[Bug ipa/66271] New: -Os generates incorrect code on ARM possibly due to IPA

[Bug ipa/66271] New: -Os generates incorrect code on ARM possibly due to IPA

[gccbugs at rooted dot tk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66271

            Bug ID: 66271
           Summary: -Os generates incorrect code on ARM possibly due to
                    IPA
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: ipa
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gccbugs at rooted dot tk
  Target Milestone: ---

Created attachment 35609
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35609&action=edit
code snippet and generated assembly

GCC generates incorrect code when cross compiling for ARM on x86_64 on version
5.1.0 snapshot 5-20150519. The code is correct when -fno-ipa-sra is added as a
switch, making me believe that this is an issue with IPA. This bug breaks
compiling Linux, particularly lib/vsprintf.c.

The problematic part of that file is attached as a code snippet along with the
generated assembly. It was compiled with the following command line:

arm-none-eabi-gcc bug.c -S -o bug.s -Os -Wall -Wextra -fverbose-asm
-frecord-gcc-switches

The issue occurs if spec.field_width is passed in as -1. LDRSH at line 96
correctly sign extends this 16-bit value to the 32-bit value -1. If
!(spec.flags & LEFT), then the branch at line 100 is not taken. The loop does
not run due to the comparison at line 104 (r0 is the result of strnlen(s,
...)). However, lines 103 and 105 effectively zero out the top 16 bits of r3,
which is later written back to r5 at line 114. At line 132, r5 should be -2 or
0xFFFFFFFE but is instead 0x0000FFFE. Thus, the branch at line 136 is not taken
even though it should not be taken ((len < spec.field_width--) should always be
true if spec.field_width is negative and no wrapping occurs). The end result is
that lines 49-51 in the C file run once even when they should not run.

The code would work correctly if LSR were replaced with ASR on lines 105 and
135. This is done correctly at lines 110 and 140, which makes it odd that the
other two lines would be different.

[Bug c/66271] -Os generates incorrect code on ARM possibly due to IPA

[gccbugs at rooted dot tk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66271

--- Comment #1 from gccbugs at rooted dot tk ---
Oddly enough, the code is correct with -O2 instead of -Os.

[Bug c/66271] -Os generates incorrect code on ARM possibly due to IPA

[gccbugs at rooted dot tk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66271

--- Comment #2 from gccbugs at rooted dot tk ---
Created attachment 35610
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35610&action=edit
correct code with -O2

[Bug ipa/66271] -Os generates incorrect code on ARM possibly due to IPA

[gccbugs at rooted dot tk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66271

--- Comment #3 from gccbugs at rooted dot tk ---
Created attachment 35611
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35611&action=edit
gcc -v output

[Bug ipa/66271] -Os generates incorrect code on ARM possibly due to IPA

[gccbugs at rooted dot tk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66271

--- Comment #5 from gccbugs at rooted dot tk ---
Created attachment 35613
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35613&action=edit
C source code

[Bug ipa/66271] -Os generates incorrect code on ARM possibly due to IPA

[gccbugs at rooted dot tk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66271

--- Comment #4 from gccbugs at rooted dot tk ---
Created attachment 35612
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35612&action=edit
incorrect output wiith -Os

[Bug ipa/66271] -Os generates incorrect code on ARM possibly due to IPA

[wilson at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66271

Jim Wilson <wilson at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |wilson at gcc dot gnu.org

--- Comment #6 from Jim Wilson <wilson at gcc dot gnu.org> ---
This appears to be the same problem as 65932.

[Bug ipa/66271] -Os generates incorrect code on ARM possibly due to IPA

[gccbugs at rooted dot tk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66271

--- Comment #7 from gccbugs at rooted dot tk ---
Seems like it is indeed the same issue.

[Bug ipa/66271] -Os generates incorrect code on ARM possibly due to IPA

[wilson at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66271

Jim Wilson <wilson at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|FIXED                       |DUPLICATE

--- Comment #9 from Jim Wilson <wilson at gcc dot gnu.org> ---


*** This bug has been marked as a duplicate of bug 65932 ***