[PATCH, 2/2][PR66642] Add empty loop exit block in transform_to_exit_first_loop_alt

[Tom de Vries]

Hi,

I ran into a failure with parloops for reduction loop testcase 
libgomp/testsuite/libgomp.c/parloops-exit-first-loop-alt-3.c.  When we 
exercise the low iteration count loop, the test-case fails.

To understand the problem, let's first look at what happens when we use 
transform_to_exit_first_loop (the original one) instead of 
transform_to_exit_first_loop_alt (the alternative one, which is 
currently used, and causing the failure).

Before transform_to_exit_first_loop, the low iteration count loop and 
the main loop share the loop exit block. After 
transform_to_exit_first_loop, that's not the case anymore, the main loop 
now has an exit block with a single predecessor. Subsequently, 
separate_decls_in_region inserts code in the main loop exit block, which 
is only triggered upon exit of the main loop.

However, transform_to_exit_first_loop_alt does not insert such an exit 
block, and the code inserted by separate_decls_in_region is also active 
for the low iteration count loop, which results in an incorrect 
reduction result when the low iteration count loop is used.


This patch fixes the problem by making sure 
transform_to_exit_first_loop_alt adds a new exit block inbetween the 
main loop header and the old exit block.


Bootstrapped and reg-tested on x86_64.

OK for trunk?

Thanks,
- Tom
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 0002-Add-empty-loop-exit-block-in-transform_to_exit_first.patch
Type: text/x-patch
Size: 6359 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/gcc-patches/attachments/20150625/5c7e22d7/attachment.bin>