On Fri, Oct 30, 2015 at 5:19 PM, Ian Romanick <i...@freedesktop.org> wrote: > On 10/29/2015 05:52 PM, Matt Turner wrote: >> If we add a new file type, we'd like to get warnings if it's not >> handled. >> >> Unfortuately, gcc seems to have bugs (see the XXX). > > Did you submit a GCC bug?
I did some research and found https://gcc.gnu.org/bugzilla/show_bug.cgi?id=28236 https://gcc.gnu.org/ml/gcc/2007-01/msg01183.html If I understand correctly, an enum can be /any/ integral value in C and that gcc would have to emit extra code to clamp the subject of the switch to ensure that it was an enum value. In C++, however, enums are fully different types and out-of-range values for enums result in undefined behavior. Seems like the compiler should be able to recognize this. In practice, I found that moving the unreachable() into the switch and returning an arbitrary value both shuts up the compiler *and* generates smaller code. gcc *is* smart enough to recognize that the code after the switch is unreachable in that case and avoid emitting instructions for the useless return. How silly. I've modified the patch locally to do that. The relevant hunks now look like: diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp index 2d0acb9..5ab8c15 100644 --- a/src/mesa/drivers/dri/i965/brw_fs.cpp +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp @@ -845,9 +843,8 @@ fs_inst::regs_read(int arg) const REG_SIZE); case MRF: unreachable("MRF registers are not allowed as sources"); - default: - unreachable("Invalid register file"); } + return 0; } bool diff --git a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp index 58bd23f..e207a77 100644 --- a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp +++ b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp @@ -42,9 +42,13 @@ static uint32_t brw_file_from_reg(fs_reg *reg) return BRW_MESSAGE_REGISTER_FILE; case IMM: return BRW_IMMEDIATE_VALUE; - default: + case BAD_FILE: + case HW_REG: + case ATTR: + case UNIFORM: unreachable("not reached"); } + return 0; } _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
