skan added a comment. In D70157#1788445 <https://reviews.llvm.org/D70157#1788445>, @reames wrote:
> Specifically on the revised patch, I remain confused by the need for multiple > subtypes. The need for fragments *between* the potentially fused > instructions doesn't make sense to me. What I was expecting to see was the > following: > BoundaryAlign w/target=the branch fragment > .. some possibly empty sequence of fragments (i.e. the test/cmp/etc..) ... > the branch fragment > a new data fragment if the branch fragment was a DF > > (i.e. a single BounaryAlign fragment which aligns a payload which is defined > as "next fragment to target fragment inclusive".) > > To be specific, I'd expect to see the following for an example fused sequence: > > 1. BoundaryAlign w/Target = 3 > 2. DataFragment containing TEST RAX, RAX > 3. RelaxeableFragment containing JNE symbo > > Why do we need anything between the two fragments of the fused pair? > > (As a reminder, I am new to this code. If I'm missing the obvious, please > just point it out.) JUMP is not always emiteed into `MCRelaxableFragment`, it also can be emitted into `MCDataFragment` and arithmetic ops with constant arguments of unknown value (e.g. ADD,AND) can be emitted into 'MCRelaxableFragment' , you can find related code in `MCObjectStreamer::EmitInstructionImpl`, 'X86AsmBackend::mayNeedRelaxation'. Let's say JCC is fused with TEST, there are four possible positions for JCC and CMP 1. JCC and CMP are in same `MCDataFragment` 2. JCC and CMP are in two different `MCDataFragment` 3. JCC and CMP are in two different `MCRelaxableFragment` 4. JCC in a `MCRelaxableFragment`, CMP is in a `MCDataFragment` and since `MCCompactEncodedInstFragment` is not applicable yet, i don't what's its behaviour. In order to compute the total size of CMP and JCC in `MCAssembler::relaxBoundaryAlign`, I insert a `FusedJccSplit` to force CMP and JCC in two fragments. Do you have any better idea? CHANGES SINCE LAST ACTION https://reviews.llvm.org/D70157/new/ https://reviews.llvm.org/D70157 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
