replica
/
hanchenye-llvm-project
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

[DebugInfo] Improve dbg preservation in LSR. 

Use SCEV to salvage additional @llvm.dbg.value that have turned into
referencing undef after transformation (and traditional
salvageDebugInfo). Before transformation compute SCEV for each
@llvm.dbg.value in the loop body and store it (along side its current
DIExpression). After transformation update those @llvm.dbg.value now
referencing undef by comparing its stored SCEV to the SCEV of the
current loop-header PHI-nodes. Allow match with offset by inserting
compensation code in the DIExpression.

Includes fix for the nullptr deref that caused the original commit
to be reverted in 9d63029770.

Fixes : PR38815

Differential Revision: https://reviews.llvm.org/D87494
This commit is contained in:
Markus Lavin 2020-10-08 12:49:51 +02:00
parent 1e75668821
commit 06758c6a61
4 changed files with 141 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
llvm/include/llvm/Analysis/ScalarEvolution.h
View File

@ -1117,6 +1117,15 @@ public:
const SCEV *S, const Loop *L,
SmallPtrSetImpl<const SCEVPredicate *> &Preds);
/// Compute \p LHS - \p RHS and returns the result as an APInt if it is a
/// constant, and None if it isn't.
///
/// This is intended to be a cheaper version of getMinusSCEV. We can be
/// frugal here since we just bail out of actually constructing and
/// canonicalizing an expression in the cases where the result isn't going
/// to be a constant.
Optional<APInt> computeConstantDifference(const SCEV *LHS, const SCEV *RHS);
private:
/// A CallbackVH to arrange for ScalarEvolution to be notified whenever a
/// Value is deleted.
@ -1799,15 +1808,6 @@ private:
bool splitBinaryAdd(const SCEV *Expr, const SCEV *&L, const SCEV *&R,
SCEV::NoWrapFlags &Flags);
/// Compute \p LHS - \p RHS and returns the result as an APInt if it is a
/// constant, and None if it isn't.
///
/// This is intended to be a cheaper version of getMinusSCEV. We can be
/// frugal here since we just bail out of actually constructing and
/// canonicalizing an expression in the cases where the result isn't going
/// to be a constant.
Optional<APInt> computeConstantDifference(const SCEV *LHS, const SCEV *RHS);
/// Drop memoized information computed for S.
void forgetMemoizedResults(const SCEV *S);

57
llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
View File

@ -59,6 +59,7 @@
#include "llvm/ADT/Hashing.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetOperations.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallBitVector.h"
#include "llvm/ADT/SmallPtrSet.h"
@ -80,6 +81,7 @@
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/GlobalValue.h"
@ -5776,6 +5778,27 @@ static bool ReduceLoopStrength(Loop *L, IVUsers &IU, ScalarEvolution &SE,
if (MSSA)
MSSAU = std::make_unique<MemorySSAUpdater>(MSSA);
// Debug preservation - record all llvm.dbg.value from the loop as well as
// the SCEV of their variable location. Since salvageDebugInfo may change the
// DIExpression we need to store the original here as well (i.e. it needs to
// be in sync with the SCEV).
SmallVector<
std::tuple<DbgValueInst *, const Type *, const SCEV *, DIExpression *>,
32>
DbgValues;
for (auto &B : L->getBlocks()) {
for (auto &I : *B) {
if (DbgValueInst *D = dyn_cast<DbgValueInst>(&I)) {
auto V = D->getVariableLocation();
if (!V || !SE.isSCEVable(V->getType()))
continue;
auto DS = SE.getSCEV(V);
DbgValues.push_back(
std::make_tuple(D, V->getType(), DS, D->getExpression()));
}
}
}
// Run the main LSR transformation.
Changed |=
LSRInstance(L, IU, SE, DT, LI, TTI, AC, TLI, MSSAU.get()).getChanged();
@ -5797,6 +5820,40 @@ static bool ReduceLoopStrength(Loop *L, IVUsers &IU, ScalarEvolution &SE,
DeleteDeadPHIs(L->getHeader(), &TLI, MSSAU.get());
}
}
// Debug preservation - go through all recorded llvm.dbg.value and for those
// that now have an undef variable location use the recorded SCEV to try and
// update it. Compare with SCEV of Phi-nodes of loop header to find a
// suitable update candidate. SCEV match with constant offset is allowed and
// will be compensated for in the DIExpression.
if (Changed) {
for (auto &D : DbgValues) {
auto DbgValue = std::get<DbgValueInst *>(D);
auto DbgValueType = std::get<const Type *>(D);
auto DbgValueSCEV = std::get<const SCEV *>(D);
auto DbgDIExpr = std::get<DIExpression *>(D);
if (!isa<UndefValue>(DbgValue->getVariableLocation()))
continue;
for (PHINode &Phi : L->getHeader()->phis()) {
if (DbgValueType != Phi.getType())
continue;
if (!SE.isSCEVable(Phi.getType()))
continue;
auto PhiSCEV = SE.getSCEV(&Phi);
if (Optional<APInt> Offset =
SE.computeConstantDifference(DbgValueSCEV, PhiSCEV)) {
auto &Ctx = DbgValue->getContext();
DbgValue->setOperand(
0, MetadataAsValue::get(Ctx, ValueAsMetadata::get(&Phi)));
if (Offset.getValue().getSExtValue()) {
SmallVector<uint64_t, 8> Ops;
DIExpression::appendOffset(Ops, Offset.getValue().getSExtValue());
DbgDIExpr = DIExpression::prependOpcodes(DbgDIExpr, Ops, true);
}
DbgValue->setOperand(2, MetadataAsValue::get(Ctx, DbgDIExpr));
}
}
}
}
return Changed;
}

2
llvm/test/DebugInfo/COFF/fpo-shrink-wrap.ll
View File

@ -33,7 +33,7 @@
; ASM: popl %ebx
; ASM: [[EPILOGUE]]: # %return
; ASM: retl $8
; ASM: Ltmp10:
; ASM: Ltmp11:
; ASM: .cv_fpo_endproc
; Note how RvaStart advances 7 bytes to skip the shrink-wrapped portion.

