[Bug fortran/19693] New: optimization problem with LAPACK routine cgtts2.f

["billingd at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

With gfortran 20050129 I get a testsuite failure at -O2 that I don't see at -
O0.  The failure is in the CGT tests in ctest.in:

 CGT:  General tridiagonal
 Matrix types (1-6 have specified condition numbers):
    1. Diagonal                        7. Random, unspecified CNDNUM
    2. Random, CNDNUM = 2              8. First column zero
    3. Random, CNDNUM = sqrt(0.1/EPS)  9. Last column zero
    4. Random, CNDNUM = 0.1/EPS       10. Last n/2 columns zero
    5. Scaled near underflow          11. Scaled near underflow
    6. Scaled near overflow           12. Scaled near overflow
 Test ratios:
    1: norm( L * U - A )  / ( N * norm(A) * EPS )
    2: norm( B - A * X )  / ( norm(A) * norm(X) * EPS )
    3: norm( X - XACT )   / ( norm(XACT) * CNDNUM * EPS )
    4: norm( X - XACT )   / ( norm(XACT) * CNDNUM * EPS ), refined
    5: norm( X - XACT )   / ( norm(XACT) * (error bound) )
    6: (backward error)   / EPS
    7: RCOND * CNDNUM - 1.0
 Messages:
 NORM ='O', N =    1,           type  5, test( 7) =  0.16777E+08
 NORM ='I', N =    1,           type  5, test( 7) =  0.16777E+08
 TRANS='N', N =    1, NRHS=  1, type  5, test( 3) = 

I have reduced it to the miscompilation of routine cgtts2.f at -O2.  I have 
isolated a single failing case, but if I try to change the routine the problem 
evaporates.

Attached is:
 - driv.f: a small driver program
 - cgtts2.f: the LAPACK routine with the problem.

To reproduce:

gfortran -o pass.exe -O0 driv.f cgtts2.f
gfortran -o fail.exe -O0 driv.f cgtts2.f
./pass
 B(1,1) =  ( 4.0564819E+31,  0.000000    )

./fail
At line 15 of file driv.f
Internal Error: printf is broken
 B(1,1) =  (

Note:  The internal error is PR 19363

-- 
           Summary: optimization problem with LAPACK routine cgtts2.f
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: billingd at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-cygwin
  GCC host triplet: i686-pc-cygwin
GCC target triplet: i686-pc-cygwin


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19693