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[DebugInfo][RemoveDIs] Instrument loop-deletion for DPValues #73042

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merged 3 commits into from
Nov 23, 2023
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[DebugInfo][RemoveDIs] Instrument loop-deletion for DPValues #73042

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[DebugInfo][RemoveDIs] Instrument loop-deletion for DPValues
jmorse Jun 7, 2023
b40da9f
clang-format
jmorse Nov 23, 2023
6e255fb
Switch to insert-testing a container
jmorse Nov 23, 2023
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35 changes: 32 additions & 3 deletions llvm/lib/Transforms/Utils/LoopUtils.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -604,6 +604,7 @@ void llvm::deleteDeadLoop(Loop *L, DominatorTree *DT, ScalarEvolution *SE,
// Use a map to unique and a vector to guarantee deterministic ordering.
llvm::SmallDenseSet<DebugVariable, 4> DeadDebugSet;
llvm::SmallVector<DbgVariableIntrinsic *, 4> DeadDebugInst;
llvm::SmallVector<DPValue *, 4> DeadDPValues;

if (ExitBlock) {
// Given LCSSA form is satisfied, we should not have users of instructions
Expand All @@ -628,6 +629,24 @@ void llvm::deleteDeadLoop(Loop *L, DominatorTree *DT, ScalarEvolution *SE,
"Unexpected user in reachable block");
U.set(Poison);
}

// RemoveDIs: do the same as below for DPValues.
if (Block->IsNewDbgInfoFormat) {
for (DPValue &DPV :
llvm::make_early_inc_range(I.getDbgValueRange())) {
DebugVariable Key(DPV.getVariable(), DPV.getExpression(),
DPV.getDebugLoc().get());
if (!DeadDebugSet.insert(Key).second)
continue;
// Unlinks the DPV from it's container, for later insertion.
DPV.removeFromParent();
DeadDPValues.push_back(&DPV);
}
}

// For one of each variable encountered, preserve a debug intrinsic (set
// to Poison) and transfer it to the loop exit. This terminates any
// variable locations that were set during the loop.
auto *DVI = dyn_cast<DbgVariableIntrinsic>(&I);
if (!DVI)
continue;
Expand All @@ -642,12 +661,22 @@ void llvm::deleteDeadLoop(Loop *L, DominatorTree *DT, ScalarEvolution *SE,
// be be replaced with undef. Loop invariant values will still be available.
// Move dbg.values out the loop so that earlier location ranges are still
// terminated and loop invariant assignments are preserved.
Instruction *InsertDbgValueBefore = ExitBlock->getFirstNonPHI();
assert(InsertDbgValueBefore &&
DIBuilder DIB(*ExitBlock->getModule());
BasicBlock::iterator InsertDbgValueBefore =
ExitBlock->getFirstInsertionPt();
assert(InsertDbgValueBefore != ExitBlock->end() &&
"There should be a non-PHI instruction in exit block, else these "
"instructions will have no parent.");

for (auto *DVI : DeadDebugInst)
DVI->moveBefore(InsertDbgValueBefore);
DVI->moveBefore(*ExitBlock, InsertDbgValueBefore);

// Due to the "head" bit in BasicBlock::iterator, we're going to insert
// each DPValue right at the start of the block, wheras dbg.values would be
// repeatedly inserted before the first instruction. To replicate this
// behaviour, do it backwards.
for (DPValue *DPV : llvm::reverse(DeadDPValues))
ExitBlock->insertDPValueBefore(DPV, InsertDbgValueBefore);
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It's a shame we have to replicate weirdness. It would be ideal to fix the issue before hand, then apply the DPValue change to a good base. On the other hand, investigating every potential debug-info bug would probably be prohibitive to getting this finished.

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Alas this is inherent in dbg.values having an absolute ordering and us trying to have completely identical outputs -- the reason why this reversal exists is that it can have a meaningful effect on output when building real codebases :(, and we've had to fix it up. This is something we can fix, but as part of a future "what happens when you jam two blocks of debug-info together" refactor.

