OV - attention-clang-gnr256 - Loop 79 - attention-clang-gnr256

	Loop Id: 79	Module: attention-clang-gnr256	Source: attention_v2.cpp:27-33	Coverage: 0.66%

0x4be0 VCVTSD2SS	%XMM0,%XMM0,%XMM0

0x4be4 MOV	0x60(%RSP),%RAX

0x4be9 LEA	(%RAX,%R8,1),%R9D

0x4bed MOV	0xd8(%RSP),%RAX

0x4bf5 VMOVSS	%XMM0,(%RAX,%R9,4)

0x4bfb INC	%R8

0x4bfe MOV	0x28(%RSP),%R9

0x4c03 CMP	%R9,%R8

0x4c06 JE	4b8c

0x4c08 CMP	$0x3,%R9D

0x4c0c JBE	4c28

0x4c0e MOV	%R8D,%R9D

0x4c11 ADD	0x98(%RSP),%R9D

0x4c19 SETB	%R9B

0x4c1d OR	0x20(%RSP),%R9B

0x4c22 JE	6b47

0x4c28 CMPQ	$0x3,0x98(%RSP)

0x4c31 JAE	4c40

0x4c33 VXORPS	%XMM0,%XMM0,%XMM0

0x4c37 XOR	%R9D,%R9D

0x4c3a JMP	4d0a

0x4c40 VXORPS	%XMM0,%XMM0,%XMM0

0x4c44 MOV	%R8,%R10

0x4c47 XOR	%R9D,%R9D

0x4c4a MOV	0x218(%RSP),%RDX

0x4c52 MOV	0x290(%RSP),%RAX

0x4c5a MOV	0x220(%RSP),%RDI

0x4c62 MOV	0x288(%RSP),%RSI

0x4c6a NOPW	(%RAX,%RAX,1)

  (42) 0x4c70 LEA	(%RCX,%R9,1),%R11D

  (42) 0x4c74 VMOVSS	(%R14,%R11,4),%XMM1

  (42) 0x4c7a VCVTSS2SD	%XMM1,%XMM1,%XMM1

  (42) 0x4c7e MOV	%R10D,%R11D

  (42) 0x4c81 VMOVSS	(%R13,%R11,4),%XMM2

  (42) 0x4c88 VCVTSS2SD	%XMM2,%XMM2,%XMM2

  (42) 0x4c8c VFMADD213SD	%XMM0,%XMM1,%XMM2

  (42) 0x4c91 LEA	0x1(%RCX,%R9,1),%R11D

  (42) 0x4c96 VMOVSS	(%R14,%R11,4),%XMM0

  (42) 0x4c9c VCVTSS2SD	%XMM0,%XMM0,%XMM0

  (42) 0x4ca0 LEA	(%RBX,%R10,1),%R11D

  (42) 0x4ca4 VMOVSS	(%R13,%R11,4),%XMM1

  (42) 0x4cab VCVTSS2SD	%XMM1,%XMM1,%XMM1

  (42) 0x4caf LEA	0x2(%RCX,%R9,1),%R11D

  (42) 0x4cb4 VMOVSS	(%R14,%R11,4),%XMM3

  (42) 0x4cba VCVTSS2SD	%XMM3,%XMM3,%XMM3

  (42) 0x4cbe VFMADD213SD	%XMM2,%XMM0,%XMM1

  (42) 0x4cc3 LEA	(%RSI,%R10,1),%R11D

  (42) 0x4cc7 VMOVSS	(%R13,%R11,4),%XMM0

  (42) 0x4cce VCVTSS2SD	%XMM0,%XMM0,%XMM2

  (42) 0x4cd2 VFMADD213SD	%XMM1,%XMM3,%XMM2

  (42) 0x4cd7 LEA	0x3(%RCX,%R9,1),%R11D

  (42) 0x4cdc VMOVSS	(%R14,%R11,4),%XMM0

  (42) 0x4ce2 VCVTSS2SD	%XMM0,%XMM0,%XMM1

  (42) 0x4ce6 LEA	(%RAX,%R10,1),%R11D

  (42) 0x4cea VMOVSS	(%R13,%R11,4),%XMM0

  (42) 0x4cf1 VCVTSS2SD	%XMM0,%XMM0,%XMM0

  (42) 0x4cf5 VFMADD213SD	%XMM2,%XMM1,%XMM0

  (42) 0x4cfa ADD	$0x4,%R9

  (42) 0x4cfe ADD	%RDI,%R10

  (42) 0x4d01 CMP	%R9,%RDX

  (42) 0x4d04 JNE	4c70

0x4d0a TEST	$0x3,%BL

0x4d0d JE	4be0

0x4d13 MOV	%RBX,%R10

0x4d16 IMUL	%R9,%R10

0x4d1a ADD	%R8,%R10

0x4d1d ADD	%ECX,%R9D

0x4d20 MOV	0x1a0(%RSP),%R11

0x4d28 NOPL	(%RAX,%RAX,1)

