Commit Graph

6 Commits

Author SHA1 Message Date
Sam Parker 5618e9be37 [RDA][ARM] collectKilledOperands across multiple blocks
Use MIOperand in collectLocalKilledOperands to make the search
global, as we already have to search for global uses too. This
allows us to delete more dead code when tail predicating.

Differential Revision: https://reviews.llvm.org/D75167
2020-03-03 15:23:05 +00:00
Sam Parker 965ba4291a Revert "[ARM] Add CPSR as an implicit use of t2IT"
This reverts commit e58229fded.

Differential Revision: https://reviews.llvm.org/D75186
2020-02-27 15:43:44 +00:00
Sam Parker e58229fded [ARM] Add CPSR as an implicit use of t2IT
This use is already attached to the BUNDLE instruction but is lost
after finalisation.

Differential Revision: https://reviews.llvm.org/D75186
2020-02-27 10:10:40 +00:00
Sjoerd Meijer 7efabe5c7d [MIR][ARM] MachineOperand comments
This adds infrastructure to print and parse MIR MachineOperand comments.
The motivation for the ARM backend is to print condition code names instead of
magic constants that are difficult to read (for human beings). For example,
instead of this:

  dead renamable $r2, $cpsr = tEOR killed renamable $r2, renamable $r1, 14, $noreg
  t2Bcc %bb.4, 0, killed $cpsr

we now print this:

  dead renamable $r2, $cpsr = tEOR killed renamable $r2, renamable $r1, 14 /* CC::always */, $noreg
  t2Bcc %bb.4, 0 /* CC:eq */, killed $cpsr

This shows that MachineOperand comments are enclosed between /* and */. In this
example, the EOR instruction is not conditionally executed (i.e. it is "always
executed"), which is encoded by the 14 immediate machine operand. Thus, now
this machine operand has /* CC::always */ as a comment. The 0 on the next
conditional branch instruction represents the equal condition code, thus now
this operand has /* CC:eq */ as a comment.

As it is a comment, the MI lexer/parser completely ignores it. The benefit is
that this keeps the change in the lexer extremely minimal and no target
specific parsing needs to be done. The changes on the MIPrinter side are also
minimal, as there is only one target hooks that is used to create the machine
operand comments.

Differential Revision: https://reviews.llvm.org/D74306
2020-02-24 14:19:21 +00:00
Sam Parker a67eb221e2 [RDA][ARM][LowOverheadLoops] Iteration count IT blocks
Change the way that we remove the redundant iteration count code in
the presence of IT blocks. collectLocalKilledOperands has been
introduced to scan an instructions operands, collecting the killed
instructions and then visiting them too. This is used to delete the
code in the preheader which calculates the iteration count. We also
track any IT blocks within the preheader and, if we remove all the
instructions from the IT block, we also remove the IT instruction.
isSafeToRemove is used to remove any redundant uses of the iteration
count within the loop body.

Differential Revision: https://reviews.llvm.org/D74975
2020-02-24 13:51:03 +00:00
Sjoerd Meijer 01022af5d5 [ARM][MVE] LowOverheadLoops: DCE on the iteration count setup expression
Once we have created a tail-predicated hardware-loop, and thus know the number
of elements that are processed, we want to clean-up the iteration count
expression of that loop. In D73682, we bailed the analysis on conditionally
executed instructions. This adds support for IT-blocks, so that we can handle
these cases again. The restriction is that we only support IT blocks containing
1 statement, but that seems to cover most cases and forms of the iteration
count expression.

Differential Revision: https://reviews.llvm.org/D73947
2020-02-05 15:15:46 +00:00