}

// Remove the block from the reference counting scheme, so that we can
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1 change: 1 addition & 0 deletions llvm/test/Transforms/LoopDeletion/crashbc.ll
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
; Make sure we don't crash when writing bitcode.
; RUN: opt < %s -passes=loop-deletion -o /dev/null
; RUN: opt < %s -passes=loop-deletion -o /dev/null --try-experimental-debuginfo-iterators

define void @f() {
br label %bb1
Expand Down
18 changes: 15 additions & 3 deletions llvm/test/Transforms/LoopDeletion/diundef.ll
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Original file line number Diff line number Diff line change
@@ -1,11 +1,18 @@
; RUN: opt %s -passes=loop-deletion -S | FileCheck %s
; RUN: opt %s -passes=loop-deletion -S | FileCheck %s --implicit-check-not=dbg.value
; RUN: opt %s -passes=loop-deletion -S --try-experimental-debuginfo-iterators | FileCheck %s --implicit-check-not=dbg.value

target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.14.0"

@a = common local_unnamed_addr global i32 0, align 4, !dbg !0

define i32 @b() local_unnamed_addr !dbg !12 {
; CHECK-LABEL: entry
; CHECK: call void @llvm.dbg.value(metadata i32 0, metadata ![[IVAR:[0-9]+]],
; CHECK-LABEL: for.end:
; CHECK-NEXT: call void @llvm.dbg.value(metadata i32 undef, metadata ![[IVAR]], metadata !DIExpression()), !dbg !17
; CHECK-NEXT: call void @llvm.dbg.value(metadata i32 undef, metadata ![[JVAR:[0-9]+]], metadata !DIExpression()), !dbg !17
; CHECK-NEXT: %call = tail call i32 {{.*}} @patatino()
entry:
call void @llvm.dbg.value(metadata i32 0, metadata !16, metadata !DIExpression()), !dbg !17
br label %for.cond, !dbg !18
Expand All @@ -15,11 +22,10 @@ for.cond: ; preds = %for.cond, %entry
call void @llvm.dbg.value(metadata i32 %i.0, metadata !16, metadata !DIExpression()), !dbg !17
%inc = add nuw nsw i32 %i.0, 1, !dbg !21
call void @llvm.dbg.value(metadata i32 %inc, metadata !16, metadata !DIExpression()), !dbg !17
call void @llvm.dbg.value(metadata i32 %inc, metadata !37, metadata !DIExpression()), !dbg !17
%exitcond = icmp ne i32 %inc, 3, !dbg !23
br i1 %exitcond, label %for.cond, label %for.end, !dbg !24, !llvm.loop !25

; CHECK: call void @llvm.dbg.value(metadata i32 undef, metadata !16, metadata !DIExpression()), !dbg !17
; CHECK-NEXT: %call = tail call i32 {{.*}} @patatino()
for.end: ; preds = %for.cond
%call = tail call i32 (...) @patatino() #3, !dbg !27
%0 = load i32, ptr @a, align 4, !dbg !28
Expand All @@ -34,6 +40,11 @@ entry:
ret i32 0, !dbg !36
}

; CHECK: declare void @llvm.dbg.value(metadata,

; CHECK: ![[IVAR]] = !DILocalVariable(name: "i",
; CHECK: ![[JVAR]] = !DILocalVariable(name: "j",

declare void @llvm.dbg.value(metadata, metadata, metadata)

!llvm.dbg.cu = !{!2}
Expand Down Expand Up @@ -73,3 +84,4 @@ declare void @llvm.dbg.value(metadata, metadata, metadata)
!34 = distinct !DISubprogram(name: "main", scope: !3, file: !3, line: 9, type: !13, scopeLine: 9, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !4)
!35 = !DILocation(line: 9, column: 14, scope: !34)
!36 = !DILocation(line: 9, column: 19, scope: !34)
!37 = !DILocalVariable(name: "j", scope: !12, file: !3, line: 3, type: !6)
1 change: 1 addition & 0 deletions llvm/test/Transforms/LoopDeletion/over-defensive-undefing-dbg-values.ll
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
; RUN: opt -S %s -passes=loop-deletion | FileCheck %s
; RUN: opt -S %s -passes=loop-deletion --try-experimental-debuginfo-iterators | FileCheck %s

;; static int foo(int Param) __attribute__((always_inline));
;; static int foo(int Param) { return Param * Param * 2; }
Expand Down