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JIT: run local struct to field update in morph both pre and post order for returns #75304

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Sep 13, 2022
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JIT: run local struct to field update in morph both pre and post order for returns #75304

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JIT: run local assertion prop before morphing return of local struct …
AndyAyersMS Sep 8, 2022
217140d
revise to try the update pre and post with ap in between
AndyAyersMS Sep 9, 2022
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12 changes: 12 additions & 0 deletions src/coreclr/jit/morph.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -10243,6 +10243,18 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac, bool* optA
{
op1 = fgMorphRetInd(tree->AsUnOp());
}
// Local assertions may enable zero or copy prop.
//
if (fgGlobalMorph && optLocalAssertionProp && (optAssertionCount > 0) && op1->OperIs(GT_LCL_VAR))
{
GenTree* newOp1 = op1;
while (newOp1 != nullptr)
{
op1 = newOp1;
newOp1 = optAssertionProp(apFull, newOp1, nullptr, nullptr);
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It would feel like a lesser evil to "retry" replacing the local with its promoted field in post-order to me. It would be more in line with how the other decomposition transforms work.

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I agree it seems like a more natural fit.

I had a version that did that, but it caused LSRA churn (though not too much).

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I had a version that did that, but it caused LSRA churn (though not too much).

It seems a bit surprising it did -- wouldn't the lack of this replacement cause the failure (assert) being fixed?

To be clear, I meant trying the replacement on both pre- and post- order.

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Yes, I was trying it both places. I'll revive that version....

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Looks like my earlier assessment was wrong; doing the update both pre and post order works nicely and has no diffs on win x64 or x86.

Updated.

}
assert(op1 != nullptr);
}
if (op1->OperIs(GT_LCL_VAR))
{
// With a `genReturnBB` this `RETURN(src)` tree will be replaced by a `ASG(genReturnLocal, src)`
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