s_bcnt1_i32_b64 GPU Native ISA AMD Scalar

Scalar Arithmetic

s_bcnt1_i32_b64

Count the number of "1" bits in a scalar input, store the result into a scalar register and set SCC iff the result is nonzero.

Encoding

Binary Layout (AMD CDNA 5)
101111101
31:23
SDST
22:16
00011001
15:8
SSRC0
7:0
 

The ENC_SOP1 layout from AMD's machine-readable ISA specification (AMD CDNA 5). Opcode 25 in OP rebuilds 0xBE801900, an identifier AMD lists for this encoding. Not the same in every generation: AMD CDNA 4 (opcode 13), AMD CDNA 3 (opcode 13), AMD CDNA 2 (opcode 13), AMD CDNA 1 (opcode 13), AMD RDNA 2 (opcode 16), AMD RDNA 1 (opcode 16). The same in AMD RDNA 4, AMD RDNA 3.5, AMD RDNA 3.

Format SOP1
Width 32 bits
Opcode 25
Identifier 0xBE801900

Operands

  • SDST
    Written. All scalar destination operands. Data format: Signed 32-bit integral data. (OPR_SDST, FMT_NUM_I32)
  • SSRC0
    Read. All scalar operands. Covers all operands that are allowed as scalar sources. Data format: Unsigned 64-bit integral data. (OPR_SSRC, FMT_NUM_U64)

In AMD's order, as its machine-readable ISA specification lists them for the ENC_SOP1 encoding (AMD CDNA 5).

GFX Target Compatibility

TargetSupport
gfx1100✅ Supported

Related

More in Scalar Arithmetic

Reference

AMDGPU / GFX ISA

Semantics

tmp = 0; for i in 0 : 63 do tmp += S0.u64[i] == 1'1U ? 1 : 0 endfor; D0.i32 = tmp; SCC = D0.u64 != 0ULL

Example

s_bcnt1_i32_b64 s0, 0

A real instruction accepted by the LLVM assembler, taken verbatim from LLVM's own AMDGPU MC test suite. Not from an AMD document, and not authored here.

Sources