X86 can generate movb al, eax ?

[llvmbot]

Bugzilla Link	1071
Resolution	INVALID
Resolved on	Feb 22, 2010 12:52
Version	trunk
OS	Linux
Reporter	LLVM Bugzilla Contributor

Extended Description

While testing this function:

define bool i32() { ret bool true; }

I noticed that it is possible for the X86 backend to generate:

movb al, eax

which doesn't assemble.

To make this happen, go to CodeGen/SelectionISel.cpp in the visitRetInst
function and make it not do an extend (of any kind) for boolean. This will
cause the Legalizer to apply an ANY_EXTEND which, presumably, means that not
doing an extend is okay. While that change is not correct, the X86 backend
shouldn't generate incorrect instructions either.

[llvmbot]

Looks like legalizer isn't inserting an anyext to i32 so we ended up with a movb
with a 32-bit register destination.

If you let visitRet insert the anyext node, then it will not generate this
illegal instruction.