On Fri, Aug 15, 2014 at 03:45:33PM +0400, Yuri Rumyantsev wrote: > gcc/ChangeLog > 2014-08-15 Yuri Rumyantsev <ysrum...@gmail.com> > > PR target/62011 > * config/i386/i386-protos.h (ix86_avoid_false_dep_for_bm): New function > prototype. > * config/i386/i386.c (ix86_avoid_false_dep_for_bm): New function. > * config/i386/i386.h (TARGET_AVOID_FALSE_DEP_FOR_BM) New macros. > * config/i386/i386.md (ctz<mode>2, clz<mode>2_lzcnt, popcount<mode>2, > *popcount<mode>2_cmp, *popcountsi2_cmp_zext): Output zeroing > destination register for unary bit-manipulation instructions > if required. > * config/i386/x86-tune.def (X86_TUNE_AVOID_FALSE_DEP_FOR_BM): New.
--- config/i386/i386.md (revision 213842) +++ config/i386/i386.md (working copy) @@ -12111,7 +12111,13 @@ "" { if (TARGET_BMI) - return "tzcnt{<imodesuffix>}\t{%1, %0|%0, %1}"; + { + if (ix86_avoid_false_dep_for_bm (insn, operands)) + return "xor{<imodesuffix>}\t%0, %0\n\t" + "tzcnt{<imodesuffix>}\t{%1, %0|%0, %1}"; + else + return "tzcnt{<imodesuffix>}\t{%1, %0|%0, %1}"; + } else if (optimize_function_for_size_p (cfun)) ; else if (TARGET_GENERIC) etc., this will make lenght attribute incorrect though. Jakub