[x86] Bug fix where a new iteration of Pass 1 wasn't always requested

Summary

This merge request fixes a case where an x86 peephole optimisation did not flag the compiler to run another iteration of Pass 1 upon a deep optimisation with MOV instructions, thus possibly missing out on other optimisations.

System

• Processor architecture: i386, x86_64

What is the current bug behavior?

Code under -O2 and above may not be as efficient as it could be.

What is the behavior after applying this patch?

Fewer optimisation opportunities are missed.

Relevant logs and/or screenshots

Most of the changes are from modifying registers to minimise pipeline stalls. For example, under -O4, x86_64-win64 in the inifiles unit - before:

	...
	movq	%rcx,%rbx
	movq	%rdx,%rsi
	movq	%r8,%rdi
	movq	%r9,%r12
	movq	%rdx,%rax
	testq	%rdx,%rdx
	je	.Lj951
	movq	-8(%rdx),%rax
.Lj951:
	testq	%rax,%rax
	setgb	%dl
	movq	%r8,%rax
	testq	%rdi,%rdi
	je	.Lj952
	movq	-8(%rdi),%rax
.Lj952:
	...

After:

	...
	movq	%rcx,%rbx
	movq	%rdx,%rsi
	movq	%r8,%rdi
	movq	%r9,%r12
	movq	%rdx,%rax
	testq	%rdx,%rdx
	je	.Lj951
	movq	-8(%rdx),%rax
.Lj951:
	testq	%rax,%rax
	setgb	%dl
	movq	%r8,%rax
	testq	%r8,%r8 ; <- %rdi changed to %r8
	je	.Lj952
	movq	-8(%r8),%rax ; <- %rdi changed to %r8
.Lj952:
	...

The improvements likely give no improvement to execution speed due to the distance of the MOV instructions from the ones that are changed, but may provide a cascade of additional optimistions in some situations as well as in future development.

Additional Notes

The fix was made by setting the "force new iteration" flag, since the current instruction isn't actually changed. In addition, a nearby Result := True; statement was changed into setting this flag due to the current instruction not being changed and control flow returning to the start of an internal while loop, which continues to do more work with the current instruction. In other words, this improves compiler speed by potentially removing an additional and unnecessary procedure call on the current instruction.