------- Comment #11 from jakub at gcc dot gnu dot org 2009-02-09 20:36 ------- Sure, but in your testcase you do the operation that requires the register while the register var is still in scope and live. The compiler doesn't have a possibility to compile it right. But, if we say it is ok for the compiler to move an unrelated 1 << somevar or call, stringop etc. into a block where the register var is live and ICE because the compiler did it, we'd basically forbid all uses of register vars. Automatic register vars are there mainly to support inline asm hardcoded inputs/outputs for which you don't have special register classes, programmers using them know very well the limitations and that they only copy prepared stuff from other variables into the register variables, do inline asm and copy back the results from local register vars to other vars.
-- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39139
