From 96dea914279283e081ae6dc2be6fdb78a6ee9556 Mon Sep 17 00:00:00 2001
From: noel <ndkeen@lbl.gov>
Date: Mon, 24 Apr 2017 11:36:23 -0700
Subject: [PATCH] Disable FP checks for a certain LAPACK routine, by using
 ieee_exceptions module to turn off FP trapping that is enabled by -fpe0. Only
 for DEBUG builds, only for cori-knl, and only for Intel compiler. Fixes #1183
 [BFB]

---
 .../config/acme/machines/config_compilers.xml |  3 +--
 .../cam/src/physics/clubb/lapack_wrap.F90     | 20 +++++++++++++++++--
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/cime/config/acme/machines/config_compilers.xml b/cime/config/acme/machines/config_compilers.xml
index b9da2ab61ef7..9c9c205be12b 100644
--- a/cime/config/acme/machines/config_compilers.xml
+++ b/cime/config/acme/machines/config_compilers.xml
@@ -596,8 +596,7 @@ for mct, etc.
   <ADD_SLIBS> -L$(NETCDF_DIR) -lnetcdff -Wl,--as-needed,-L$(NETCDF_DIR)/lib -lnetcdff -lnetcdf </ADD_SLIBS>
   <ADD_SLIBS> -mkl -lpthread -lm </ADD_SLIBS>
   <ADD_GPTL_CPPDEFS> -DHAVE_PAPI </ADD_GPTL_CPPDEFS>
-  <ADD_CPPDEFS>  -DHAVE_SLASHPROC </ADD_CPPDEFS>
-  <!--ADD_CPPDEFS>  -DHAVE_NANOTIME -DBIT64 -DHAVE_VPRINTF -DHAVE_BACKTRACE -DHAVE_SLASHPROC -DHAVE_COMM_F2C -DHAVE_TIMES -DHAVE_GETTIMEOFDAY  </ADD_CPPDEFS> -->
+  <ADD_CPPDEFS> -DARCH_MIC_KNL -DHAVE_SLASHPROC </ADD_CPPDEFS>
   <MPIFC> ftn </MPIFC>
   <MPICC> cc </MPICC>
   <MPICXX> CC </MPICXX>
diff --git a/components/cam/src/physics/clubb/lapack_wrap.F90 b/components/cam/src/physics/clubb/lapack_wrap.F90
index f1282703b91b..ac7246d48d15 100644
--- a/components/cam/src/physics/clubb/lapack_wrap.F90
+++ b/components/cam/src/physics/clubb/lapack_wrap.F90
@@ -218,7 +218,11 @@ subroutine tridag_solve &
 
     use clubb_precision, only: &
       core_rknd ! Variable(s)
-
+#ifndef NDEBUG
+#if defined(ARCH_MIC_KNL) && defined(CPRINTEL)
+    use, intrinsic :: ieee_exceptions
+#endif
+#endif
     implicit none
 
     ! External
@@ -268,8 +272,20 @@ subroutine tridag_solve &
 !-----------------------------------------------------------------------
 
     if ( kind( diag(1) ) == dp ) then
-      call dgtsv( ndim, nrhs, subd(2:ndim), diag, supd(1:ndim-1),  & 
+#ifndef NDEBUG
+#if defined(ARCH_MIC_KNL) && defined(CPRINTEL)
+      ! when floating-point exceptions are turned on, this call was failing with a div-by-zero on KNL with Intel/MKL. Solution 
+      ! was to turn off exceptions only here at this call (and only for machine with ARCH_MIC_KNL defined) (github 1183)
+      call ieee_set_halting_mode(IEEE_DIVIDE_BY_ZERO, .false.) ! Turn off stopping on div-by-zero only
+#endif
+#endif
+      call dgtsv( ndim, nrhs, subd(2:ndim), diag, supd(1:ndim-1),  &
                   rhs, ndim, info )
+#ifndef NDEBUG
+#if defined(ARCH_MIC_KNL) && defined(CPRINTEL)
+      call ieee_set_halting_mode(IEEE_DIVIDE_BY_ZERO, .true.) ! Turn back on stopping on div-by-zero only
+#endif
+#endif
 
     else if ( kind( diag(1) ) == sp ) then
       call sgtsv( ndim, nrhs, subd(2:ndim), diag, supd(1:ndim-1),  &