Re: [PATCH] PR c/104506: Tolerate error_mark_node in useless_type_conversion_p.

[Richard Biener <richard.guenther@gmail.com>]

On Mon, Feb 14, 2022 at 1:54 PM Roger Sayle <roger@nextmovesoftware.com> wrote:
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> This simple fix to the middle-end, resolves PR c/104506, by adding an
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> explicit check for error_mark_node to useless_type_conversion_p.  I first
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> trying fixing this in the C front-end, but the type is valid at the point
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> that the NOP_EXPR is created, so the poisoned type leaks to the middle-end.

Hmm, IMHO "fixing" something to error_mark after it has possibly be used
looks broken.

I don't like trying to paper over this in useless_type_conversion_p, the
predicate should not be called on an error_mark_node type.

Alternatively we might want to create an error_type_node that is at least
a type (with main variant error_type_node and TREE_CODE ERROR_TYPE, etc.).
But likely more complicated than avoiding to mess with the type of 'x' after
the fact?

Richard.

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> Returning either true or false from useless_type_conversion_p avoids the
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> ICE-after-error.  Apologies to Andrew Pinski, I hadn't noticed that he'd
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> assigned this PR to himself until after my regression testing had finished.
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> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap and
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> make -k check with no new failures.  Ok for mainline?
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> 2022-02-14  Roger Sayle  <roger@nextmovesoftware.com>
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> gcc/ChangeLog
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> PR c/104506
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> * gimple-expr.cc (useless_type_conversion_p): Add a check for
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> error_mark_node.
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> gcc/testsuite/ChangeLog
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> PR c/104506
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> * gcc.dg/pr104506.c: New test case.
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> Roger
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> --
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