IV29268: INEFFICIENT LOAD OF A 64-BIT CONSTANT

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

• Inefficient constant of sparsely filled 64-bit constants
  
  0x4100000000000001ULL and 0xBEFFFFFFFFFFFFFE
  
  xlC uses inefficient load from constant area of a 64-bit
  constant that has some bits at the beginning and some bits at
  the end (together <= 16-bits). This could be loaded by addi +
  rotate much more efficient.
  
  Sample input:
  $ cat test.C
  extern "C" unsigned long long c41000001()
  {
     return 0x4100000000000001ULL;
  }
  $
  
  extract from listing file:
       | 000000                           PDEF     c41000001
      2|                                  PROC
      4| 000000 ld       E8620008   1     L8
  gr3=.+CONSTANT_AREA
  (gr2,0)
      4| 000004 ld       E8630000   1     L8
  gr3=+CONSTANT_AREA
  (gr3,0)
      5| 000008 bclr     4E800020   1     BA        lr
  

Local fix

• N/A
  

Problem summary

• USERS AFFECTED:
  Any user using 64-bit mode with 64-bit integer constants with
  at least 49 contiguous bits of all 1s or all 0s is affected by
  this issue.
  
  PROBLEM DESCRIPTION:
  A load from the constant area is generated for values which can
  be generated using a load immediate and rotate sequence.
  

Problem conclusion

• The compiler has been improved to exploit load immediate and
  rotate to generate 64-bit integer constants when possible.
  

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:

  LI77326

Fix information

• Fixed component name

  XL C FOR AIX

• Fixed component ID

  5725C7100

Applicable component levels

• RC10 PSY U858497

     UP C