Ian Lance Taylor - Re: Null pointer check elimination (original) (raw)

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• From: Ian Lance Taylor
• To: David Daney
• Cc: Anthony Green , java at gcc dot gnu dot org, Diego Novillo , GCC Mailing List
• Date: 11 Nov 2005 22:53:50 -0800
• Subject: Re: Null pointer check elimination
• References: 1131747852.3205.105.camel@localhost.localdomain<4375835F.6070106@avtrex.com>

David Daney ddaney@avtrex.com writes:

Eventually we should manually mark certain function DECLs as not-returning-null instead of my kludgy test for this one case. I don't know if/when I can get to that. Perhaps somebody else can take it from here.

Looks like all the bits in struct tree_common are used up.

Q: Would it make sense to add a flag to struct tree_decl_common to indicate !zero, set it using an attribute, (and automatically in the java front-end for the cases above), and then test for it in tree-vrp.c similar to below?

This should be done using an attribute, yes. If this is going to be tested frequently enough, it would make sense to add a bit to struct tree_function_decl (I don't see any reason to put it in struct tree_decl-common) (there is currently room for one more bit in tree_function_decl on a machine which requires 16-bit alignment, or 17 more bits on a machine which requires 32-bit alignment). Note that it is also possible to simply store the attribute on DECL_ATTRIBUTES and look it up using lookup_attribute.

Ian

• Follow-Ups:
  • Re: Null pointer check elimination
    * From: Diego Novillo
  • Re: Null pointer check elimination
    * From: Daniel Berlin
• References:
  • Re: Null pointer check elimination
    * From: David Daney