491717 - asm_fneg in i386 assembler for SunPro CC is strange; thread safety concern

Status: VERIFIED FIXED

(Tamarin Graveyard :: Baseline JIT (CodegenLIR), defect, P2)

Description

[Lars T Hansen]

The code:

#if defined __SUNPRO_CC
  // from Sun Studio C++ Readme: #pragma align inside namespace requires 
  // mangled names
  static uint32_t temp[] = {0, 0, 0, 0, 0, 0, 0};
  static uint32_t *negateMask = (uint32_t *)alignUp(temp, 16);
  negateMask[1] = 0x80000000;
#else
  static const AVMPLUS_ALIGN16(uint32_t) negateMask[] = {0,0x80000000,0,0};
#endif
  SSE_XORPD(rr, negateMask);

The write to negateMask is probably OK in practice because every thread would write the same value at the same location and every thread would write before it reads; even so, is this code actually necessary?  Selecting one of a short array of constant arrays would seem like the better code.

Comment 1

[Lars T Hansen]

Blocks a P2/Flash10.x bug.

Comment 2

[Lars T Hansen]

Attachment: Patch

Move the initialization to the global level, where (presumably) standard initialization of statics will ensure that it's initialized before a second thread is created.

Comment 3

[Lars T Hansen]

redux changeset:   2605:07a7e0e8361f