[PATCH] D100792: [LoopInterchange] Handle lcssa PHIs with multiple predecessors

[Congzhe Cao via Phabricator via llvm-commits]

congzhe added a comment.

Just to better clarify, for the test case added in this patch, this is the IR after loop interchange (with this patch):

  define i64 @lcssa_08([100 x [100 x i64]]* %Arr) {
  entry:
    br label %for2.preheader
  
  for1.header.preheader:                            ; preds = %for2
    br label %for1.header
  
  for1.header:                                      ; preds = %for1.header.preheader, %for1.inc
    %indvars.iv23 = phi i64 [ %indvars.iv.next24, %for1.inc ], [ 0, %for1.header.preheader ]
    br i1 undef, label %for2.split1, label %for2.split
  
  for2.preheader:                                   ; preds = %entry
    br label %for2
  
  for2:                                             ; preds = %for2.preheader, %for2.split
    %indvars.iv = phi i64 [ %1, %for2.split ], [ 0, %for2.preheader ]
    br label %for1.header.preheader
  
  for2.split1:                                      ; preds = %for1.header
    %arrayidx = getelementptr inbounds [100 x [100 x i64]], [100 x [100 x i64]]* %Arr, i64 0, i64 %indvars.iv, i64 %indvars.iv23
    %lv = load i64, i64* %arrayidx, align 4
    %indvars.iv.next.3 = add nuw nsw i64 %indvars.iv, 1
    %exit1 = icmp eq i64 %indvars.iv.next.3, 100
    br label %for1.inc.loopexit
  
  for2.split:                                       ; preds = %for1.inc, %for1.header
    %0 = phi i64 [ %indvars.iv23, %for1.inc ], [ %indvars.iv23, %for1.header ]
    %1 = add nuw nsw i64 %indvars.iv, 1
    %2 = icmp eq i64 %1, 100
    br i1 %2, label %for1.loopexit, label %for2
  
  for1.inc.loopexit:                                ; preds = %for2.split1
    br label %for1.inc
  
  for1.inc:                                         ; preds = %for1.inc.loopexit
    %indvars.iv.next24 = add nuw nsw i64 %indvars.iv23, 1
    %exit2 = icmp eq i64 %indvars.iv.next24, 100
    br i1 %exit2, label %for2.split, label %for1.header
  
  for1.loopexit:                                    ; preds = %for2.split
    %indvars.outer.lcssa = phi i64 [ %0, %for2.split ]
    ret i64 %indvars.outer.lcssa
  }

Without this patch the compiler currently crashes with the following info:

  PHINode should have one entry for each predecessor of its parent basic block!
    %0 = phi i64 [ %indvars.iv23, %for1.inc ]
  in function lcssa_08
  LLVM ERROR: Broken function found, compilation aborted!


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D100792/new/

https://reviews.llvm.org/D100792