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Re-instate "StackPromotion: Ignore unreachable blocks in post-dominator tree."

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With a bug fix which should ensure that it doesn't violate the stack nesting.

Original commit: 3d050f7b43
This commit is contained in:
Erik Eckstein
2016-04-08 09:45:03 -07:00
parent 6cdfc2e469
commit 1eab8aa955
2 changed files with 250 additions and 26 deletions
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199
lib/SILOptimizer/Transforms/StackPromotion.cpp
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@@ -17,6 +17,9 @@
#include "swift/SILOptimizer/Analysis/DominanceAnalysis.h"
#include "swift/SIL/SILArgument.h"
#include "swift/SIL/SILBuilder.h"
#include "swift/SIL/CFG.h"
#include "llvm/Support/GenericDomTree.h"
#include "llvm/Support/GenericDomTreeConstruction.h"
#include "llvm/ADT/Statistic.h"
STATISTIC(NumStackPromoted, "Number of objects promoted to the stack");
@@ -48,9 +51,23 @@ class StackPromoter {
SILFunction *F;
EscapeAnalysis::ConnectionGraph *ConGraph;
DominanceInfo *DT;
PostDominanceInfo *PDT;
EscapeAnalysis *EA;
// We use our own post-dominator tree instead of PostDominatorAnalysis,
// because we ignore unreachable blocks (actually all unreachable sub-graphs).
// Example:
// |
// bb1
// / \
// unreachable bb2
// \
//
// We want to get bb2 as immediate post-domiator of bb1. This is not the case
// with the regualar post-dominator tree.
llvm::DominatorTreeBase<SILBasicBlock> PostDomTree;
bool PostDomTreeValid;
// Pseudo-functions for (de-)allocating array buffers on the stack.
SILFunction *BufferAllocFunc = nullptr;
@@ -120,16 +137,31 @@ class StackPromoter {
SILInstruction *&AllocInsertionPoint,
SILInstruction *&DeallocInsertionPoint);
/// Returns the place where to insert the deallocation.
/// Returns null if this doesn't succeed or, in case \p RestartPoint is set,
/// a new iteration should be triggered.
SILInstruction *findDeallocPoint(SILInstruction *StartInst,
SILInstruction *&RestartPoint,
EscapeAnalysis::CGNode *Node,
int NumUsePointsToFind);
bool strictlyDominates(SILBasicBlock *A, SILBasicBlock *B) {
return A != B && DT->dominates(A, B);
}
bool strictlyPostDominates(SILBasicBlock *A, SILBasicBlock *B) {
return A != B && PDT->dominates(A, B);
calculatePostDomTree();
return A != B && PostDomTree.dominates(A, B);
}
bool postDominates(SILBasicBlock *A, SILBasicBlock *B) {
calculatePostDomTree();
return PostDomTree.dominates(A, B);
}
SILBasicBlock *getImmediatePostDom(SILBasicBlock *BB) {
auto *Node = PDT->getNode(BB);
calculatePostDomTree();
auto *Node = PostDomTree.getNode(BB);
if (!Node)
return nullptr;
auto *IDomNode = Node->getIDom();
@@ -137,13 +169,22 @@ class StackPromoter {
return nullptr;
return IDomNode->getBlock();
}
void calculatePostDomTree() {
if (!PostDomTreeValid) {
// The StackPromoter acts as a "graph" for which the post-dominator-tree
// is calculated.
PostDomTree.recalculate(*this);
PostDomTreeValid = true;
}
}
public:
StackPromoter(SILFunction *F, EscapeAnalysis::ConnectionGraph *ConGraph,
DominanceInfo *DT, PostDominanceInfo *PDT,
EscapeAnalysis *EA) :
F(F), ConGraph(ConGraph), DT(DT), PDT(PDT), EA(EA) { }
DominanceInfo *DT, EscapeAnalysis *EA) :
F(F), ConGraph(ConGraph), DT(DT), EA(EA), PostDomTree(true),
PostDomTreeValid(false) { }
/// What did the optimization change?
enum class ChangeState {
@@ -152,6 +193,8 @@ public:
Calls
};
SILFunction *getFunction() const { return F; }
/// The main entry point for the optimization.
