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On Mon, Mar 10, 2014 at 11:27 AM, Uros Bizjak <ubizjak@gmail.com> wrote: >>> > Well, better is non-obvious, while it is smaller (which is good for >>> > initialization and thus rarely executed code), the common case is that >>> > *jcr_list is 0 (gcj is used rarely these days) and for the common case it is >>> > one instruction longer. >>> > Perhaps at least use if (__builtin_expect (*jcr_list != NULL, 0))? >>> > Otherwise looks good to me. >>> >>> Following source: >>> >>> void frame_dummy (void) >>> { >>> void **jcr_list = __JCR_LIST__; >>> if (__builtin_expect (*jcr_list != 0, 0)) >>> register_classes (jcr_list); >>> } >>> >>> generates exactly the same code while avoiding the warning. So, >>> following your concern, I am testing following patch: >> >> But then the asm is gone and it can start to break any time soon. >> For GCC __JCR_LIST__ is simply a zero sized local array and thus >> dereferencing it's first element is invalid. It doesn't know that we use >> linker magic to populate the array. > > OK, then we have to live with additional instruction (which isn't bad > either, since the r/i compare can be fused with the cjump, where m/i > compare can't be). > > I will bootstrap/regtest with additional __built_expect. Attached patch is what I plan to commit to mainline soon. Ian, does it look OK to you? 2014-03-10 Uros Bizjak <ubizjak@gmail.com> * crtstuff.c (frame_dummy): Use void **jcr_list temporary variable to avoid array subscript is above array bounds warnings. Use __builtin_expect when checking *jcr_list for NULL. Re-bootstrapped and regression tested on x86_64-pc-linux-gnu {,-m32} and alpha-linux-gnu. Jakub, is it OK for mainline from RMs POV? Shall we backport this patch to other release branches? Uros.
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