[Bug c/70232] New: excessive stack usage with -O2

["arnd at linaro dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70232

            Bug ID: 70232
           Summary: excessive stack usage with -O2
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: arnd at linaro dot org
  Target Milestone: ---

Created attachment 37964
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37964&action=edit
partially reduced test case

Using gcc-6.0 for building the Linux kernel, I see one file (out of many
hundred randconfig test builds so far) that occasionally hits the maximum
per-function stack size limit. I have only tested on 32-bit ARM, and I have
manually reduced the test case:

$ arm-linux-gnueabi-gcc -o lpfc_scsi.o -O2 -Wframe-larger-than=1024
lpfc_scsi.c: In function 'lpfc_find_next_oas_lun':
lpfc_scsi.c:117:1: warning: the frame size of 1152 bytes is larger than 1024
bytes [-Wframe-larger-than=]
$ arm-linux-gnueabi-gcc --version                                               
arm-linux-gnueabi-gcc (GCC) 6.0.0 20160313 (experimental)

I see this with all options as long as -O2 is set, but not with -O3 or -O1 or
-Os. Normal stack usage for this function is usually 128 bytes.