http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52890
Bug #: 52890 Summary: Revision 185336 causes 10% degradation on cpu2000 benchmark 252.eon Classification: Unclassified Product: gcc Version: 4.8.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: middle-end AssignedTo: unassig...@gcc.gnu.org ReportedBy: pthau...@gcc.gnu.org CC: berg...@gcc.gnu.org, mjam...@suse.cz Host: powerpc64-linux Target: powerpc64-linux Build: powerpc64-linux Following testcase extracted from benchmark file mrXZRectangle.cc. $ cat test.cc // g++ -m64 -O2 -mcpu=power7 -S test.cc class ggVector3 { public: ggVector3() {e[0] = 1.0; e[1] = e[2] = 0.0; } ggVector3(double e0, double e1, double e2) { e[0] = e0; e[1] = e1; e[2] = e2; } double e[3]; }; class ggONB3 { public: ggONB3() { } ggONB3(const ggVector3& a, const ggVector3& b, const ggVector3& c) { U = a; V = b; W = c; } private: ggVector3 U,V,W; }; class mrViewingHitRecord { public: ggONB3 UVW; }; void foo(mrViewingHitRecord& VHR) { VHR.UVW = ggONB3(ggVector3 (1, 0, 0), ggVector3 (0, 0, -1), ggVector3 (0, 1, 0)); } Revision 185335 produces tight sequence of 8-byte stores: stfd 0,8(3) stfd 0,16(3) stfd 0,24(3) stfd 0,32(3) ... Revision 185336, with additional check for SLOW_UNALIGNED_ACCESS now causes path through store_bit_field() which generates a much larger sequence of byte stores. stb 8,0(3) stb 10,1(3) stb 9,2(3) stb 9,3(3) stb 9,4(3) stb 9,5(3) ...