"Unreachable" exception not thrown correctly on llvm-jit mode

[unicornt]

Test Case

code.zip

Result

fast-jit mode can throw unreachable exception correctly while llvm-jit will throw a segmentation fault

I also ran the same code on other wasm runtimes. They all can report unreachable exception correctly.

Versions and Environment

wamr version : 1.2.3

Operating system: Ubuntu 20.04

Architecture: x86_64

[wenyongh]

Hi, thanks for reporting the issue! I submitted patch set for PR #2697 to fix, could you please apply it, re-compile wamrc and test again?

[unicornt]

Hi, thanks for reporting the issue! I submitted patch set for PR #2697 to fix, could you please apply it, re-compile wamrc and test again?

I tested it with llvm-jit mode and it really works. By the way, issue #2698 I just reported can also be fixed.
And I'm asking for the cause of this bug again. Could you tell me? Thanks a lot!

[wenyongh]

It is related to change in aot_emit_control.c, invalid llvm phi value may be used into the else basic block (use wamrc --format=llvmir-unopt -o test.ll test.wasm):

  %and53 = and i32 %or, %and52
  br label %if0_else

if0_else:                                         ; preds = %func_begin
  %else0_phi0 = phi i32 [ %"local0#", %func_begin ]
  %else0_phi1 = phi i32 [ %add, %func_begin ]
  call void @"aot_func#41"(ptr %exec_env, i32 %if0_phi0, i32 %if0_phi1)   => should use %else0_phi0 and %else0_phi1 but not %if0_phi0 and %if0_phi1
  br label %if0_end

[unicornt]

What is llvm_entry_block variable meaning in the code? Is it used to distinguish block like if0_else and other type of block?

[wenyongh]

llvm_entry_block is the basic block for the wasm opcode BLOCK, LOOP and the first branch of opcode IF, if_else is the basic block of the else branch of opcode IF. Somewhat like:

BLOCK/LOOP                        block0_begin/loop0_begin:   (llvm_entry_block)
  ...                      =>        ...
END                               block0_end/loop0_end:       (llvm_end_block)

IF                        if0_begin:   (llvm_entry_block)
  ...                        ...
ELSE                =>    if0_else:    (llvm_else_block)
  ...                         ...
END                       if0_end:     (llvm_end_block)