[Valgrind-developers] Literal arg for AND and OR

[Jeremy F. <je...@go...>]

I'm wondering why AND and OR don't get to take anything but TempReg
args.  From inspecting some largish chunks of code (mozilla), almost all
the AND instructions are with a constant.

Is it something to do with the special properties of AND and OR
regarding memcheck verification?

Speaking of which, I presume the intent behind generating:

	movl $0, %reg
	xorl %reg, %reg

is to break the dependency on any previous value of %reg.  Unfortunately
it actually generates the mov in the final code.  I wonder if a better
solution is add a DEFINE UInstr which defines (ie, is considered to
write to) its argument without actually generating any code.

I've hacked up a patch to treat AND and OR the same way as the rest of
that group of instructions, but it is falling over in regalloc with
memcheck.

        J