http://gcc.gnu.org/ml/gcc-patches/2007-06/msg01043.html
(This is with the SVN version of GCC and the -mrecip / rsqrt patch by Uros on x86_64-unknown-linux-gnu.) I don't know whether this a bug in the patch [for rsqrt] or only revealed by the patch, but the "aermod.f90" benchmark from Polyhedron [http://www.polyhedron.co.uk/pb05/polyhedron_benchmark_suite.html] crashes here at run time (segmentation fault) when compiled with gfortran -ffast-math -mrecip aermod.f90 Valgrind claims: ==16734== Conditional jump or move depends on uninitialised value(s) ==16734== at 0x4BA046: numrise_ (aermod.f90:35497) ==16734== by 0x4CBC05: prmdelh_ (aermod.f90:39786) ==16734== by 0x41D06F: prmcalc_ (aermod.f90:6787) [...] The program does not crash without -mrecip. - - - Uros answered: http://gcc.gnu.org/ml/gcc-patches/2007-06/msg01044.html gdb points to the top of: Dump of assembler code from 0x808a193 to 0x808a293: 0x0808a193 <numrise_+8963>: mov 0xffffaf8c(%ebp,%edx,4),%eax 0x0808a19a <numrise_+8970>: mov %eax,0xfffffffc(%ebx,%ecx,4) 0x0808a19e <numrise_+8974>: mov 0xffff616c(%ebp,%edx,4),%eax 0x0808a1a5 <numrise_+8981>: mov 0x2c(%ebp),%edx 0x0808a1a8 <numrise_+8984>: mov %eax,0xfffffffc(%edx,%ecx,4) 0x0808a1ac <numrise_+8988>: add $0x1,%ecx where %ebp points to zt. It looks that %edx (that has value of 12324 at the point of crash) got out of bounds. Index into the array (JN (int) = RN (float)) is calculated from DELN variable, that is computed using rcpss. DELN is equal to 4107.55908 in rcpss case and RN is 12325.6777. Perhaps the problem is, that index is constructed from FP variable? [...] Hm, I was referring to this part of numrise function: ! --- Use sliding step-size to sample nearfield more frequently DELN = 2.*FLOAT(NN-NTR)/FLOAT(NTR*(NTR-1)) RN = 0.0 DO IN = 1 , NTR - 1 RN = RN + 1.0 + (IN-1)*DELN JN = RN XTR(IN) = XT(JN) YTR(IN) = YT(JN) ZTR(IN) = ZT(JN) RTR(IN) = RT(JN) ENDDO - - - Note: valgrind shows now error for the version without -mrecip With -mrecip and -bounds-check, one has: At line 35436 of file aermod.f90 Fortran runtime error: Array reference out of bounds for array 'xt', lower bound of dimension 1 exceeded This is SUBROUTINE NUMRISE: DO IN = NBEG , NEND ! --- Define coordinates of plume relative to bldg.-defined origin XBB = XT(IN-1) - XBADJ No such error without bounds check. -- Summary: Crash (out of bounds) with converting real to integer array index with -mrecip Product: gcc Version: 4.3.0 Status: UNCONFIRMED Keywords: wrong-code Severity: normal Priority: P3 Component: fortran AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: burnus at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32352
