[PATCH] D94377: [StringExtras] Add a helper class for comma-separated lists

[Kazu Hirata via Phabricator via llvm-commits]

kazu created this revision.
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This patch introduces a helper class SubsequentDelim to simplify loops
that generate a comma-separated lists.

For example, consider the following loop, taken from
llvm/lib/CodeGen/MachineBasicBlock.cpp:

  for (auto I = pred_begin(), E = pred_end(); I != E; ++I) {
    if (I != pred_begin())
      OS << ", ";
    OS << printMBBReference(**I);
  }

The new class allows us to rewrite the loop as:

  SubsequentDelim SD;
  for (auto I = pred_begin(), E = pred_end(); I != E; ++I)
    OS << SD << printMBBReference(**I);

where SD evaluates to the empty string for the first time and ", " for
subsequent iterations.

Unlike interleaveComma, defined in llvm/include/llvm/ADT/STLExtras.h,
SubsequentDelim can accommodate a wider variety of loops, including:

- those that conditionally skip certain items,
- those that need iterators to call getSuccProbability(I), and
- those that iterate over integer ranges.

As an example, this patch cleans up MachineBasicBlock::print.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D94377

Files:
  llvm/include/llvm/ADT/StringExtras.h
  llvm/lib/CodeGen/MachineBasicBlock.cpp
  llvm/unittests/ADT/StringExtrasTest.cpp

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