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[Mem2Reg] Replaced loop with getSingleSuccessor. #40020

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Merged
merged 3 commits into from
Nov 11, 2021
Merged

[Mem2Reg] Replaced loop with getSingleSuccessor. #40020

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09dde09
[Mem2Reg] Replaced loop with getSingleSuccessor.
nate-chandler Nov 2, 2021
8af76de
[Test] Added brief comments describing goal.
nate-chandler Nov 2, 2021
ee9d309
[NFC] Added TODO about phi pruning of lifetimes.
nate-chandler Oct 12, 2021
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33 changes: 23 additions & 10 deletions lib/SILOptimizer/Transforms/SILMem2Reg.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -666,6 +666,11 @@ StoreInst *StackAllocationPromoter::promoteAllocationInBlock(
runningVals = beginLexicalLifetimeAfterStore(asi, si);
// Create a use of the newly created copy in order to keep phi pruning
// from deleting our lifetime beginning instructions.
//
// TODO: Remove this hack, it is only necessary because erasePhiArgument
// calls deleteEdgeValue which calls
// deleteTriviallyDeadOperandsOfDeadArgument and deletes the copy
// and borrow that we added and want not to have deleted.
SILBuilderWithScope::insertAfter(
runningVals->value.copy->getDefiningInstruction(),
[&](auto builder) {
Expand Down Expand Up @@ -1665,22 +1670,30 @@ void MemoryToRegisters::removeSingleBlockAllocation(AllocStackInst *asi) {
GraphNodeWorklist<SILBasicBlock *, 2> worklist;
worklist.initialize(parentBlock);
while (auto *block = worklist.pop()) {
assert(domInfo->dominates(parentBlock, block));
auto *terminator = block->getTerminator();
if (isa<UnreachableInst>(terminator)) {
endLexicalLifetimeBeforeInst(asi, /*beforeInstruction=*/terminator, ctx,
runningVals->value);
continue;
}
bool endedLifetime = false;
for (auto *successor : block->getSuccessorBlocks()) {
if (!domInfo->dominates(parentBlock, successor)) {
endLexicalLifetimeBeforeInst(asi, /*beforeInstruction=*/terminator,
ctx, runningVals->value);
endedLifetime = true;
break;
}
}
if (endedLifetime) {
SILBasicBlock *successor = nullptr;
// If any successor is not dominated by the parentBlock, then we must end
// the lifetime before that successor.
//
// Suppose that a successor is not dominated by parentBlock. Recall that
// block _is_ dominated by parentBlock. Thus that successor must have
// more than one predecessor: block, and at least one other. (Otherwise
// it would be dominated by parentBlock contrary to our assumption.)
// Recall that SIL does not allow critical edges. Therefore block has
// only a single successor.
//
// Use the above fact to only look for lack of domination of a successor
// if that successor is the single successor of block.
if ((successor = block->getSingleSuccessorBlock()) &&
(!domInfo->dominates(parentBlock, successor))) {
endLexicalLifetimeBeforeInst(asi, /*beforeInstruction=*/terminator, ctx,
runningVals->value);
continue;
}
for (auto *successor : block->getSuccessorBlocks()) {
Expand Down
11 changes: 7 additions & 4 deletions test/SILOptimizer/mem2reg_lifetime.sil
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Original file line number Diff line number Diff line change
Expand Up @@ -1548,6 +1548,7 @@ entry(%instance : @owned $C):
}


// End lifetime before unreachable inst.
// CHECK-LABEL: sil [ossa] @unreachable_5 : $@convention(thin) (@owned C) -> () {
// CHECK: {{bb[0-9]+}}([[INSTANCE:%[^,]+]] : @owned $C):
// CHECK: [[LIFETIME:%[^,]+]] = begin_borrow [lexical] [[INSTANCE]]
Expand All @@ -1567,6 +1568,7 @@ exit:
unreachable
}

// Bail out if alloc_stack is in unreachable block.
// CHECK-LABEL: sil [ossa] @unreachable_6 : $@convention(thin) (@owned C) -> () {
// CHECK: alloc_stack [lexical]
// CHECK-LABEL: } // end sil function 'unreachable_6'
Expand All @@ -1585,6 +1587,7 @@ exit:
}


// Bail out if alloc_stack is in unreachable block.
// CHECK-LABEL: sil [ossa] @unreachable_7 : $@convention(thin) (@owned C) -> () {
// CHECK: alloc_stack [lexical]
// CHECK-LABEL: } // end sil function 'unreachable_7'
Expand All @@ -1606,7 +1609,7 @@ exit:
return %res : $()
}


// Bail out if alloc_stack is in unreachable block.
// CHECK-LABEL: sil [ossa] @unreachable_8 : $@convention(thin) (@owned C) -> () {
// CHECK: alloc_stack [lexical]
// CHECK-LABEL: } // end sil function 'unreachable_8'
Expand All @@ -1632,7 +1635,7 @@ exit:
return %res : $()
}


// End lifetime after loop which is followed by unreachable.
// CHECK-LABEL: sil [ossa] @unreachable_loop_1 : $@convention(thin) () -> () {
// CHECK: {{bb[0-9]+}}:
// CHECK: [[GET_C:%[^,]+]] = function_ref @getC : $@convention(thin) () -> @owned C
Expand Down Expand Up @@ -1672,7 +1675,7 @@ die:
unreachable
}


// Bail out if alloc_stack is in unreachable block.
// CHECK-LABEL: sil [ossa] @unreachable_loop_2 : $@convention(thin) () -> () {
// CHECK: alloc_stack [lexical]
// CHECK-LABEL: } // end sil function 'unreachable_loop_2'
Expand All @@ -1697,7 +1700,7 @@ die:
unreachable
}


// Bail out if alloc_stack is in unreachable block.
// CHECK-LABEL: sil [ossa] @unreachable_loop_3 : $@convention(thin) () -> () {
// CHECK: alloc_stack [lexical]
// CHECK-LABEL: } // end sil function 'unreachable_loop_3'
Expand Down