ChangeState promote();
};
@@ -284,6 +327,87 @@ SILFunction *StackPromoter::getBufferDeallocFunc(SILFunction *OrigFunc,
return BufferDeallocFunc;
}
namespace {
/// Iterator which iterates over all basic blocks of a function which are not
/// terminated by an unreachable inst.
class NonUnreachableBlockIter :
public std::iterator<std::forward_iterator_tag, SILBasicBlock, ptrdiff_t> {
SILFunction::iterator BaseIterator;
SILFunction::iterator End;
void skipUnreachables() {
while (true) {
if (BaseIterator == End)
return;
if (!isa<UnreachableInst>(BaseIterator->getTerminator()))
return;
BaseIterator++;
}
}
public:
NonUnreachableBlockIter(SILFunction::iterator BaseIterator,
SILFunction::iterator End) :
BaseIterator(BaseIterator), End(End) {
skipUnreachables();
}
NonUnreachableBlockIter() = default;
SILBasicBlock &operator*() const { return *BaseIterator; }
SILBasicBlock &operator->() const { return *BaseIterator; }
NonUnreachableBlockIter &operator++() {
BaseIterator++;
skipUnreachables();
return *this;
}
NonUnreachableBlockIter operator++(int unused) {
NonUnreachableBlockIter Copy = *this;
++*this;
return Copy;
}
friend bool operator==(NonUnreachableBlockIter lhs,
NonUnreachableBlockIter rhs) {
return lhs.BaseIterator == rhs.BaseIterator;
}
friend bool operator!=(NonUnreachableBlockIter lhs,
NonUnreachableBlockIter rhs) {
return !(lhs == rhs);
}
};
}
namespace llvm {
/// Use the StackPromoter as a wrapper for the function. It holds the list of
/// basic blocks excluding all unreachable blocks.
template <> struct GraphTraits<StackPromoter *>
: public GraphTraits<swift::SILBasicBlock*> {
typedef StackPromoter *GraphType;
static NodeType *getEntryNode(GraphType SP) {
return &SP->getFunction()->front();
}
typedef NonUnreachableBlockIter nodes_iterator;
static nodes_iterator nodes_begin(GraphType SP) {
return nodes_iterator(SP->getFunction()->begin(), SP->getFunction()->end());
}
static nodes_iterator nodes_end(GraphType SP) {
return nodes_iterator(SP->getFunction()->end(), SP->getFunction()->end());
}
static unsigned size(GraphType SP) {
return std::distance(nodes_begin(SP), nodes_end(SP));
}
};
}
bool StackPromoter::canPromoteAlloc(SILInstruction *AI,
SILInstruction *&AllocInsertionPoint,
SILInstruction *&DeallocInsertionPoint) {
@@ -311,13 +435,42 @@ bool StackPromoter::canPromoteAlloc(SILInstruction *AI,
return false;
}
// Try to find the point where to insert the deallocation.
// This might need more than one try in case we need to move the allocation
// out of a stack-alloc-dealloc pair. See findDeallocPoint().
SILInstruction *StartInst = AI;
for (;;) {
SILInstruction *RestartPoint = nullptr;
DeallocInsertionPoint = findDeallocPoint(StartInst, RestartPoint, Node,
NumUsePointsToFind);
if (DeallocInsertionPoint)
return true;
if (!RestartPoint)
return false;
// Moving a buffer allocation call is not trivial because we would need to
// move all the parameter calculations as well. So we just don't do it.
if (!isa<AllocRefInst>(AI))
return false;
// Retry with moving the allocation up.
AllocInsertionPoint = RestartPoint;
StartInst = RestartPoint;
}
}
SILInstruction *StackPromoter::findDeallocPoint(SILInstruction *StartInst,
SILInstruction *&RestartPoint,
EscapeAnalysis::CGNode *Node,
int NumUsePointsToFind) {
// In the following we check two requirements for stack promotion:
// 1) Are all uses in the same control region as the alloc? E.g. if the
// allocation is in a loop then there may not be any uses of the object
// outside the loop.
