IV43942: INEFFICIENT DOUBLE TO 32-BIT UNSIGNED INT CONVERSION

Fixes are available

APAR status

Closed as program error.

Error description

The compiler does not generate efficient code for double to
32-bit unsigned int conversion seen in below  test case.
cat dblToUint32.C
unsigned int toUint32(double in)
{
   return (unsigned int)in;
}
xlC_r -q64 -O2 -qlist -c dblToUint32.C -qarch=pwr5
xlC_r -q64 -O2 -qlist -c dblToUint32.C -qarch=pwr7
Currently, compiler generates:
     | 000000                           PDEF
toUint32(double)
     | 000000                           AKA       toUint32__Fd
    3|                                  PROC      in,vs1
    0| 000000 mfspr    7C0802A6   1     LFLR      gr0=lr
    0| 000004 stdu     F821FF91   1     ST8U
gr1,#stack(gr1,-112)=gr1
    0| 000008 std      F8010080   1     ST8
#stack(gr1,128)=gr0
    5| 00000C bl       4BFFFFF5   1     CALLN
gr3=__uitrunc,1,vs1,gr1,cr[01567]",gr0",gr4"-gr12",vs0"-vs13",mq
",lr",fcr",xer",fsr",ca",ctr",nj",vs0"-vs13",vs32"-vs51"
    5| 000010 ori      60000000   1
    5| 000014 rlwinm   5463003E   1     RN4
gr3=gr3,0,0xFFFFFFFF
    6| 000018 ld       E9810080   1     L8
gr12=#stack(gr1,128)
    6| 00001C addi     38210070   1     AI        gr1=gr1,112
    6| 000020 mtspr    7D8803A6   1     LLR       lr=gr12
    6| 000024 bclr     4E800020   1     BA        lr
    6|                              CL.2:
     |               Tag Table
     | 000028        00000000 00092001 80000000 00000028
     |               Instruction count           10
     |               Straight-line exec time     10
For -qarch=pwr5, fctid[z] instruction is expected.
For -qarch=pwr7, exploitation of xscvdpuxws is expected.

Local fix

```
Modify source code sequence.
```

Problem summary

PROBLEM DESCRIPTION: Using library call __uitrunc instead of
using power 5 and power 7 provided instructions for float to
unsigned word conversion which produces suboptimal performance.

USERS AFFECTED: Anyone that casts a double to an unsigned int.

Problem conclusion

Replaced library calls with code generating instructions for
each of the architectures.

Temporary fix

Comments

APAR Information

APAR number
IV43942
Reported component name
XL C/C++ FOR AI
Reported component ID
5725C7200
Reported release
C10
Status
CLOSED PER
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt
Submitted date
2013-06-10
Closed date
2013-09-18
Last modified date
2013-09-20

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

LI77577 LI77666

Fix information

Fixed component name
XL C FOR AIX
Fixed component ID
5725C7100

Applicable component levels

[{"Line of Business":{"code":"LOB57","label":"Power"},"Business Unit":{"code":"BU058","label":"IBM Infrastructure w\/TPS"},"Product":{"code":"SSGH2K","label":"XL C for AIX"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"12.1"}]

Document Information

Modified date:
02 October 2021

Tips

IV43942: INEFFICIENT DOUBLE TO 32-BIT UNSIGNED INT CONVERSION

Fixes are available

Subscribe

APAR status

Closed as program error.

Error description

Local fix

Problem summary

Problem conclusion

Temporary fix

Comments

APAR Information

APAR number

Reported component name

Reported component ID

Reported release

Status

PE

HIPER

Special Attention

Submitted date

Closed date

Last modified date

APAR is sysrouted FROM one or more of the following:

APAR is sysrouted TO one or more of the following:

Fix information

Fixed component name

Fixed component ID

Applicable component levels

Document Information

Share your feedback

Need support?