There's several, to my eyes, somewhat related looking bugs:
Bug 36743 - Cannot select: X86ISD::CALL ICE with -mx32 -O2 -fno-plt
Bug 34268 - JITting of x32 code on x64 fails with crash or instruction selection error.
There's unfortunately been no investigation.
I'm asking because I hit something eerily looking like the second case,
in postgresql. The debian packagers report that postgres' tests fail on
x32 when llvm support is enabled. The relevant bitcode excerpt and
Is x32 support considered stable?