[PATCH] D70157: Align branches within 32-Byte boundary

[annita.zhang via Phabricator via cfe-commits]

annita.zhang added a comment.

In D70157#1787160 <https://reviews.llvm.org/D70157#1787160>, @MaskRay wrote:

>




> There is a precedant: .pushsection/.popsection (MCStreamer::SectionStack). With .push_align_branch/.pop_align_branch, we probably don't need the 'switch-to-default' action.
> 
> I don't know how likely we may ever need nested states (e.g. an `.include` directive inside an .align_branch region where the included file has own idea about branch alignment), but .push/.pop does not seem to be more complex than disable/enable/default.

I rethink about the directives and prefer the .push/.pop pair as @MaskRay suggested. To be specified, I'd suggest to use .push_align_branch_boundary and .pop_align_branch_boundary to align with MC command line options. They will cowork with the command line options and overwrite the options if both are existing.

To be clarified, I described the behavior of the directives from my understanding. Feel free to speak if you have difference opinion.

.push_align_branch_boundary [N,] [instruction,]*

  This directive specifies the beginning of a region which will overwrite the value set by the command line or by the previous directive. It can represent either an enabling or disabling directive controlled by parameter N. 
  N indicates to align the branches within N byte boundary. The default value is 32. If N is 0, it means the branch alignment is off within this region. 
  Instruction specifies types of branches to align. The value is one or multiple values from fused, jcc, jmp, call, ret and indirect. The default value is fused, jcc and jmp. (may change later)

.pop_align_branch_boundary

  This directive specifies the end of a region to align branch boundary. The status will be back to which was set by the previous directive or the one set by the command line if there's no previous directive existing.

I will coordinate with GNU binutils community once we discuss and have agreement with the directives.


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  https://reviews.llvm.org/D70157/new/

https://reviews.llvm.org/D70157