[Committed, PR69058] Don't parallelize loops if libgomp not supported

[Tom de Vries <Tom_deVries at mentor dot com>]

Hi,

when doing an ftree-parallelize-loops=2 build (PR68967), I ran into an 
ICE building libgo.

The ICE can be reproduced using a regular toolchain using this command:
...
$ gccgo src/libgo/go/strconv/decimal.go -O2 -ftree-parallelize-loops=2 -S
...

The problem is that parloops is trying to use libgomp builtins, while 
they're not available.

This patch fixes the ICE by doing an early-out in parloops if the 
libgomp builtins are not available.

Bootstrapped and reg-tested on x86_64.

Committed to trunk.

Thanks,
- Tom

Don't parallelize loops if libgomp not supported

2016-01-07  Tom de Vries  <tom@codesourcery.com>

	PR tree-optimization/69058
	* tree-parloops.c (pass_parallelize_loops::execute): Return 0 if libgomp
	not supported.

---
 gcc/tree-parloops.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gcc/tree-parloops.c b/gcc/tree-parloops.c
index 5bd9c06..e05cc47 100644
--- a/gcc/tree-parloops.c
+++ b/gcc/tree-parloops.c
@@ -2836,6 +2836,10 @@ pass_parallelize_loops::execute (function *fun)
   if (number_of_loops (fun) <= 1)
     return 0;
 
+  tree nthreads = builtin_decl_explicit (BUILT_IN_OMP_GET_NUM_THREADS);
+  if (nthreads == NULL_TREE)
+    return 0;
+
   if (parallelize_loops ())
     {
       fun->curr_properties &= ~(PROP_gimple_eomp);