[Bug c++/80032] New: C++ excessive stack usage (no stack reuse)

[jan.smets at nokia dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80032

            Bug ID: 80032
           Summary: C++ excessive stack usage (no stack reuse)
           Product: gcc
           Version: 6.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jan.smets at nokia dot com
  Target Milestone: ---

Created attachment 40959
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40959&action=edit
testcase

I have a unlucky code pattern that resulted in 10592 bytes stack usage when
built with GCC 6.3, whereas it only used 304 bytes when compiled with GCC 5.4.

gcc-5 (Ubuntu 5.4.1-8ubuntu1) 5.4.1 20170304
gcc (Ubuntu 6.3.0-8ubuntu1) 6.3.0 20170221

Attached is a C-Reduced testcase. If the if() block is repeated multiple times
the stack increases more. Looks as if stack isn't reused.

if() block occurs 
 1x : GCC5:  96 bytes , GCC6:  96 bytes
 2x : GCC5: 112 bytes , GCC6: 176 bytes
10x : GCC5: 112 bytes , GCC6: 688 bytes

Testcase compiled with : -fstack-usage -std=c++11 -O2 -Wall

Using -fstack-reuse=none gives GCC 5 the same stack usage as GCC 6.

I think this is a regression.