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llvm-6502/test/Transforms/LoopRotate/dbgvalue.ll
Chandler Carruth a403ceb205 [LPM] Fix PR18643, another scary place where loop transforms failed to 
preserve loop simplify of enclosing loops.

The problem here starts with LoopRotation which ends up cloning code out
of the latch into the new preheader it is buidling. This can create
a new edge from the preheader into the exit block of the loop which
breaks LoopSimplify form. The code tries to fix this by splitting the
critical edge between the latch and the exit block to get a new exit
block that only the latch dominates. This sadly isn't sufficient.

The exit block may be an exit block for multiple nested loops. When we
clone an edge from the latch of the inner loop to the new preheader
being built in the outer loop, we create an exiting edge from the outer
loop to this exit block. Despite breaking the LoopSimplify form for the
inner loop, this is fine for the outer loop. However, when we split the
edge from the inner loop to the exit block, we create a new block which
is in neither the inner nor outer loop as the new exit block. This is
a predecessor to the old exit block, and so the split itself takes the
outer loop out of LoopSimplify form. We need to split every edge
entering the exit block from inside a loop nested more deeply than the
exit block in order to preserve all of the loop simplify constraints.

Once we try to do that, a problem with splitting critical edges
surfaces. Previously, we tried a very brute force to update LoopSimplify
form by re-computing it for all exit blocks. We don't need to do this,
and doing this much will sometimes but not always overlap with the
LoopRotate bug fix. Instead, the code needs to specifically handle the
cases which can start to violate LoopSimplify -- they aren't that
common. We need to see if the destination of the split edge was a loop
exit block in simplified form for the loop of the source of the edge.
For this to be true, all the predecessors need to be in the exact same
loop as the source of the edge being split. If the dest block was
originally in this form, we have to split all of the deges back into
this loop to recover it. The old mechanism of doing this was
conservatively correct because at least *one* of the exiting blocks it
rewrote was the DestBB and so the DestBB's predecessors were fixed. But
this is a much more targeted way of doing it. Making it targeted is
important, because ballooning the set of edges touched prevents
LoopRotate from being able to split edges *it* needs to split to
preserve loop simplify in a coherent way -- the critical edge splitting
would sometimes find the other edges in need of splitting but not
others.

Many, *many* thanks for help from Nick reducing these test cases
mightily. And helping lots with the analysis here as this one was quite
tricky to track down.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200393 91177308-0d34-0410-b5e6-96231b3b80d8
2014-01-29 13:16:53 +00:00

