[PATCH] D133313: [Assignment Tracking][18/*] Account for assignment tracking in LICM

[Orlando Cazalet-Hyams via Phabricator via llvm-commits]

Orlando updated this revision to Diff 459435.
Orlando marked 3 inline comments as done.
Orlando added a comment.

+ Address review comments
+ Add CFG diagram to test multi-exit.ll

> you might want to delete tbaa but it's not too important.

Done.

In D133313#3780173 <https://reviews.llvm.org/D133313#3780173>, @jmorse wrote:

> What's the behaviour if there are multiple exit paths from the loop that store different values, like
>
>   if (foo) {
>     var = 1; break;
>   } else if (bar) {
>     var = 2; break;
>   } ...
>
> Presumably there'll be an exit block with a PHI, then a store -- and all the dbg.assigns for 'var' will point at that final store, but will have different value operands? (Just trying to work out what this would look like in my mind.

Yep that's right, here's a reproducer with IR:

  int a, b;
  void esc(int*);
  int fun(int if_cond, int loop_cond) {
    int local = 0;
    while (--loop_cond) {
      if (if_cond) {
        local = a;
      } else {
        local = b;
        esc(&a);
      }
    }
    esc(&local);
    return local;
  }

Before LICM

  ...
  while.body:                                       ; preds = %while.cond
    %tobool1.not = icmp eq i32 %if_cond, 0, !dbg !34
    br i1 %tobool1.not, label %if.else, label %if.then, !dbg !37
  
  if.then:                                          ; preds = %while.body
    %1 = load i32, i32* @a, align 4, !dbg !38, !tbaa !26
    store i32 %1, i32* %local, align 4, !dbg !40, !tbaa !26, !DIAssignID !41
    call void @llvm.dbg.assign(metadata i32 %1, metadata !19, metadata !DIExpression(), metadata !41, metadata i32* %local, metadata !DIExpression()), !dbg !21
    br label %if.end, !dbg !42
  
  if.else:                                          ; preds = %while.body
    %2 = load i32, i32* @b, align 4, !dbg !43, !tbaa !26
    store i32 %2, i32* %local, align 4, !dbg !45, !tbaa !26, !DIAssignID !46
    call void @llvm.dbg.assign(metadata i32 %2, metadata !19, metadata !DIExpression(), metadata !46, metadata i32* %local, metadata !DIExpression()), !dbg !21
    tail call void @_Z3escPi(i32* noundef nonnull @a), !dbg !47
    br label %if.end
  
  if.end:                                           ; preds = %if.else, %if.then
    br label %while.cond, !dbg !31, !llvm.loop !48
  
  ; Exit blocks
  while.end:                                        ; preds = %while.cond
    call void @_Z3escPi(i32* noundef nonnull %local), !dbg !51
  ...

After LICM

  ...
  while.body:                                       ; preds = %while.cond
    %tobool1.not = icmp eq i32 %if_cond, 0, !dbg !34
    br i1 %tobool1.not, label %if.else, label %if.then, !dbg !37
  
  if.then:                                          ; preds = %while.body
    %2 = load i32, i32* @a, align 4, !dbg !38, !tbaa !26
    call void @llvm.dbg.assign(metadata i32 %2, metadata !19, metadata !DIExpression(), metadata !40, metadata i32* %local, metadata !DIExpression()), !dbg !21
    br label %if.end, !dbg !41
  
  if.else:                                          ; preds = %while.body
    %3 = load i32, i32* @b, align 4, !dbg !42, !tbaa !26
    call void @llvm.dbg.assign(metadata i32 %3, metadata !19, metadata !DIExpression(), metadata !40, metadata i32* %local, metadata !DIExpression()), !dbg !21
    tail call void @_Z3escPi(i32* noundef nonnull @a), !dbg !44
    br label %if.end
  
  if.end:                                           ; preds = %if.else, %if.then
    %4 = phi i32 [ %3, %if.else ], [ %2, %if.then ]
    br label %while.cond, !dbg !31, !llvm.loop !45
  
  ; Exit blocks
  while.end:                                        ; preds = %while.cond
    %.lcssa = phi i32 [ %1, %while.cond ]
    store i32 %.lcssa, i32* %local, align 1, !dbg !48, !tbaa !26, !DIAssignID !40
    call void @_Z3escPi(i32* noundef nonnull %local), !dbg !49
  ...


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D133313/new/

https://reviews.llvm.org/D133313

Files:
  llvm/lib/Transforms/Scalar/LICM.cpp
  llvm/test/DebugInfo/Generic/assignment-tracking/licm/merge.ll
  llvm/test/DebugInfo/Generic/assignment-tracking/licm/multi-exit.ll

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