https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68550
--- Comment #2 from Joost VandeVondele <Joost.VandeVondele at mat dot ethz.ch> --- The following simpler looking testcase fails at -O1: > cat bug.f90 SUBROUTINE PD2VAL(RES,NDERIV,TG1,TG2,C0) INTEGER, PARAMETER :: dp=8 REAL(KIND=dp), INTENT(OUT) :: res(*) REAL(KIND=dp), INTENT(IN) :: TG1, TG2, C0(105,*) REAL(KIND=dp) :: T1(0:13), T2(0:13) DO K=1,NDERIV+1 RES(K)=RES(K)+DOT_PRODUCT(T1(0:7),C0(70:77,K))*T2(6) RES(K)=RES(K)+DOT_PRODUCT(T1(0:4),C0(91:95,K))*T2(9) RES(K)=RES(K)+DOT_PRODUCT(T1(0:3),C0(96:99,K))*T2(10) ENDDO END SUBROUTINE PD2VAL > gfortran -O1 -fcheck=bounds -floop-nest-optimize bug.f90 bug.f90:1:0: SUBROUTINE PD2VAL(RES,NDERIV,TG1,TG2,C0) Error: missing PHI def val.0_68 = PHI <(4), 0.0(6)> bug.f90:1:0: internal compiler error: verify_gimple failed 0xbad719 verify_gimple_in_cfg(function*, bool) ../../gcc/gcc/tree-cfg.c:5082