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JIT: Account for mixed-enregistered locals when zeroing without block-init #104593

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Jul 10, 2024
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JIT: Account for mixed-enregistered locals when zeroing without block-init #104593

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JIT: Account for mixed-enregistered locals when zeroing without block…
jakobbotsch Jul 9, 2024
ec73237
Tighten assert
jakobbotsch Jul 9, 2024
c9a724f
Remove check
jakobbotsch Jul 9, 2024
1dade32
Oops
jakobbotsch Jul 9, 2024
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17 changes: 9 additions & 8 deletions src/coreclr/jit/codegencommon.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4024,9 +4024,15 @@ void CodeGen::genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg,
continue;
}

// TODO-Review: I'm not sure that we're correctly handling the mustInit case for
// partially-enregistered vars in the case where we don't use a block init.
noway_assert(varDsc->lvIsInReg() || varDsc->lvOnFrame);
// Locals that are (only) in registers to begin with do not need
// their stack home zeroed. Their register will be zeroed later in
// the prolog.
if (varDsc->lvIsInReg() && !varDsc->lvLiveInOutOfHndlr)
{
continue;
}

noway_assert(varDsc->lvOnFrame);
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In genCheckUseBlockInit it looks like the main loop only increases initStkLclCnt when varDsc->lvIsOnFrame.

So couldn't we use that as an early out detection mechanism? Basically:

if (!varDsc->lvMustInit || !varDsc->lvOnFrame)
{
    continue;
}

There's then a secondary handler that increments for spill temps containing pointers, but that looks to be independent of this main loop in genZeroInitFrame and is handled in its own subsequent loop.

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@jakobbotsch jakobbotsch Jul 9, 2024 •
edited
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genCheckUseBlockInit will set lvMustInit, so I don't think we need more checks here... the logic is that if genCheckUseBlockInit left lvMustInit as 1 and it isn't in a register, then it must be on frame as otherwise we wouldn't need to init it.


// lvMustInit can only be set for GC types or TYP_STRUCT types
// or when compInitMem is true
Expand All @@ -4035,11 +4041,6 @@ void CodeGen::genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg,
noway_assert(varTypeIsGC(varDsc->TypeGet()) || (varDsc->TypeGet() == TYP_STRUCT) ||
compiler->info.compInitMem || compiler->opts.compDbgCode);

if (!varDsc->lvOnFrame)
{
continue;
}

if ((varDsc->TypeGet() == TYP_STRUCT) && !compiler->info.compInitMem &&
(varDsc->lvExactSize() >= TARGET_POINTER_SIZE))
{
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