X86: If we have an instruction that sets a flag and a zero test on the input...

X86: If we have an instruction that sets a flag and a zero test on the input of that instruction try to eliminate the test.

For example
	tzcntl	%edi, %ebx
	testl %edi, %edi
	je	.label

can be rewritten into
	tzcntl	%edi, %ebx
	jb 	.label

A minor complication is that tzcnt sets CF instead of ZF when the input
is zero, we have to rewrite users of the flags from ZF to CF. Currently
we recognize patterns using lzcnt, tzcnt and popcnt.

Differential Revision: http://reviews.llvm.org/D3454

llvm-svn: 208788