[PATCH] D81558: [NewPM] Introduce PreserveCFG check

[Yevgeny Rouban via Phabricator via llvm-commits]

yrouban updated this revision to Diff 289100.
yrouban added a comment.

Defined a separate class named //CFG//.
CFG defines the notion //PreserveCFG// for the multigraph of BasicBlocks with unordered successors.
CFG can safely track and print CFG changes. To guard CFG from accessing deleted blocks //PoisoningVH// is used and is extended with one getter.
The cfg diff printing function is rewritten.
Rebased.

Here is an example of an output of a unexpected CFG change detected after SimplifyCFG mistakenly reported PreservedCFG.

$ opt -passes=simplifycfg -S -verify-cfg-preserved --debug-only=stdinstrumentations

before SimplifyCFG
------------------

  define i32 @test5(i32 %A) {
    switch i32 %A, label %return [
      i32 2, label %return
      i32 10, label %2
      i32 9, label %1
      i32 8, label %2
    ]
  
    ret i32 1
  
    ret i32 2
  
  return:
    ret i32 0
  }

after SimplifyCFG
-----------------

  define i32 @test5(i32 %A) {
    switch i32 %A, label %return [
      i32 8, label %2
      i32 10, label %2
      i32 9, label %1
    ]
  
  1:                                                ; preds = %return, %2, %0
    %merge = phi i32 [ 1, %0 ], [ 2, %2 ], [ 0, %return ]
    ret i32 %merge
  
  2:                                                ; preds = %0, %0
    br label %1
  
  return:                                           ; preds = %0
    br label %1
  }



Mocked error
------------

  Error: SimplifyCFGPass reported it preserved CFG, but changes detected:
  In function @test5
  Different number of non-leaf basic blocks: before=1, after=3
  Non-leaf block return<0x23931c0> is added (1 successors)
  Different successors of block entry<0x2393130> (unordered):
  - before (3): return<0x23931c0>(2), unnamed_1<0x2393990>, unnamed_2<0x23938d0>(2),
  - after (3): return<0x23931c0>, unnamed_1<0x2393990>, unnamed_2<0x23938d0>(2),
  Non-leaf block unnamed_2<0x23938d0> is added (1 successors)
  LLVM ERROR: Preserved CFG changed by SimplifyCFGPass


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D81558/new/

https://reviews.llvm.org/D81558

Files:
  llvm/include/llvm/IR/ValueHandle.h
  llvm/include/llvm/Passes/StandardInstrumentations.h
  llvm/lib/Passes/StandardInstrumentations.cpp

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