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ARCSequenceOpts: Add LoopSummary verifier (#33810)

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ARCSequenceOpts with loop support works on regions inside out.
While processing an outer region, it uses summary from
the inner loop region to compute RefCountState transitions used for
CodeMotionSafe optimization.

We do not compute the loop summary by iterating over it twice or
iterating until a fixed point is reached.
Instead loop summary is just a list of refcount effecting instructions.
And BottomUpRefCountState::updateForDifferentLoopInst and
TopDownRefCountState::updateForDifferentLoopInst are used to compute the
RefCountState transition when processing the inner loop region. These
functions are very conservative and the flow sensitive nature of the
summarized instructions do no matter.
This PR adds a verifying assert to confirm this.
This commit is contained in:
Meghana Gupta
2020-09-15 09:27:37 -07:00
committed by GitHub
parent b96eb1d6a4
commit 581f611195
3 changed files with 47 additions and 0 deletions
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8
lib/SILOptimizer/ARC/RefCountState.cpp
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@@ -493,6 +493,8 @@ void BottomUpRefCountState::checkAndResetKnownSafety(
clearKnownSafe();
}
// This function is conservative enough that the flow sensitive nature of
// loop summarized instructions does not matter.
void BottomUpRefCountState::updateForDifferentLoopInst(SILInstruction *I,
AliasAnalysis *AA) {
// If we are not tracking anything, bail.
@@ -500,6 +502,8 @@ void BottomUpRefCountState::updateForDifferentLoopInst(SILInstruction *I,
return;
if (valueCanBeGuaranteedUsedGivenLatticeState()) {
// Any instruction that may need guaranteed use or may decrement the
// refcount will turn off CodeMotionSafety
if (mayGuaranteedUseValue(I, getRCRoot(), AA) ||
mayDecrementRefCount(I, getRCRoot(), AA)) {
LLVM_DEBUG(llvm::dbgs() << " Found potential guaranteed use:\n "
@@ -917,12 +921,16 @@ void TopDownRefCountState::checkAndResetKnownSafety(
clearKnownSafe();
}
// This function is conservative enough that the flow sensitive nature of
// loop summarized instructions does not matter.
void TopDownRefCountState::updateForDifferentLoopInst(SILInstruction *I,
AliasAnalysis *AA) {
// If we are not tracking anything, bail.
if (!isTrackingRefCount())
return;
// Any instruction that may need guaranteed use or may decrement the
// refcount will turn off CodeMotionSafety
if (valueCanBeGuaranteedUsedGivenLatticeState()) {
if (mayGuaranteedUseValue(I, getRCRoot(), AA) ||
mayDecrementRefCount(I, getRCRoot(), AA)) {