On Sat, Aug 8, 2009 at 2:59 PM, Sriraman Tallam <tmsri...@google.com> wrote: > Hi, > > Here is a patch to eliminate redundant zero-extension instructions > on x86_64. > > Tested: Ran the gcc regresssion testsuite on x86_64-linux and verified > that the results are the same with/without this patch. > > > Problem Description : > --------------------------------- > > This pass is intended to be applicable only to targets that implicitly > zero-extend 64-bit registers after writing to their lower 32-bit half. > For instance, x86_64 zero-extends the upper bits of a register > implicitly whenever an instruction writes to its lower 32-bit half. > For example, the instruction *add edi,eax* also zero-extends the upper > 32-bits of rax after doing the addition. These zero extensions come > for free and GCC does not always exploit this well. That is, it has > been observed that there are plenty of cases where GCC explicitly > zero-extends registers for x86_64 that are actually useless because > these registers were already implicitly zero-extended in a prior > instruction. This pass tries to eliminate such useless zero extension > instructions. >
Does this fix: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17387 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34653 -- H.J.