// 2) We need to find an insertion place for the deallocation so that it
// preserves a properly nested stack allocation-deallocation structure.
SILBasicBlock *StartBlock = AI->getParent();
SILBasicBlock *StartBlock = StartInst->getParent();
// The block where we assume we can insert the deallocation.
SILBasicBlock *EndBlock = StartBlock;
@@ -336,7 +489,7 @@ bool StackPromoter::canPromoteAlloc(SILInstruction *AI,
if (BB == StartBlock) {
// In the first block we start at the allocation instruction and not at
// the begin of the block.
Iter = AI->getIterator();
Iter = StartInst->getIterator();
} else {
// Track all uses in the block arguments.
for (SILArgument *BBArg : BB->getBBArgs()) {
@@ -359,7 +512,7 @@ bool StackPromoter::canPromoteAlloc(SILInstruction *AI,
while (!strictlyPostDominates(EndBlock, Pred)) {
EndBlock = getImmediatePostDom(EndBlock);
if (!EndBlock)
return false;
return nullptr;
}
}
Iter = BB->begin();
@@ -370,8 +523,7 @@ bool StackPromoter::canPromoteAlloc(SILInstruction *AI,
SILInstruction &I = *Iter++;
if (BB == EndBlock && StackDepth == 0 && NumUsePointsToFind == 0) {
// We found a place to insert the stack deallocation.
DeallocInsertionPoint = &I;
return true;
return &I;
}
if (I.isAllocatingStack()) {
StackDepth++;
@@ -388,16 +540,17 @@ bool StackPromoter::canPromoteAlloc(SILInstruction *AI,
//
// In this case we can move the alloc_ref before the alloc_stack
// to fix the nesting.
if (!isa<AllocRefInst>(AI))
return false;
auto *Alloc = dyn_cast<SILInstruction>(I.getOperand(0));
if (!Alloc)
return false;
return nullptr;
// This should always be the case, but let's be on the safe side.
if (!PDT->dominates(StartBlock, Alloc->getParent()))
return false;
AllocInsertionPoint = Alloc;
StackDepth++;
if (!postDominates(StartBlock, Alloc->getParent()))
return nullptr;
// Trigger another iteration with a new start point;
RestartPoint = Alloc;
return nullptr;
}
StackDepth--;
}
@@ -422,7 +575,7 @@ bool StackPromoter::canPromoteAlloc(SILInstruction *AI,
// dealloc_stack %1 // this is the new EndBlock
EndBlock = getImmediatePostDom(EndBlock);
if (!EndBlock)
return false;
return nullptr;
}
// Again, it's important that the EndBlock is the first in the WorkList.
WorkList.insert(EndBlock, -1);
@@ -441,7 +594,7 @@ bool StackPromoter::canPromoteAlloc(SILInstruction *AI,
// cond_br ..., loop, exit
// exit:
// use(%container)
return false;
return nullptr;
}
WorkList.insert(Succ, StackDepth);
}
@@ -466,20 +619,18 @@ private:
auto *EA = PM->getAnalysis<EscapeAnalysis>();
auto *DA = PM->getAnalysis<DominanceAnalysis>();
auto *PDA = PM->getAnalysis<PostDominanceAnalysis>();
SILFunction *F = getFunction();
if (auto *ConGraph = EA->getConnectionGraph(F)) {
StackPromoter promoter(F, ConGraph, DA->get(F), PDA->get(F), EA);
StackPromoter promoter(F, ConGraph, DA->get(F), EA);
switch (promoter.promote()) {
case StackPromoter::ChangeState::None:
break;
case StackPromoter::ChangeState::Insts:
invalidateAnalysis(SILAnalysis::InvalidationKind::Instructions);
break;
case StackPromoter::ChangeState::Calls: {
case StackPromoter::ChangeState::Calls:
invalidateAnalysis(SILAnalysis::InvalidationKind::CallsAndInstructions);
}
break;
}
}