[Bug 1892081] [NEW] Performance improvement when using "QEMU_FLATTEN" with softfloat type conversions

[Ahmed Karaman]

Public bug reported:

Attached below is a matrix multiplication program for double data
types. The program performs the casting operation "(double)rand()"
when generating random numbers.

This operation calls the integer to float softfloat conversion
function "int32_to_float_64".

Adding the "QEMU_FLATTEN" attribute to the function definition
decreases the instructions per call of the function by about 63%.

Attached are before and after performance screenshots from
KCachegrind.

** Affects: qemu
     Importance: Undecided
         Status: New

** Attachment added: "matmult_double.c"
   
https://bugs.launchpad.net/bugs/1892081/+attachment/5402577/+files/matmult_double.c

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https://bugs.launchpad.net/bugs/1892081

Title:
  Performance improvement when using "QEMU_FLATTEN" with softfloat type
  conversions

Status in QEMU:
  New

Bug description:
  Attached below is a matrix multiplication program for double data
  types. The program performs the casting operation "(double)rand()"
  when generating random numbers.

  This operation calls the integer to float softfloat conversion
  function "int32_to_float_64".

  Adding the "QEMU_FLATTEN" attribute to the function definition
  decreases the instructions per call of the function by about 63%.

  Attached are before and after performance screenshots from
  KCachegrind.

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