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JIT: fold trees after inline return expression updates #1751

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Feb 1, 2020
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JIT: fold trees after inline return expression updates #1751

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71 changes: 68 additions & 3 deletions src/coreclr/src/jit/flowgraph.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -22309,7 +22309,7 @@ Compiler::fgWalkResult Compiler::fgUpdateInlineReturnExpressionPlaceHolder(GenTr
Compiler* comp = data->compiler;
CORINFO_CLASS_HANDLE retClsHnd = NO_CLASS_HANDLE;

if (tree->OperGet() == GT_RET_EXPR)
while (tree->OperGet() == GT_RET_EXPR)
{
// We are going to copy the tree from the inlinee,
// so record the handle now.
Expand All @@ -22321,8 +22321,15 @@ Compiler::fgWalkResult Compiler::fgUpdateInlineReturnExpressionPlaceHolder(GenTr

// Skip through chains of GT_RET_EXPRs (say from nested inlines)
// to the actual tree to use.
GenTree* inlineCandidate = tree->gtRetExprVal();
var_types retType = tree->TypeGet();
//
// Also we might as well try and fold the return value.
// Eg returns of constant bools will have CASTS.
// This folding may uncover more GT_RET_EXPRs, so we loop around
// until we've got something distinct.
//
GenTree* inlineCandidate = tree->gtRetExprVal();
inlineCandidate = comp->gtFoldExpr(inlineCandidate);
var_types retType = tree->TypeGet();

#ifdef DEBUG
if (comp->verbose)
Expand Down Expand Up @@ -22592,6 +22599,64 @@ Compiler::fgWalkResult Compiler::fgLateDevirtualization(GenTree** pTree, fgWalkD
}
}
}
else if (tree->OperGet() == GT_JTRUE)
{
// See if this jtrue is now foldable.
BasicBlock* block = comp->compCurBB;
GenTree* condTree = tree->AsOp()->gtOp1;
assert(tree == block->lastStmt()->GetRootNode());

if (condTree->OperGet() == GT_CNS_INT)
{
JITDUMP(" ... found foldable jtrue at [%06u] in BB%02u\n", dspTreeID(tree), block->bbNum);
noway_assert((block->bbNext->countOfInEdges() > 0) && (block->bbJumpDest->countOfInEdges() > 0));

// It would be nice to assert that "tree" is side-effect
// free, before we bash it.
//
// But we expect to see the GTF_CALL flag set, because
// this tree is an ancestor of an inline return
// value placeholder, and those always have GTF_CALL set,
// since if inlining fails we'd swap the call back in
// place.
//
// So, check that at least everything else is clear.
assert((tree->gtFlags & (GTF_SIDE_EFFECT & ~GTF_CALL)) == 0);

tree->gtBashToNOP();

BasicBlock* bTaken = nullptr;
BasicBlock* bNotTaken = nullptr;

if (condTree->AsIntCon()->gtIconVal != 0)
{
block->bbJumpKind = BBJ_ALWAYS;
bTaken = block->bbJumpDest;
bNotTaken = block->bbNext;
}
else
{
block->bbJumpKind = BBJ_NONE;
bTaken = block->bbNext;
bNotTaken = block->bbJumpDest;
}

comp->fgRemoveRefPred(bNotTaken, block);

// If that was the last ref, a subsequent flow-opt pass
// will clean up the now-unreachable bNotTaken, and any
// other transitively unreachable blocks.
if (bNotTaken->bbRefs == 0)
{
JITDUMP("... it looks like BB%02u is now unreachable!\n", bNotTaken->bbNum);
}
}
}
else
{
GenTree* foldedTree = comp->gtFoldExpr(tree);
*pTree = foldedTree;
}

return WALK_CONTINUE;
}
Expand Down