------- Comment #14 from mkuvyrkov at gcc dot gnu dot org 2010-04-13 20:01 ------- (In reply to comment #10) > - D.1850_209 = -alt_90; > - D.2093_151 = -alb_86; > - D.1849_208 = D.1848_207 - alb_86; > + D.2093_151 = -alt_90; > + D.1849_208 = D.1848_207 - alt_90; > D.1851_210 = D.1849_208 + -1.0e+0; > - z1a_211 = D.1851_210 + D.1850_209; > + D.2094_497 = -alb_86; > + z1a_211 = D.1851_210 - alb_86; > > this doesn't look like an identity transform. You have to be careful with > non-single use vars and make sure they do not end up on a reassociation > chain.
Though it does look fishy, this transformation is OK. In fact, the compiler oscillates a couple of times between using `-alb_86' and `-alt_90'. E.g., the "before" compiler does the following transformation during reassoc1: == - D.1849_208 = D.1848_207 - alb_86; + D.2045_228 = -alb_86; + D.1850_209 = -alt_90; + D.1849_208 = D.1848_207 + D.1850_209; == -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43716
