------- Comment #39 from rguenther at suse dot de 2010-01-22 21:47 ------- Subject: Re: [4.5 Regression] stdarg pass produces wrong code
On Fri, 22 Jan 2010, jakub at gcc dot gnu dot org wrote: > ------- Comment #38 from jakub at gcc dot gnu dot org 2010-01-22 19:17 > ------- > In 4.4 the apY = apX; assignment isn't optimized out, because the code after > it > reads from the apY's fields (apY is the struct from the inline, apX in the > caller). But in 4.5 FRE replaces them by whatever is written into apX fields. > It surprises me FRE does this, I'd expect that the struct needs to be SRAed > first before such optimizations can do anything with it. It's a feature ;) FRE can look through struct copies now and thus can value-number x to 1 in s.a = 1; r = s; x = r.a; > That said, other options would be prevent FRE from doing that kind of things > with RECORD_TYPE __builtin_va_list objects in the first fre pass, or for DCE1 > to > somehow signalize to the stdarg pass if it removes an va_list = va_list > assignment that it should just signalize that va_list escapes. or alpha could make the va_list struct copies volatile. Or we can schedule tree-stdarg earlier. Richard. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41089
