[PATCH] D53390: [DebugInfo][Dexter] Unreachable line stepped onto after SimplifyCFG.

[Carlos Alberto Enciso via Phabricator via llvm-commits]

CarlosAlbertoEnciso added inline comments.


================
Comment at: lib/Transforms/Utils/SimplifyCFG.cpp:1379
+  Instruction *InsertPt = BIParent->size() > 1
+                              ? BIParent->getTerminator()->getPrevNode()
+                              : BIParent->getTerminator();
----------------
CarlosAlbertoEnciso wrote:
> vsk wrote:
> > A bit nitty-gritty, but: Can the instruction before the terminator be a debug info intrinsic?
> > 
> > If so, I think the line location you pick be different if you switch from -gline-tables-only versus -g.
> Thanks for your review.
> 
> Changing the test case to:
> 
> ```
> int main() {
>   volatile int foo = 0;
> 
>   int beards = 0;
>   bool cond = foo == 4;
>   if (cond)
>     beards = 8;
>   else
>     beards = 4;
> 
>   volatile bool tmp;
>   volatile bool *face = &tmp;
>   *face = cond;
>  
>   return beards;
> }
> ```
> 
> The IR will look like:
> 
> ```
>   ...
>   %foo.0. = load volatile i32, i32* %foo, align 4, !dbg !28, !tbaa !23
>   %cmp = icmp eq i32 %foo.0., 4, !dbg !28
>   %frombool = zext i1 %cmp to i8, !dbg !28
>   call void @llvm.dbg.value(metadata i8 %frombool, metadata !16, metadata !DIExpression()), !dbg !28
>   br i1 %cmp, label %if.then, label %if.else, !dbg !29
> 
> if.then:                                          ; preds = %entry
>   call void @llvm.dbg.value(metadata i32 8, metadata !15, metadata !DIExpression()), !dbg !27
>   br label %if.end, !dbg !30
> 
> if.else:                                          ; preds = %entry
>   call void @llvm.dbg.value(metadata i32 4, metadata !15, metadata !DIExpression()), !dbg !27
>   br label %if.end
> 
> if.end:                                           ; preds = %if.else, %if.then
> ...
> ```
> 
> The instruction before the terminator is a debug info intrinsic.
> 
> 
> If so, I think the line location you pick be different if you switch from -gline-tables-only versus -g.

IR for '-g'

```
  ...
  %cmp = icmp eq i32 %foo.0., 4, !dbg !26
  %frombool = zext i1 %cmp to i8, !dbg !26
  call void @llvm.dbg.value(metadata i8 %frombool, metadata !16, metadata !DIExpression()), !dbg !26
  br i1 %cmp, label %if.then, label %if.else, !dbg !27
  ...
  !26 = !DILocation(line: 5, scope: !8)
```

IR for '-gline-tables-only'

```
  ...
  %cmp = icmp eq i32 %foo.0., 4, !dbg !15
  %frombool = zext i1 %cmp to i8, !dbg !15
  br i1 %cmp, label %if.then, label %if.else, !dbg !16
  ...
  !15 = !DILocation(line: 5, scope: !8)
  ...
```
InsertPts
```
  call void @llvm.dbg.value(metadata i8 %frombool, metadata !16, metadata !DIExpression()), !dbg !26

&&

  %frombool = zext i1 %cmp to i8, !dbg !15
```

For both options, the line location of the insertion point is the same, debug location `!DILocation(line: 5, scope: !8)`.




https://reviews.llvm.org/D53390