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__SMLALD() produces suboptimal code

Ilija Kocho
Note: This was originally posted on 19th August 2013 at http://forums.arm.com

__SMLALD() as implemented in core_cm4_simd.h (V3.20) produces suboptimal code (at leas with GCC).

Example:
sample = *samp2_p++; \
re = __SMLALD(ortho_p[COS2_O], sample, re); \
im = __SMLALD(ortho_p[SIN2_O], sample, im); \
ortho_p++;

Produced code [GCC 4.8.1 with -O2 optimization]:
  a94: 4682       mov sl, r0
  a96: f10c 0304  add.w r3, ip, #4
  a9a: f8d4 0100  ldr.w r0, [r4, #256] ; 0x100
  a9e: f8dc c000  ldr.w ip, [ip]
  aa2: fbc0 a8cc  smlald sl, r8, r0, ip
  aa6: 2000       movs r0, #0
  aa8: 9022       str r0, [sp, #136] ; 0x88
  aaa: f8cd 808c  str.w r8, [sp, #140] ; 0x8c
  aae: e9dd 8922  ldrd r8, r9, [sp, #136] ; 0x88
  ab2: f854 0b04  ldr.w r0, [r4], #4
  ab6: ea48 080a  orr.w r8, r8, sl
  aba: fbc0 21cc  smlald r2, r1, r0, ip
  abe: 9125       str r1, [sp, #148] ; 0x94
  ac0: 2100       movs r1, #0
  ac2: 9124       str r1, [sp, #144] ; 0x90
  ac4: e9dd 0124  ldrd r0, r1, [sp, #144] ; 0x90
  ac8: ea40 0002  orr.w r0, r0, r2
  acc: 468a       mov sl, r1
  ace: 4684       mov ip, r0
  ad0: 464a       mov r2, r9

I propose following implementation:

typedef union llreg_u{
  uint32_t w32[2];
  uint64_t w64;
} llreg_t;

__attribute__( ( always_inline ) ) __STATIC_INLINE uint64_t __SMLALD (uint32_t op1, uint32_t op2, uint64_t result)
{
  llreg_t llr;
  llr.w64 = result;

  __ASM volatile ("smlald %0, %1, %2, %3" : "=r" (llr.w32[0]), "=r" (llr.w32[1]): "r" (op1), "r" (op2) , "0" (llr.w32[0]), "1" (llr.w32[1]) );

  return(llr.w64);
}

that produces following code [GCC 4.8.1 with -O2 optimization]:
  a96: f109 0504  add.w r5, r9, #4
  a9a: f8d9 c000  ldr.w ip, [r9]
  a9e: f8d3 2100  ldr.w r2, [r3, #256] ; 0x100
  aa2: fbc2 40cc  smlald r4, r0, r2, ip
  aa6: 9a01    ldr r2, [sp, #4]
  aa8: f853 9b04  ldr.w r9, [r3], #4
  aac: fbc9 12cc  smlald r1, r2, r9, ip

Notes:
1. The proposed code assumes little endian but preparation for big endian is trivial.
2. Similar optimization can be applied to __SMLALD() siblings.

Ilija
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