Fix impGetNodeAddr flag handling for volatile, unaligned, and initclass accesses

[Copilot]

impGetNodeAddr returns GTF_IND_COPYABLE_FLAGS (volatile, unaligned, nonfaulting, initclass) from the original access, but five call sites were ignoring these flags, potentially leading to incorrect semantics for volatile/unaligned/initclass operations.

Changes:

• Added allowConfiguredDerefs parameter to impGetNodeAddr: When false, indirections with volatile, unaligned, or initclass flags fall through to temp creation instead of returning the address directly. Defaults to true for backward compatibility.

• Return buffers (3 sites): Set allowConfiguredDerefs = false when obtaining addresses for return buffer arguments passed to helpers. VM helpers cannot handle addresses with volatile, unaligned, or initclass flags.

• Struct field access on instance: Combine flags from impGetNodeAddr with prefix flags when creating the field indirection:

  GenTreeFlags objAddrFlags = GTF_EMPTY;
  obj = impGetNodeAddr(obj, CHECK_SPILL_ALL, &objAddrFlags);
  indirFlags |= objAddrFlags;  // Combine with prefix flags

• Box-isinst optimization: Transfer flags to the hasValue field indirection:

  objToBox = impGetNodeAddr(objToBox, CHECK_SPILL_ALL, &indirFlags);
  impPushOnStack(gtNewIndir(TYP_UBYTE, objToBox, indirFlags), ...);

• Fixed recursive call: Preserve allowConfiguredDerefs in GT_COMMA case to maintain semantics through comma expressions.

All five TODO-Bug?: verify if flags matter here comments resolved.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Review usages of impGetNodeAddr with ignored flags</issue_title>
<issue_description>#85562 made impGetNodeAddr return flags the original access would use. Places that use the API but ignore the returned flags have been marked with // TODO-Bug?: verify if flags matter here.
All such cases should be reviewed and either documented to be fine or fixed to not ignore the flags.
cc @SingleAccretion </issue_description>

<agent_instructions>For uses that end up indirecting the address, simply transfer the flags on to that indirection.
For uses that do not indirect (e.g. passing the address to a VM helper), add a new argument to impGetNodeAddr about whether volatile and unaligned addresses should be allowed, and if not, fall through to the case that copies to a local.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@ Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch See info in [area-owners.md](https://github.com/dotnet/runtime/blob/main/docs/area-owners.md) if you want to be subscribed.

Issue Details

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#85562 made impGetNodeAddr return flags the original access would use. Places that use the API but ignore the returned flags have been marked with // TODO-Bug?: verify if flags matter here.
All such cases should be reviewed and either documented to be fine or fixed to not ignore the flags.
cc @SingleAccretion

Author:	MichalPetryka
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

• Fixes Review usages of impGetNodeAddr with ignored flags #89372

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[jakobbotsch]

@copilot On second thought this needs to check GTF_IND_INITCLASS as well. Can you rename allowVolatileUnaligned to allowConfiguredDerefs at the same time.

[Copilot]

Done in commit 7c2aedd. The parameter is now renamed to allowConfiguredDerefs and the check now includes GTF_IND_INITCLASS in addition to volatile and unaligned flags.