[DebugInfo@O2][LoopVectorize] pr39024: Vectorized code linenos step through loop even after completion

Summary:
Bug: https://bugs.llvm.org/show_bug.cgi?id=39024

The bug reports that a vectorized loop is stepped through 4 times and each step through the loop seemed to show a different path. I found two problems here:

A) An incorrect line number on a preheader block (for.body.preheader) instruction causes a step into the loop before it begins.
B) Instructions in the middle block have different line numbers which give the impression of another iteration.

In this patch I give all of the middle block instructions the line number of the scalar loop latch terminator branch. This seems to provide the smoothest debugging experience because the vectorized loops will always end on this line before dropping into the scalar loop. To solve problem A I have altered llvm::SplitBlockPredecessors to accommodate loop header blocks.

I have set up a separate review D61933 for a fix which is required for this patch.

Reviewers: samsonov, vsk, aprantl, probinson, anemet, hfinkel, jmorse

Reviewed By: hfinkel, jmorse

Subscribers: jmorse, javed.absar, eraman, kcc, bjope, jmellorcrummey, hfinkel, gbedwell, hiraditya, zzheng, llvm-commits

Tags: #llvm, #debug-info

Differential Revision: https://reviews.llvm.org/D60831

> llvm-svn: 363046

llvm-svn: 363786

1 files changed, 122 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LoopSimplify/do-preheader-dbg.ll b/llvm/test/Transforms/LoopSimplify/do-preheader-dbg.ll
new file mode 100755
index 00000000000..7cacc49cd80
--- /dev/null
+++ b/llvm/test/Transforms/LoopSimplify/do-preheader-dbg.ll
@@ -0,0 +1,122 @@
+; Confirm that the line number for the do.body.preheader block
+; branch is the the start of the loop.
+
+; RUN: opt -simplifycfg -loop-simplify -keep-loops="false" -S <%s | FileCheck %s
+
+; CHECK: do.body.preheader:
+; CHECK-NEXT: phi
+; CHECK-NEXT: phi
+; CHECK-NEXT: br label %do.body, !dbg ![[DL:[0-9]+]]
+; CHECK: ![[DL]] = !DILocation(line: 4,
+
+; This IR can be generated by running:
+; clang src.cpp -O2 -g -S -emit-llvm -mllvm -opt-bisect-limit=62 -o -
+;
+; Where  src.cpp contains:
+; int foo(char *Bytes, int Count)
+; {
+;     int Total = 0;
+;     do
+;         Total += Bytes[--Count];
+;     while (Count);
+;     return Total;
+; }
+
+define dso_local i32 @"foo"(i8* nocapture readonly %Bytes, i32 %Count) local_unnamed_addr !dbg !8 {
+entry:
+  %0 = sext i32 %Count to i64, !dbg !10
+  %min.iters.check = icmp ult i32 %Count, 8, !dbg !10
+  br i1 %min.iters.check, label %do.body.preheader, label %vector.ph, !dbg !10
+
+vector.ph:                                        ; preds = %entry
+  %n.vec = and i64 %0, -8, !dbg !10
+  %ind.end = sub nsw i64 %0, %n.vec, !dbg !10
+  br label %vector.body, !dbg !10
+
+vector.body:                                      ; preds = %vector.body, %vector.ph
+  %index = phi i64 [ 0, %vector.ph ], [ %index.next, %vector.body ]
+  %vec.phi = phi <4 x i32> [ zeroinitializer, %vector.ph ], [ %11, %vector.body ]
+  %vec.phi5 = phi <4 x i32> [ zeroinitializer, %vector.ph ], [ %12, %vector.body ]
+  %1 = xor i64 %index, -1, !dbg !11
+  %2 = add i64 %1, %0, !dbg !11
+  %3 = getelementptr inbounds i8, i8* %Bytes, i64 %2, !dbg !11
+  %4 = getelementptr inbounds i8, i8* %3, i64 -3, !dbg !11
+  %5 = bitcast i8* %4 to <4 x i8>*, !dbg !11
+  %wide.load = load <4 x i8>, <4 x i8>* %5, align 1, !dbg !11, !tbaa !12
+  %reverse = shufflevector <4 x i8> %wide.load, <4 x i8> undef, <4 x i32> <i32 3, i32 2, i32 1, i32 0>, !dbg !11
+  %6 = getelementptr inbounds i8, i8* %3, i64 -4, !dbg !11
+  %7 = getelementptr inbounds i8, i8* %6, i64 -3, !dbg !11
+  %8 = bitcast i8* %7 to <4 x i8>*, !dbg !11