74
llvm/test/Transforms/LoopStrengthReduce/dbg-preserve-0.ll Normal file
View File

@ -0,0 +1,74 @@
; RUN: opt < %s -loop-reduce -S | FileCheck %s
; Test that LSR preserves debug-info for induction variables.
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
define dso_local void @foo(i8* nocapture %p) local_unnamed_addr !dbg !7 {
; CHECK-LABEL: @foo(
entry:
call void @llvm.dbg.value(metadata i8* %p, metadata !13, metadata !DIExpression()), !dbg !16
call void @llvm.dbg.value(metadata i8 0, metadata !14, metadata !DIExpression()), !dbg !17
br label %for.body, !dbg !18
for.cond.cleanup: ; preds = %for.body
ret void, !dbg !19
for.body: ; preds = %entry, %for.body
; CHECK-LABEL: for.body:
%i.06 = phi i8 [ 0, %entry ], [ %inc, %for.body ]
%p.addr.05 = phi i8* [ %p, %entry ], [ %add.ptr, %for.body ]
call void @llvm.dbg.value(metadata i8 %i.06, metadata !14, metadata !DIExpression()), !dbg !17
call void @llvm.dbg.value(metadata i8* %p.addr.05, metadata !13, metadata !DIExpression()), !dbg !16
; CHECK-NOT: call void @llvm.dbg.value(metadata i8* undef
; CHECK: call void @llvm.dbg.value(metadata i8* %lsr.iv, metadata ![[MID_p:[0-9]+]], metadata !DIExpression(DW_OP_constu, 3, DW_OP_minus, DW_OP_stack_value)), !dbg !16
%add.ptr = getelementptr inbounds i8, i8* %p.addr.05, i64 3, !dbg !20
call void @llvm.dbg.value(metadata i8* %add.ptr, metadata !13, metadata !DIExpression()), !dbg !16
; CHECK-NOT: call void @llvm.dbg.value(metadata i8* undef
; CHECK: call void @llvm.dbg.value(metadata i8* %lsr.iv, metadata ![[MID_p]], metadata !DIExpression()), !dbg !16
store i8 %i.06, i8* %add.ptr, align 1, !dbg !23, !tbaa !24
%inc = add nuw nsw i8 %i.06, 1, !dbg !27
call void @llvm.dbg.value(metadata i8 %inc, metadata !14, metadata !DIExpression()), !dbg !17
%exitcond.not = icmp eq i8 %inc, 32, !dbg !28
br i1 %exitcond.not, label %for.cond.cleanup, label %for.body, !dbg !18, !llvm.loop !29
}
declare void @llvm.dbg.value(metadata, metadata, metadata)
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4, !5}
!llvm.ident = !{!6}
!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 12.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
!1 = !DIFile(filename: "lsrdbg.c", directory: "/")
!2 = !{}
!3 = !{i32 7, !"Dwarf Version", i32 4}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = !{i32 1, !"wchar_size", i32 4}
!6 = !{!"clang version 12.0.0"}
!7 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 2, type: !8, scopeLine: 2, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !12)
!8 = !DISubroutineType(types: !9)
!9 = !{null, !10}
!10 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !11, size: 64)
!11 = !DIBasicType(name: "unsigned char", size: 8, encoding: DW_ATE_unsigned_char)
!12 = !{!13, !14}
!13 = !DILocalVariable(name: "p", arg: 1, scope: !7, file: !1, line: 2, type: !10)
; CHECK: ![[MID_p]] = !DILocalVariable(name: "p", arg: 1, scope: !7, file: !1, line: 2, type: !10)
!14 = !DILocalVariable(name: "i", scope: !15, file: !1, line: 4, type: !11)
!15 = distinct !DILexicalBlock(scope: !7, file: !1, line: 4, column: 3)
!16 = !DILocation(line: 0, scope: !7)
!17 = !DILocation(line: 0, scope: !15)
!18 = !DILocation(line: 4, column: 3, scope: !15)
!19 = !DILocation(line: 8, column: 1, scope: !7)
!20 = !DILocation(line: 5, column: 7, scope: !21)
!21 = distinct !DILexicalBlock(scope: !22, file: !1, line: 4, column: 42)
!22 = distinct !DILexicalBlock(scope: !15, file: !1, line: 4, column: 3)
!23 = !DILocation(line: 6, column: 8, scope: !21)
!24 = !{!25, !25, i64 0}
!25 = !{!"omnipotent char", !26, i64 0}
!26 = !{!"Simple C/C++ TBAA"}
!27 = !DILocation(line: 4, column: 38, scope: !22)
!28 = !DILocation(line: 4, column: 31, scope: !22)
!29 = distinct !{!29, !18, !30, !31}
!30 = !DILocation(line: 7, column: 3, scope: !15)
!31 = !{!"llvm.loop.unroll.disable"}