[x86] Mov0LblCmp0Jne optimisation improvement

Summary

This merge request improves the "Mov0LblCmp0Je -> Mov0JmpLblCmp0Je" optimisation to work when an alignment hint appears before the label.

System

• Processor architecture: i386, x86_64

What is the current bug behavior?

If an alignment hint appears before the label at the moment the peephole optimizer scans the code (the align may get removed later), the "Mov0LblCmp0Je -> Mov0JmpLblCmp0Je" is not performed when it's otherwise possible.

What is the behavior after applying this patch?

More occurrances of "Mov0LblCmp0Je -> Mov0JmpLblCmp0Je" should happen.

Relevant logs and/or screenshots

For a simple case, in the agx86nsm unit of the compiler (x86_64-win64, -O4), before:

	...
	call	ASSEMBLE$_$TEXTERNALASSEMBLEROUTPUTFILE_$__$$_ASMWRITE$SHORTSTRING
	xorb	%dil,%dil
.Lj124:
	testb	%dil,%dil
	je	.Lj128
	...

After:

	...
	call	ASSEMBLE$_$TEXTERNALASSEMBLEROUTPUTFILE_$__$$_ASMWRITE$SHORTSTRING
	xorb	%dil,%dil
	jmp	.Lj128
.Lj124:
	testb	%dil,%dil
	je	.Lj128
	...

A cascade optimisation in the db unit of the RTL, which is made possible by this optimisation using GetNextInstructionUsingReg - before:

	...
.Lj6170:
	movb	$1,%r13b
	jmp	.Lj6174
	...
	xorb	%r13b,%r13b
	addq	$1,(%rbx) ; <-- GetNextInstructionUsingReg can skip over this instruction and look at the label.
.Lj6182:
	testb	%r13b,%r13b
	je	.Lj6170
	...

After:

	...
.Lj6170:
	movb	$1,%r13b
	jmp	.Lj6174
	...
	xorb	%r13b,%r13b
	addq	$1,(%rbx)
	movb	$1,%r13b ; <-- OptPass2JMP replaces "jmp .Lj6170" with copies of the mov and the jmp that appear after that label.
	jmp	.Lj6174
.Lj6182:
	testb	%r13b,%r13b
	je	.Lj6170
	...

Additional notes

With some additional work, the db optimisation can be improved further, especially as xorb %r13b,%r13b now writes a value that is immediately overwritten by movb $1,%r13b. This is not yet caught because that is a Pass 1 optimisation while "Mov0LblCmp0Je -> Mov0JmpLblCmp0Je" is Pass 2.