http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52861
Bug #: 52861 Summary: (missed optimisation) missed transformation to memset with -O3 Classification: Unclassified Product: gcc Version: 4.7.0 Status: UNCONFIRMED Severity: minor Priority: P3 Component: fortran AssignedTo: unassig...@gcc.gnu.org ReportedBy: arnau...@users.sourceforge.net This is a minor missed-optimisation noticed as follow up to PR52835. This is not a regression. >cat qq1.f SUBROUTINE QQ2( ISU, ZSPM, RSV, MS ) INTEGER :: ISU(MS) CHARACTER(8) :: ZSPM(MS) REAL :: RSV(MS) DO IS=1,MS ISU(IS)=0 ZSPM(IS)=' ' RSV(IS) =0.0 ENDDO END subroutine qq2 >cat qq2.f SUBROUTINE QQ2( ISU, ZSPM, RSV, MS ) INTEGER :: ISU(MS) CHARACTER(8) :: ZSPM(MS) REAL :: RSV(MS) DO IS=1,MS ISU(IS)=0 RSV(IS) =0.0 ENDDO DO IS=1,MS ZSPM(IS)=' ' ENDDO END subroutine qq2 >gfortran470 -O3 -c qq1.f ; gfortran470 -O3 -c qq2.f >nm qq1.o qq2.o qq1.o: 0000000000000000 T qq2_ qq2.o: U memset 0000000000000000 T qq2_ The compiler has not be able to transform the assignments to ISU and RSV as calls to memset when the loop contains an assignment to a CHARACTER variable. This suggests that the dependency generator can be improved or that the Fortran front-end could pass a better representation to the middle-end. Additionally, it should be possible to transform DO IS=1,MS ZSPM(IS)=' ' ENDDO as a call to memset. gcc 4.7.0 cannot: >cat qq3.f SUBROUTINE QQ2( ZSPM, MS ) CHARACTER(8) :: ZSPM(MS) DO IS=1,MS ZSPM(IS)=' ' ENDDO END subroutine qq2 >/usr/local/gcc/gfortran470 -O3 -c qq3.f >nm qq3 qq3.f qq3.o >nm qq3.o 0000000000000000 T qq2_