[Bug rtl-optimization/82111] New: kcoreaddons-5.37.0: desktopfileparser.cpp miscompiled in dbr pass

[danglin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82111

            Bug ID: 82111
           Summary: kcoreaddons-5.37.0: desktopfileparser.cpp miscompiled
                    in dbr pass
           Product: gcc
           Version: 7.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: danglin at gcc dot gnu.org
  Target Milestone: ---
              Host: hppa-unknown-linux-gnu
            Target: hppa-unknown-linux-gnu
             Build: hppa-unknown-linux-gnu

Created attachment 42132
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42132&action=edit
Preprocessed source

The kdelibs4support fails to build on hppa due to a segmentation fault in
desktoptojson.  This is debian bug #874312.

The fault occurs in __sync_sub_and_fetch_4.  It occurs because the r26
argument register is not initialized before the call.

We have in ServiceTypeDefinition::parseValue(QByteArray const&, QString const&)
const the following code:

0x00018cac <+660>:      ldw c(r6),r25
  0x00018cb0 <+664>:    ldw c(ret0),r26
  0x00018cb4 <+668>:    copy r5,r24
  0x00018cb8 <+672>:    add,l r6,r25,r25
  0x00018cbc <+676>:    b,l 0x13144,rp
  0x00018cc0 <+680>:    add,l ret0,r26,r26
  0x00018cc4 <+684>:    cmpib,<> 0,ret0,0x18ac0
<ServiceTypeDefinition::parseValue(QByteArray const&, QString const&)
const+168>
  0x00018cc8 <+688>:    copy r4,r19
  0x00018ccc <+692>:    ldw 4(r3),ret0
  0x00018cd0 <+696>:    ldo -1(ret0),ret0
  0x00018cd4 <+700>:    cmpib,= -1,ret0,0x18cec
<ServiceTypeDefinition::parseValue(QByteArray const&, QString const&)
const+724>
  0x00018cd8 <+704>:    copy r19,r4
  0x00018cdc <+708>:    b,l 0x22a78 <__sync_sub_and_fetch_4>,rp
  0x00018ce0 <+712>:    ldi 1,r25

The call at 0x00018cbc is to memcmp.  When the two cmpib instructions fall
through to the call to __sync_sub_and_fetch_4, the r26 argument register is
not initialized for the call to __sync_sub_and_fetch_4.

The compilation command is:

/usr/lib/gcc/hppa-linux-gnu/7/cc1plus -fpreprocessed desktopfileparser.ii
-quiet -dumpbase desktopfileparser.cpp -auxbase-strip
CMakeFiles/desktoptojson.dir/__/lib/plugin/desktopfileparser.cpp.o -g -O2
-Wformat=1 -Werror=format-security -Wall -Wextra -Wcast-align -Wchar-subscripts
-Wformat-security -Wno-long-long -Wpointer-arith -Wundef -Wnon-virtual-dtor
-Woverloaded-virtual -Werror=return-type -Wvla -Wdate-time -Wpedantic
-Wsuggest-override -std=c++11 -std=gnu++11 -version
-fdebug-prefix-map=/home/dave/debian/kcoreaddons/kcoreaddons-5.37.0=.
-fno-operator-names -fexceptions -fvisibility=hidden
-fvisibility-inlines-hidden -fPIC -o desktopfileparser.s

It appears in looking at the rtl dumps that things go bad in the dbr pass.