nsrip-dd commented on issue #983:
URL: https://github.com/apache/arrow-go/issues/983#issuecomment-5332134569
Regarding `_unpack32_neon`, I don't know if I'll have bandwidth any time
soon to work on this, but I wanted to drop some breadcrumbs here in case
anybody else wants to pick it up.
My high-level thought is that the best approach would be to re-generate the
assembly without using the reserved registers, then re-apply any fixups/manual
changes that have been done since the code was first generated. I had an LLM
take a shot at fixing the assembly in-place but I have low confidence in the
correctness.
We'd start by telling the C compiler not to use the reserved registers:
```diff
diff --git a/parquet/internal/utils/Makefile
b/parquet/internal/utils/Makefile
index f6dce46197..dda1662c6b 100644
--- a/parquet/internal/utils/Makefile
+++ b/parquet/internal/utils/Makefile
@@ -27,7 +27,8 @@
ASM_FLAGS_POPCNT=-mpopcnt
C_FLAGS_NEON=-O3 -fvectorize -mllvm -force-vector-width=16
-fno-asynchronous-unwind-tables -mno-red-zone -mstackrealign -fno-exceptions \
- -fno-rtti -fno-builtin -ffast-math -fno-jump-tables -I_lib
+ -fno-rtti -fno-builtin -ffast-math -fno-jump-tables -I_lib \
+ -ffixed-x28 -ffixed-x27 -ffixed-x18
GO_SOURCES := $(shell find . -path ./_lib -prune -o -name '*.go' -not
-name '*_test.go')
ALL_SOURCES := $(shell find . -path ./_lib -prune -o -name '*.go' -name
'*.s' -not -name '*_test.go')
```
Then `make CC=clang _lib/bit_packing_neon.s` (I don't have clang-11 which is
the default CC value; do we care about the specific clang version?). That'll
give you the assembly from which we can build the Go assembly following the
instructions in the parquet/internal/utils/_lib README file. Then we'd need to
remove the frame pointer setup stuff, at the very least.
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