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JIT: Stop propagating BBF_SPLIT_FLAGS from inlinee's parent #77600

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Oct 29, 2022
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JIT: Stop propagating BBF_SPLIT_FLAGS from inlinee's parent #77600

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27 changes: 5 additions & 22 deletions src/coreclr/jit/fginline.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -194,14 +194,12 @@ class SubstitutePlaceholdersAndDevirtualizeWalker : public GenTreeVisitor<Substi
// Skip through chains of GT_RET_EXPRs (say from nested inlines)
// to the actual tree to use.
//
BasicBlock* prevInlineeBB = nullptr;
BasicBlock* inlineeBB = nullptr;
GenTree* inlineCandidate = tree;
do
{
GenTreeRetExpr* retExpr = inlineCandidate->AsRetExpr();
inlineCandidate = retExpr->gtSubstExpr;
prevInlineeBB = inlineeBB;
inlineeBB = retExpr->gtSubstBB;
} while (inlineCandidate->OperIs(GT_RET_EXPR));

Expand Down Expand Up @@ -242,34 +240,19 @@ class SubstitutePlaceholdersAndDevirtualizeWalker : public GenTreeVisitor<Substi
*use = inlineCandidate;
m_madeChanges = true;

// TODO-Inlining: The inliner had strange previous behavior where
// it for successful inlines that were chains would propagate the
// flags from the second-to-last inlinee's BB. Remove this once we
// can take these changes. We still need to propagate the mandatory
// "IR-presence" flags.
// Furthermore, we should really only propagate BBF_COPY_PROPAGATE
// TODO-Inlining: We should really only propagate BBF_COPY_PROPAGATE
// flags here. BBF_SPLIT_GAINED includes BBF_PROF_WEIGHT, and
// propagating that has the effect that inlining a tree from a hot
// block into a block without profile weights means we suddenly
// start to see the inliner block as hot and treat future inline
// candidates more aggressively.
//
BasicBlockFlags newBBFlags = BBF_EMPTY;
if (prevInlineeBB != nullptr)
if (inlineeBB != nullptr)
{
newBBFlags |= prevInlineeBB->bbFlags;

if (inlineeBB != nullptr)
{
newBBFlags |= inlineeBB->bbFlags & BBF_COPY_PROPAGATE;
}
// IR may potentially contain nodes that requires mandatory BB flags to be set.
// Propagate those flags from the containing BB.
m_compiler->compCurBB->bbFlags |= inlineeBB->bbFlags & BBF_SPLIT_GAINED;
}
else if (inlineeBB != nullptr)
{
newBBFlags |= inlineeBB->bbFlags;
}

m_compiler->compCurBB->bbFlags |= (newBBFlags & BBF_SPLIT_GAINED);

#ifdef DEBUG
if (m_compiler->verbose)
Expand Down