IV28620: INEFFICIENT STRUCT/UNION INIT OF MEMBER

March 2013 PTF for XL C for AIX, V12.1
March 2013 PTF for XL C/C++ for AIX, V12.1

APAR status

• Closed as program error.

Error description

• xlC initializes struct and union member with inefficient loads
  from constant area while load immediate could be used to
  create the values that are stored to the struct/union.
  
  
  ===== COMPILE COMMAND:
  xlC -q64 -O2 -qlist -c test.C
  
  
  ===== TESTCASE:
  $ cat test.C
  struct  sqlz_value
  {
     unsigned short type;
     union
     {
        unsigned short clen;
        struct
        {
           unsigned char m;
           unsigned char n;
        } dlen;
     } len;
     unsigned char *data;
  };
  
  extern "C" void intToDec(struct sqlz_value *dec, int i);
  
  extern "C" void init(int i)
  {
     struct sqlz_value promote;
     promote.type = 2;
     promote.len.dlen.m = 11;
     promote.len.dlen.n = 0;
     intToDec(&promote, i);
  }
  $
  
  
  When looking at the provided test case, only the 0 gets loaded
  using li.
  But for 11, two loads from constant area are used.
  
   18|                                  PROC      i,gr3
      0| 000000 mfspr    7C0802A6   1     LFLR      gr0=lr
      0| 000004 ld       E8A20008   1     L8
  gr5=.+CONSTANT_AREA(gr2,0)
      0| 000008 stdu     F821FF81   1     ST8U
  gr1,#stack(gr1,-128)=gr1
     24| 00000C extsw    7C6407B4   1     EXTS4     gr4=gr3
     24| 000010 addi     38610070   1     AI        gr3=gr1,112
      0| 000014 std      F8010090   1     ST8
  #stack(gr1,144)=gr0
     23| 000018 addi     38000000   1     LI        gr0=0
     23| 00001C stb      98010073   1     ST1Z
  <a1:d115:l1>(gr1,115)=gr0
     22| 000020 lhz      A0050000   1     L2Z
  gr0=+CONSTANT_AREA(gr5,0) <---- here
     22| 000024 lbz      88A50002   1     L1Z
  gr5=+CONSTANT_AREA(gr5,2) <---- here
     22| 000028 sth      B0010070   1     ST2Z
  promote.|type@0#11|m@2#12_1(gr1,112)=gr0
     22| 00002C stb      98A10072   1     ST1Z
  promote.|type@0#11|m@2#12_1(gr1,114)=gr5
     24| 000030 bl       4BFFFFD1   1     CALL
  intToDec,2,promote",gr3,gr4,#ProcAlias",intToDec",fcr",gr1,cr[01
  567]",gr0",gr3"-gr12",fp0"-fp13",mq",lr",fcr",xer",fsr",ca",ctr"
     24| 000034 ori      60000000   1
     25| 000038 ld       E9810090   1     L8
  gr12=#stack(gr1,144)
     25| 00003C addi     38210080   1     AI        gr1=gr1,128
     25| 000040 mtspr    7D8803A6   1     LLR       lr=gr12
     25| 000044 bclr     4E800020   1     BA        lr
  

Local fix

• n/a
  

Problem summary

• TBD
  

Problem conclusion

• TBD
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  LI77123

Fix information

• Fixed component name

  XL C FOR AIX

• Fixed component ID

  5725C7100

Applicable component levels

• RC10 PSY U856101

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