PyCallable.cpp

+                    bool c_contig;
+                    bool f_contig;
+                    is_any_contiguous(value_buffer_info, c_contig, f_contig);


Suggested change

bool c_contig;

bool f_contig;

is_any_contiguous(value_buffer_info, c_contig, f_contig);

auto [c_contig, f_contig] = is_any_contiguous(value_buffer_info);

Grudgingly ok. C++ lawyers at Google would scren "use a struct and name your fields!"

If it were used in two places or not in an anonymous namespace, I would have suggested that. 🙂

Aside: I'm generally more concerned about unexpected non-initialization (sneaky) than switching values around (typically loud logic bugs).

jiawen commented Feb 4, 2026

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jiawen commented Feb 4, 2026

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Makes PyCallable dimension reversing logic consistent with that of Py…

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…ExtensionGen

jiawen force-pushed the jiawen-pycallable branch from a450b21 to 0fffb5b Compare February 4, 2026 00:23

jiawen requested review from abadams and alexreinking February 4, 2026 00:24

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jiawen commented Feb 4, 2026

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alexreinking requested changes Feb 13, 2026

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jiawen added 2 commits February 13, 2026 11:33

revert docs

5ce6afc

Merge remote-tracking branch 'origin/main' into jiawen-pycallable

38df05f

jiawen requested a review from alexreinking February 13, 2026 19:35

alexreinking approved these changes Feb 13, 2026

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jiawen commented Feb 13, 2026

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