+  %wide.load6 = load <4 x i8>, <4 x i8>* %8, align 1, !dbg !11, !tbaa !12
+  %reverse7 = shufflevector <4 x i8> %wide.load6, <4 x i8> undef, <4 x i32> <i32 3, i32 2, i32 1, i32 0>, !dbg !11
+  %9 = sext <4 x i8> %reverse to <4 x i32>, !dbg !11
+  %10 = sext <4 x i8> %reverse7 to <4 x i32>, !dbg !11
+  %11 = add nsw <4 x i32> %vec.phi, %9, !dbg !11
+  %12 = add nsw <4 x i32> %vec.phi5, %10, !dbg !11
+  %index.next = add i64 %index, 8
+  %13 = icmp eq i64 %index.next, %n.vec
+  br i1 %13, label %middle.block, label %vector.body, !llvm.loop !15
+
+middle.block:                                     ; preds = %vector.body
+  %.lcssa12 = phi <4 x i32> [ %11, %vector.body ], !dbg !11
+  %.lcssa = phi <4 x i32> [ %12, %vector.body ], !dbg !11
+  %bin.rdx = add <4 x i32> %.lcssa, %.lcssa12, !dbg !11
+  %rdx.shuf = shufflevector <4 x i32> %bin.rdx, <4 x i32> undef, <4 x i32> <i32 2, i32 3, i32 undef, i32 undef>, !dbg !11
+  %bin.rdx8 = add <4 x i32> %bin.rdx, %rdx.shuf, !dbg !11
+  %rdx.shuf9 = shufflevector <4 x i32> %bin.rdx8, <4 x i32> undef, <4 x i32> <i32 1, i32 undef, i32 undef, i32 undef>, !dbg !11
+  %bin.rdx10 = add <4 x i32> %bin.rdx8, %rdx.shuf9, !dbg !11
+  %14 = extractelement <4 x i32> %bin.rdx10, i32 0, !dbg !11
+  %cmp.n = icmp eq i64 %n.vec, %0
+  br i1 %cmp.n, label %do.end, label %do.body.preheader, !dbg !10
+
+do.body.preheader:                                ; preds = %middle.block, %entry
+  %indvars.iv.ph = phi i64 [ %0, %entry ], [ %ind.end, %middle.block ]
+  %Total.0.ph = phi i32 [ 0, %entry ], [ %14, %middle.block ]
+  br label %do.body, !dbg !11
+
+do.body:                                          ; preds = %do.body.preheader, %do.body
+  %indvars.iv = phi i64 [ %indvars.iv.next, %do.body ], [ %indvars.iv.ph, %do.body.preheader ]
+  %Total.0 = phi i32 [ %add, %do.body ], [ %Total.0.ph, %do.body.preheader ], !dbg !18
+  %indvars.iv.next = add nsw i64 %indvars.iv, -1, !dbg !11
+  %arrayidx = getelementptr inbounds i8, i8* %Bytes, i64 %indvars.iv.next, !dbg !11
+  %15 = load i8, i8* %arrayidx, align 1, !dbg !11, !tbaa !12
+  %conv = sext i8 %15 to i32, !dbg !11
+  %add = add nsw i32 %Total.0, %conv, !dbg !11
+  %16 = icmp eq i64 %indvars.iv.next, 0
+  br i1 %16, label %do.end.loopexit, label %do.body, !dbg !11, !llvm.loop !19
+
+do.end.loopexit:                                  ; preds = %do.body
+  %add.lcssa11 = phi i32 [ %add, %do.body ], !dbg !11
+  br label %do.end, !dbg !21
+
+do.end:                                           ; preds = %do.end.loopexit, %middle.block
+  %add.lcssa = phi i32 [ %14, %middle.block ], [ %add.lcssa11, %do.end.loopexit ], !dbg !11
+  ret i32 %add.lcssa, !dbg !21
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6}
+!llvm.ident = !{!7}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "", isOptimized: true, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "src2.cpp", directory: "")
+!2 = !{}
+!3 = !{i32 2, !"CodeView", i32 1}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 2}
+!6 = !{i32 7, !"PIC Level", i32 2}
+!7 = !{!""}
+!8 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 1, type: !9, scopeLine: 2, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!9 = !DISubroutineType(types: !2)
+!10 = !DILocation(line: 4, scope: !8)
+!11 = !DILocation(line: 5, scope: !8)
+!12 = !{!13, !13, i64 0}
+!13 = !{!"omnipotent char", !14, i64 0}
+!14 = !{!"Simple C++ TBAA"}
+!15 = distinct !{!15, !10, !16, !17}
+!16 = !DILocation(line: 6, scope: !8)
+!17 = !{!"llvm.loop.isvectorized", i32 1}
+!18 = !DILocation(line: 0, scope: !8)
+!19 = distinct !{!19, !10, !16, !20, !17}
+!20 = !{!"llvm.loop.unroll.runtime.disable"}
+!21 = !DILocation(line: 7, scope: !8)