amd64 parser drops .zero directives from constant pools, causing VMOVDQA SIGSEGV

[zhangzhenghao]

Bug description

GoAT's amd64 parser drops .zero directives from Clang local constant pools. The generated Go assembly therefore emits a shorter data symbol than the SIMD load expects. An aligned VMOVDQA then reads a truncated/insufficiently aligned symbol and crashes with SIGSEGV.

This is a follow-up to #78: local .LCPI* labels are now retained, but zero-filled ranges inside those pools are still lost.

The bug was found while generating the AVX512 INT4 batch kernel in gorse-io/xvec#79.

Reproduction

Source:

https://github.com/gorse-io/xvec/blob/905592d356ee3b2abdcee5f09620439ad7d2a5cb/internal/ailego/math_batch/src/inner_product_batch_int4_avx512.c

Generate it with the GoAT version currently used by xvec:

go tool goat \
  internal/ailego/math_batch/src/inner_product_batch_int4_avx512.c \
  --target amd64 -O3 -mavx2 -mavx512f -mavx512bw \
  -e=-fno-vectorize -e=-fno-slp-vectorize \
  -o .goat/mathbatch

Clang emits this 16-byte constant pool:

.LCPI0_4:
    .zero   4
    .zero   4
    .long   0
    .long   16

GoAT drops both .zero directives and emits only eight bytes:

DATA __goat_data_2e4c435049305f34<>+0x000(SB)/8, $0x0000001000000000
GLOBL __goat_data_2e4c435049305f34<>(SB), 8, $8

The generated function still performs a 16-byte aligned load:

VMOVDQA __goat_data_2e4c435049305f34<>(SB), X5

Running the generated kernel under qemu-x86_64 -cpu max or on the GitHub Actions AVX512 host crashes at that VMOVDQA. The xvec CI failure is visible in PR #79.

A representative failure is:

unexpected return pc for ...xvec_avx512_batch_inner_products_int4_4
...
inner_product_batch_int4_avx512.s:45
fatal error: unknown caller pc

The unexpected return pc output is secondary: Clang's generated prologue temporarily changes SP, so Go's panic unwinder cannot produce a normal traceback after the SIMD load faults. The first faulting instruction is the VMOVDQA referencing the truncated constant pool.

Expected behavior

GoAT should preserve .zero N as N zero bytes when converting Clang constant pools, so that:

• the generated GLOBL size matches the original constant-pool size;
• subsequent fields retain their original offsets;
• the symbol satisfies the alignment required by aligned SIMD loads.

Alternatively, GoAT should reject unsupported constant-pool directives rather than emit a silently truncated symbol.

Environment

• GoAT: v0.2.2-0.20260924112123-4875656d2845
• Go: go1.27.0 linux/amd64
• Clang: 21.1.8 (6ubuntu1)
• objdump: GNU Binutils 2.46
• Reproduced with qemu-x86_64 -cpu max and in xvec GitHub Actions