GCC 6.3 stack increased when using c++ exception compare to 4.9

Hi,

We try to upgrade our gcc 4.9 to gcc 6.3 and we observed that the stack usage is increased compare to 4.9 Here a small code that represent the problem.

#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <stdexcept>

class TContractException: public std::logic_error
{
public:
 TContractException(std::string, unsigned int, std::string, std::string msg) : logic_error(msg.c_str())
 {

 }
 ~TContractException() throw ()
 {
 }
};

class PostconditionException: public TContractException
{
public:
 PostconditionException(std::string a , unsigned int b , std::string c): TContractException(a, b, c, "ERRORPOSTCONDITION")
 {

 }
};

int main(int argc, char* argv[])
{
 (void) argv;
 try
 {
  if(argc == 4) throw "My exception";
  if(argc == 5) throw PostconditionException("test throw contract", 1, "");
 }
 catch(PostconditionException &e)
 {
  printf("exception %s\n", e.what());
 }
 catch(...)
 {
  printf("exception");
 }
}

This is trivial code to show the problem. Compiling this code with 4.9 the first few asm line show that the stack reservation is 36 bytes

:../src/main.cpp **** int main(int argc, char* argv[])
  35:../src/main.cpp **** {
 490 .loc 2 35 0
 491 .cfi_startproc
 492 .cfi_personality 0,__gxx_personality_v0
 493 .cfi_lsda 0,.LLSDA785
 494 @ args = 0, pretend = 0, frame = 32
 495 @ frame_needed = 1, uses_anonymous_args = 0
 496 0000 F0B5 push {r4, r5, r6, r7, lr}
 497 .save {r4, r5, r6, r7, lr}
 498 .cfi_def_cfa_offset 20
 499 .cfi_offset 4, -20
 500 .cfi_offset 5, -16
 501 .cfi_offset 6, -12
 502 .cfi_offset 7, -8
 503 .cfi_offset 14, -4
 504 .pad #36
 505 0002 89B0 sub sp, sp, #36 <--------------------
 506 .cfi_def_cfa_offset 56
 507 .setfp r7, sp, #0
 508 0004 00AF add r7, sp, #0
 509 .cfi_def_cfa_register 7
 510 0006 7860 str r0, [r7, #4]
 511 0008 3960 str r1, [r7]
 512 .LBB7:

But if i compile the same program with gcc 6.3 I got this asm lines

34:../src/main.cpp **** int main(int argc, char* argv[])
  35:../src/main.cpp **** {
 421 .loc 2 35 0
 422 .cfi_startproc
 423 .cfi_personality 0,__gxx_personality_v0
 424 .cfi_lsda 0,.LLSDA893
 425 @ args = 0, pretend = 0, frame = 72
 426 @ frame_needed = 1, uses_anonymous_args = 0
 427 0000 F0B5 push {r4, r5, r6, r7, lr}
 428 .save {r4, r5, r6, r7, lr}
 429 .cfi_def_cfa_offset 20
 430 .cfi_offset 4, -20
 431 .cfi_offset 5, -16
 432 .cfi_offset 6, -12
 433 .cfi_offset 7, -8
 434 .cfi_offset 14, -4
 435 .pad #76
 436 0002 93B0 sub sp, sp, #76 <---------------- More bytes allocated ????
 437 .cfi_def_cfa_offset 96
 438 .setfp r7, sp, #0
 439 0004 00AF add r7, sp, #0
 440 .cfi_def_cfa_register 7
 441 0006 7860 str r0, [r7, #4]
 442 0008 3960 str r1, [r7]

I would like to have an explanation about this. If we have more exception type, the problem is worst.

regards

Jonathan