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Debug info: Teach SROA how to update debug info for fragmented variables.

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This allows us to generate debug info for extremely advanced code such as

  typedef struct { long int a; int b;} S;

  int foo(S s) {
    return s.b;
  }

which at -O1 on x86_64 is codegen'd into

  define i32 @foo(i64 %s.coerce0, i32 %s.coerce1) #0 {
    ret i32 %s.coerce1, !dbg !24
  }

with this patch we emit the following debug info for this

  TAG_formal_parameter [3]
    AT_location( 0x00000000
                 0x0000000000000000 - 0x0000000000000006: rdi, piece 0x00000008, rsi, piece 0x00000004
                 0x0000000000000006 - 0x0000000000000008: rdi, piece 0x00000008, rax, piece 0x00000004 )
                 AT_name( "s" )
                 AT_decl_file( "/Volumes/Data/llvm/_build.ninja.release/test.c" )

Thanks to chandlerc, dblaikie, and echristo for their feedback on all
previous iterations of this patch!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224739 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Adrian Prantl
2014-12-22 22:26:00 +00:00
parent a834d6a4bb
commit e5ca21a2df
4 changed files with 233 additions and 5 deletions
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31
lib/Transforms/Scalar/SROA.cpp
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@ -953,6 +953,10 @@ class SROA : public FunctionPass {
/// currently in the promotable queue.
SetVector<SelectInst *, SmallVector<SelectInst *, 2>> SpeculatableSelects;
/// Debug intrinsics do not show up as regular uses in the
/// IR. This side-table holds the missing use edges.
DenseMap<AllocaInst *, DbgDeclareInst *> DbgDeclares;
public:
SROA(bool RequiresDomTree = true)
: FunctionPass(ID), RequiresDomTree(RequiresDomTree), C(nullptr),
@ -3230,6 +3234,27 @@ bool SROA::rewritePartition(AllocaInst &AI, AllocaSlices &AS,
new AllocaInst(SliceTy, nullptr, Alignment,
AI.getName() + ".sroa." + Twine(B - AS.begin()), &AI);
++NumNewAllocas;
// Migrate debug information from the old alloca to the new alloca
// and the individial slices.
if (DbgDeclareInst *DbgDecl = DbgDeclares.lookup(&AI)) {
DIVariable Var(DbgDecl->getVariable());
DIExpression Piece;
DIBuilder DIB(*AI.getParent()->getParent()->getParent(),
/*AllowUnresolved*/ false);
// Create a piece expression describing the slice, if the new slize is
// smaller than the old alloca or the old alloca already was described
// with a piece. It would be even better to just compare against the size
// of the type described in the debug info, but then we would need to
// build an expensive DIRefMap.
if (SliceSize < DL->getTypeAllocSize(AI.getAllocatedType()) ||
DIExpression(DbgDecl->getExpression()).isVariablePiece())
Piece = DIB.createPieceExpression(BeginOffset, SliceSize);
Instruction *NewDDI = DIB.insertDeclare(NewAI, Var, Piece, &AI);
NewDDI->setDebugLoc(DbgDecl->getDebugLoc());
DbgDeclares.insert(std::make_pair(NewAI, cast<DbgDeclareInst>(NewDDI)));
DeadInsts.insert(DbgDecl);
}
}
DEBUG(dbgs() << "Rewriting alloca partition "
@ -3680,9 +3705,13 @@ bool SROA::runOnFunction(Function &F) {
BasicBlock &EntryBB = F.getEntryBlock();
for (BasicBlock::iterator I = EntryBB.begin(), E = std::prev(EntryBB.end());
I != E; ++I)
I != E; ++I) {
if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
Worklist.insert(AI);
else if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I))
if (auto AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress()))
DbgDeclares.insert(std::make_pair(AI, DDI));
}
bool Changed = false;
// A set of deleted alloca instruction pointers which should be removed from