SIGFPE on ragdoll physics

[yvt]

OpenSpades`spades::client::Corpse::Spring:
...
    0x100620aa0 <+400>:  mulss  %xmm6, %xmm2
    0x100620aa4 <+404>:  mulss  %xmm2, %xmm0
    0x100620aa8 <+408>:  mulss  %xmm7, %xmm0
    0x100620aac <+412>:  movss  (%rbx), %xmm2             ; xmm2 = mem[0],zero,zero,zero
    0x100620ab0 <+416>:  addss  %xmm0, %xmm2
    0x100620ab4 <+420>:  movss  %xmm2, (%rbx)
    0x100620ab8 <+424>:  movb   (%rcx), %al
    0x100620aba <+426>:  testb  %al, %al
    0x100620abc <+428>:  jne    0x100620e78               ; <+1384> [inlined] spades::Vector3::operator+=(spades::Vector3 const&) at Corpse.cpp:124
    0x100620ac2 <+434>:  movq   %rbx, -0x38(%rbp)
    0x100620ac6 <+438>:  movb   (%rdx), %al
    0x100620ac8 <+440>:  testb  %al, %al
    0x100620aca <+442>:  jne    0x100620e95               ; <+1413> [inlined] spades::Vector3::operator+=(spades::Vector3 const&) + 29 at Corpse.cpp:124
    0x100620ad0 <+448>:  movaps %xmm5, %xmm3
->  0x100620ad3 <+451>:  divps  %xmm4, %xmm3
    0x100620ad6 <+454>:  movaps %xmm0, %xmm2
    0x100620ad9 <+457>:  divss  %xmm7, %xmm2

(lldb) po (float __attribute__((ext_vector_type(4)))) $xmm4
(0.162500009, 0.162500009, 0, 0)

(lldb) po (float __attribute__((ext_vector_type(4)))) $xmm3
(0.00000334322158, 0.000603287306, 0, 0)

(lldb) po/x $mxcsr
0x00001f21

Apparently, LLVM's SLP vectorizer assumes that all floating point exceptions are masked (thus FP instructions never signal), which is the default setting, in order to take advantage of SIMD instructions even if the number of elements is fewer than the native SIMD width. However it isn't the case in this particular instance.

Curiously, when I inspect the value of mxcsr of every thread, only the threads started by GlobalDispatchThreadPool have its _MM_MASK_INVALID (0x80) bit cleared.

Confirmed on macOS 10.14 Mojave