[PATCH] D29596: Make MachineBasicBlock::updateTerminator to update DebugLoc as well

[Taewook Oh via Phabricator via llvm-commits]

twoh created this revision.

Currently MachineBasicBlock::updateTerminator simply drops DebugLoc for newly created branch instructions, which may cause incorrect stepping and/or imprecise sample profile data. Below is an example:

   1 extern int bar(int x);
   2
   3 int foo(int *begin, int *end) {
   4   int *i;
   5   int ret = 0;
   6   for (
   7       i = begin ;
   8       i != end ;
   9       i++)
  10   {
  11       ret += bar(*i);
  12   }
  13   return ret;
  14 }

Below is a bitcode of 'foo' at the end of LLVM-IR level optimizations with -O3:

  define i32 @foo(i32* readonly %begin, i32* readnone %end) !dbg !4 {
  entry:
    %cmp6 = icmp eq i32* %begin, %end, !dbg !9
    br i1 %cmp6, label %for.end, label %for.body.preheader, !dbg !12
  
  for.body.preheader:                               ; preds = %entry
    br label %for.body, !dbg !13
  
  for.body:                                         ; preds = %for.body.preheader, %for.body
    %ret.08 = phi i32 [ %add, %for.body ], [ 0, %for.body.preheader ]
    %i.07 = phi i32* [ %incdec.ptr, %for.body ], [ %begin, %for.body.preheader ]
    %0 = load i32, i32* %i.07, align 4, !dbg !13, !tbaa !15
    %call = tail call i32 @bar(i32 %0), !dbg !19
    %add = add nsw i32 %call, %ret.08, !dbg !20
    %incdec.ptr = getelementptr inbounds i32, i32* %i.07, i64 1, !dbg !21
    %cmp = icmp eq i32* %incdec.ptr, %end, !dbg !9
    br i1 %cmp, label %for.end.loopexit, label %for.body, !dbg !12, !llvm.loop !22
  
  for.end.loopexit:                                 ; preds = %for.body
    br label %for.end, !dbg !24
  
  for.end:                                          ; preds = %for.end.loopexit, %entry
    %ret.0.lcssa = phi i32 [ 0, %entry ], [ %add, %for.end.loopexit ]
    ret i32 %ret.0.lcssa, !dbg !24
  }

where

  !12 = !DILocation(line: 6, column: 3, scope: !11)

. As you can see, the terminator of 'entry' block, which is a loop control branch, has a DebugLoc of line 6, column 3. Howerver, after the execution of 'MachineBlock::updateTerminator' function, which is triggered by MachineSinking pass, the DebugLoc info is dropped as below (see there's no debug-location for JNE_1):

  bb.0.entry:
    successors: %bb.4(0x30000000), %bb.1.for.body.preheader(0x50000000)
    liveins: %rdi, %rsi
  
    %6 = COPY %rsi
    %5 = COPY %rdi
    %8 = SUB64rr %5, %6, implicit-def %eflags, debug-location !9
    JNE_1 %bb.1.for.body.preheader, implicit %eflags 

This patch addresses this issue and make newly created branch instructions to keep debug-location info.


https://reviews.llvm.org/D29596

Files:
  lib/CodeGen/MachineBasicBlock.cpp
  test/CodeGen/X86/update-terminator-debugloc.ll

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D29596.87270.patch
Type: text/x-patch
Size: 5323 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20170206/9e0a44b4/attachment.bin>