llvm-objdump does not print arguments to sdot

[alexreinking]

This issue was discovered in LLVM 20.1.8, obtained via Homebrew.

Here's a terminal interaction showing the issue:

% echo "test: sdot v19.4s, v6.16b, v18.16b" > test.S
% /opt/homebrew/opt/llvm@20/bin/clang -c test.S -o test.o -march=armv8.6-a
% /opt/homebrew/opt/llvm@20/bin/llvm-objdump -d test.o

test.o: file format mach-o arm64

Disassembly of section __TEXT,__text:

0000000000000000 <test>:
       0: 4e9294d3      sdot

Clearly the arguments to sdot have been dropped. Strangely, other sets of arguments do appear, albeit with the optional size markers removed:

% echo "test: sdot v0.4s, v1.16b, v2.4b[0]" > test.S
% /opt/homebrew/opt/llvm@20/bin/clang -c test.S -o test.o -march=armv8.6-a
% /opt/homebrew/opt/llvm@20/bin/llvm-objdump -d test.o                    

test.o: file format mach-o arm64

Disassembly of section __TEXT,__text:

0000000000000000 <test>:
       0: 4f82e020      sdot    v0, v1, v2[0]

[llvmbot]

@llvm/issue-subscribers-tools-llvm-objdump

Author: Alex Reinking (alexreinking)

This issue was discovered in LLVM 20.1.8, obtained via Homebrew.

Here's a terminal interaction showing the issue:

% echo "test: sdot v19.4s, v6.16b, v18.16b" > test.S
% /opt/homebrew/opt/llvm@<!-- -->20/bin/clang -c test.S -o test.o -march=armv8.6-a
% /opt/homebrew/opt/llvm@<!-- -->20/bin/llvm-objdump -d test.o

test.o: file format mach-o arm64

Disassembly of section __TEXT,__text:

0000000000000000 &lt;test&gt;:
       0: 4e9294d3      sdot

Clearly the arguments to sdot have been dropped. Strangely, other sets of arguments do appear, albeit with the optional size markers removed:

% echo "test: sdot v0.4s, v1.16b, v2.4b[0]" > test.S
% /opt/homebrew/opt/llvm@<!-- -->20/bin/clang -c test.S -o test.o -march=armv8.6-a
% /opt/homebrew/opt/llvm@<!-- -->20/bin/llvm-objdump -d test.o                    

test.o: file format mach-o arm64

Disassembly of section __TEXT,__text:

0000000000000000 &lt;test&gt;:
       0: 4f82e020      sdot    v0, v1, v2[0]

[jh7370]

CC'ing @smithp35, @MaskRay, @ostannard, perhaps one of you could help? Although the example is a Mach-O input, I suspect it might be more likely to do with the ARM disassembly code.

[ostannard]

This seems to be specific to the Apple assembly syntax, which is used by default for Mach-O objects:

$ echo "[0xd3,0x94,0x92,0x4e]" | /work/llvm/build/bin/llvm-mc --triple=aarch64 -mattr=+dotprod -show-encoding --disassemble --output-asm-variant=0
        sdot    v19.4s, v6.16b, v18.16b         // encoding: [0xd3,0x94,0x92,0x4e]
$ echo "[0xd3,0x94,0x92,0x4e]" | /work/llvm/build/bin/llvm-mc --triple=aarch64 -mattr=+dotprod -show-encoding --disassemble --output-asm-variant=1
        sdot                                    // encoding: [0xd3,0x94,0x92,0x4e]

[smithp35]

Yes. When I tried with yesterday's clang and llvm-objdump (using .inst 0x4e9294d3 and .inst 0x4f82e020 for the instructions ) I get

sdot.o: file format elf64-littleaarch64

Disassembly of section .text:

0000000000000000 <.text>:
       0: 4e9294d3      sdot    v19.4s, v6.16b, v18.16b
       4: 4f82e020      sdot    v0.4s, v1.16b, v2.4b[0]

[llvmbot]

@llvm/issue-subscribers-backend-aarch64

Author: Alex Reinking (alexreinking)

This issue was discovered in LLVM 20.1.8, obtained via Homebrew.

Here's a terminal interaction showing the issue:

% echo "test: sdot v19.4s, v6.16b, v18.16b" > test.S
% /opt/homebrew/opt/llvm@<!-- -->20/bin/clang -c test.S -o test.o -march=armv8.6-a
% /opt/homebrew/opt/llvm@<!-- -->20/bin/llvm-objdump -d test.o

test.o: file format mach-o arm64

Disassembly of section __TEXT,__text:

0000000000000000 &lt;test&gt;:
       0: 4e9294d3      sdot

Clearly the arguments to sdot have been dropped. Strangely, other sets of arguments do appear, albeit with the optional size markers removed:

% echo "test: sdot v0.4s, v1.16b, v2.4b[0]" > test.S
% /opt/homebrew/opt/llvm@<!-- -->20/bin/clang -c test.S -o test.o -march=armv8.6-a
% /opt/homebrew/opt/llvm@<!-- -->20/bin/llvm-objdump -d test.o                    

test.o: file format mach-o arm64

Disassembly of section __TEXT,__text:

0000000000000000 &lt;test&gt;:
       0: 4f82e020      sdot    v0, v1, v2[0]