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; RUN: opt -S -loop-rotate < %s | FileCheck %s
declare void @llvm.dbg.declare(metadata, metadata) nounwind readnone
declare void @llvm.dbg.value(metadata, i64, metadata) nounwind readnone
define i32 @tak(i32 %x, i32 %y, i32 %z) nounwind ssp {
; CHECK-LABEL: define i32 @tak(
; CHECK: entry
; CHECK-NEXT: call void @llvm.dbg.value(metadata !{i32 %x}
entry:
br label %tailrecurse
tailrecurse: ; preds = %if.then, %entry
%x.tr = phi i32 [ %x, %entry ], [ %call, %if.then ]
%y.tr = phi i32 [ %y, %entry ], [ %call9, %if.then ]
%z.tr = phi i32 [ %z, %entry ], [ %call14, %if.then ]
tail call void @llvm.dbg.value(metadata !{i32 %x.tr}, i64 0, metadata !6), !dbg !7
tail call void @llvm.dbg.value(metadata !{i32 %y.tr}, i64 0, metadata !8), !dbg !9
tail call void @llvm.dbg.value(metadata !{i32 %z.tr}, i64 0, metadata !10), !dbg !11
%cmp = icmp slt i32 %y.tr, %x.tr, !dbg !12
br i1 %cmp, label %if.then, label %if.end, !dbg !12
if.then: ; preds = %tailrecurse
%sub = sub nsw i32 %x.tr, 1, !dbg !14
%call = tail call i32 @tak(i32 %sub, i32 %y.tr, i32 %z.tr), !dbg !14
%sub6 = sub nsw i32 %y.tr, 1, !dbg !14
%call9 = tail call i32 @tak(i32 %sub6, i32 %z.tr, i32 %x.tr), !dbg !14
%sub11 = sub nsw i32 %z.tr, 1, !dbg !14
%call14 = tail call i32 @tak(i32 %sub11, i32 %x.tr, i32 %y.tr), !dbg !14
br label %tailrecurse
if.end: ; preds = %tailrecurse
br label %return, !dbg !16
return: ; preds = %if.end
ret i32 %z.tr, !dbg !17
}
@channelColumns = external global i64
@horzPlane = external global i8*, align 8
define void @FindFreeHorzSeg(i64 %startCol, i64 %row, i64* %rowStart) {
; Ensure that the loop increment basic block is rotated into the tail of the
; body, even though it contains a debug intrinsic call.
; CHECK-LABEL: define void @FindFreeHorzSeg(
; CHECK: %dec = add
; CHECK-NEXT: tail call void @llvm.dbg.value
; CHECK-NEXT: br i1 %tobool, label %for.cond, label %[[LOOP_EXIT:[^,]*]]
; CHECK: [[LOOP_EXIT]]:
; CHECK-NEXT: phi i64 [ %{{[^,]*}}, %{{[^,]*}} ]
; CHECK-NEXT: br label %for.end
entry:
br label %for.cond
for.cond:
%i.0 = phi i64 [ %startCol, %entry ], [ %dec, %for.inc ]
%cmp = icmp eq i64 %i.0, 0
br i1 %cmp, label %for.end, label %for.body
for.body:
%0 = load i64* @channelColumns, align 8
%mul = mul i64 %0, %row
%add = add i64 %mul, %i.0
%1 = load i8** @horzPlane, align 8
%arrayidx = getelementptr inbounds i8* %1, i64 %add
%2 = load i8* %arrayidx, align 1
%tobool = icmp eq i8 %2, 0
br i1 %tobool, label %for.inc, label %for.end
for.inc:
%dec = add i64 %i.0, -1
tail call void @llvm.dbg.value(metadata !{i64 %dec}, i64 0, metadata !{metadata !"undef"})
br label %for.cond
for.end:
%add1 = add i64 %i.0, 1
store i64 %add1, i64* %rowStart, align 8
ret void
}
!llvm.module.flags = !{!20}
!llvm.dbg.sp = !{!0}
!0 = metadata !{i32 589870, metadata !18, metadata !1, metadata !"tak", metadata !"tak", metadata !"", i32 32, metadata !3, i1 false, i1 true, i32 0, i32 0, null, i32 256, i1 false, i32 (i32, i32, i32)* @tak, null, null, null, i32 0} ; [ DW_TAG_subprogram ] [line 32] [def] [scope 0] [tak]
!1 = metadata !{i32 589865, metadata !18} ; [ DW_TAG_file_type ]
!2 = metadata !{i32 589841, metadata !18, i32 12, metadata !"clang version 2.9 (trunk 125492)", i1 true, metadata !"", i32 0, metadata !19, metadata !19, null, null, null, metadata !""} ; [ DW_TAG_compile_unit ]
!3 = metadata !{i32 589845, metadata !18, metadata !1, metadata !"", i32 0, i64 0, i64 0, i32 0, i32 0, null, metadata !4, i32 0, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
!4 = metadata !{metadata !5}
!5 = metadata !{i32 589860, null, metadata !2, metadata !"int", i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ]
!6 = metadata !{i32 590081, metadata !0, metadata !"x", metadata !1, i32 32, metadata !5, i32 0} ; [ DW_TAG_arg_variable ]
!7 = metadata !{i32 32, i32 13, metadata !0, null}
!8 = metadata !{i32 590081, metadata !0, metadata !"y", metadata !1, i32 32, metadata !5, i32 0} ; [ DW_TAG_arg_variable ]
!9 = metadata !{i32 32, i32 20, metadata !0, null}
!10 = metadata !{i32 590081, metadata !0, metadata !"z", metadata !1, i32 32, metadata !5, i32 0} ; [ DW_TAG_arg_variable ]
!11 = metadata !{i32 32, i32 27, metadata !0, null}
!12 = metadata !{i32 33, i32 3, metadata !13, null}
!13 = metadata !{i32 589835, metadata !18, metadata !0, i32 32, i32 30, i32 6} ; [ DW_TAG_lexical_block ]
!14 = metadata !{i32 34, i32 5, metadata !15, null}
!15 = metadata !{i32 589835, metadata !18, metadata !13, i32 33, i32 14, i32 7} ; [ DW_TAG_lexical_block ]
!16 = metadata !{i32 36, i32 3, metadata !13, null}
!17 = metadata !{i32 37, i32 1, metadata !13, null}
!18 = metadata !{metadata !"/Volumes/Lalgate/cj/llvm/projects/llvm-test/SingleSource/Benchmarks/BenchmarkGame/recursive.c", metadata !"/Volumes/Lalgate/cj/D/projects/llvm-test/SingleSource/Benchmarks/BenchmarkGame"}
!19 = metadata !{i32 0}
!20 = metadata !{i32 1, metadata !"Debug Info Version", i32 1}
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