  (80) 0x4d30 MOV	%R9D,%EBX

  (80) 0x4d33 VMOVSS	(%R14,%RBX,4),%XMM1

  (80) 0x4d39 VCVTSS2SD	%XMM1,%XMM1,%XMM1

  (80) 0x4d3d MOV	%R10D,%EBX

  (80) 0x4d40 VMOVSS	(%R13,%RBX,4),%XMM2

  (80) 0x4d47 MOV	0x38(%RSP),%RBX

  (80) 0x4d4c VCVTSS2SD	%XMM2,%XMM2,%XMM2

  (80) 0x4d50 VFMADD231SD	%XMM2,%XMM1,%XMM0

  (80) 0x4d55 ADD	%RBX,%R10

  (80) 0x4d58 INC	%R9D

  (80) 0x4d5b DEC	%R11

  (80) 0x4d5e JNE	4d30

0x4d60 JMP	4be0

/home/eoseret/llm-attention/attention_v2.cpp: 27 - 33

--------------------------------------------------------------------------------

27:       for (unsigned int j = 0; j < N; ++j) {  //vectorized

28:          double sum = 0.0;

29: #pragma clang loop vectorize(enable)

30:          for (unsigned int k = 0; k < K; ++k) { //vectorized

31:             sum += (double)A[i * K + k] * (double)B[k * N + j];

32:          }

33:          C[i * N + j] = alpha * static_cast<float>(sum);

Coverage (%)	Name	Source Location	Module

min	med	avg	max

Percentile Index	10	20	30	40	50	60	70	80	90	100
Value

min	med	avg	max

Percentile Index	10	20	30	40	50	60	70	80	90	100
Value

Path /

Metric	Value
CQA speedup if no scalar integer	2.17
CQA speedup if FP arith vectorized	1.00
CQA speedup if fully vectorized	12.94
CQA speedup if no inter-iteration dependency	NA
CQA speedup if next bottleneck killed	1.76
Bottlenecks	micro-operation queue,
Function	main
Source	attention_v2.cpp:27-27,attention_v2.cpp:30-30,attention_v2.cpp:33-33
Source loop unroll info	NA
Source loop unroll confidence level	NA
Unroll/vectorization loop type	NA
Unroll factor	NA
CQA cycles	6.50
CQA cycles if no scalar integer	3.00
CQA cycles if FP arith vectorized	6.50
CQA cycles if fully vectorized	0.50
Front-end cycles	6.50
P0 cycles	3.70
P1 cycles	3.60
P2 cycles	3.67
P3 cycles	3.67
P4 cycles	0.50
P5 cycles	3.60
P6 cycles	3.50
P7 cycles	0.50
P8 cycles	0.50
P9 cycles	0.50
P10 cycles	3.60
P11 cycles	3.67
DIV/SQRT cycles	0.00
Inter-iter dependencies cycles	NA
FE+BE cycles (UFS)	NA
Stall cycles (UFS)	NA
Nb insns	38.00
Nb uops	39.00
Nb loads	11.00
Nb stores	1.00
Nb stack references	10.00
FLOP/cycle	0.00
Nb FLOP add-sub	0.00
Nb FLOP mul	0.00
Nb FLOP fma	0.00
Nb FLOP div	0.00
Nb FLOP rcp	0.00
Nb FLOP sqrt	0.00
Nb FLOP rsqrt	0.00
Bytes/cycle	12.46
Bytes prefetched	0.00
Bytes loaded	77.00
Bytes stored	4.00
Stride 0	NA
Stride 1	NA
Stride n	NA
Stride unknown	NA
Stride indirect	NA
Vectorization ratio all	13.33
Vectorization ratio load	0.00
Vectorization ratio store	0.00
Vectorization ratio mul	0.00
Vectorization ratio add_sub	0.00
Vectorization ratio fma	NA
Vectorization ratio div_sqrt	NA
Vectorization ratio other	25.00
Vector-efficiency ratio all	13.33
Vector-efficiency ratio load	12.50
Vector-efficiency ratio store	6.25
Vector-efficiency ratio mul	12.50
Vector-efficiency ratio add_sub	12.50
Vector-efficiency ratio fma	NA
Vector-efficiency ratio div_sqrt	NA
Vector-efficiency ratio other	14.84

Metric	Value
CQA speedup if no scalar integer	2.17
CQA speedup if FP arith vectorized	1.00
CQA speedup if fully vectorized	12.94
CQA speedup if no inter-iteration dependency	NA
CQA speedup if next bottleneck killed	1.76
Bottlenecks	micro-operation queue,
Function	main
Source	attention_v2.cpp:27-27,attention_v2.cpp:30-30,attention_v2.cpp:33-33
Source loop unroll info	NA
Source loop unroll confidence level	NA
Unroll/vectorization loop type	NA
Unroll factor	NA
CQA cycles	6.50
CQA cycles if no scalar integer	3.00
CQA cycles if FP arith vectorized	6.50
CQA cycles if fully vectorized	0.50
Front-end cycles	6.50
P0 cycles	3.70
P1 cycles	3.60
P2 cycles	3.67
P3 cycles	3.67
P4 cycles	0.50
P5 cycles	3.60
P6 cycles	3.50
P7 cycles	0.50
P8 cycles	0.50
P9 cycles	0.50
P10 cycles	3.60
P11 cycles	3.67
DIV/SQRT cycles	0.00
Inter-iter dependencies cycles	NA
FE+BE cycles (UFS)	NA
Stall cycles (UFS)	NA
Nb insns	38.00
Nb uops	39.00
Nb loads	11.00
Nb stores	1.00
Nb stack references	10.00
FLOP/cycle	0.00
Nb FLOP add-sub	0.00
Nb FLOP mul	0.00
Nb FLOP fma	0.00
Nb FLOP div	0.00
Nb FLOP rcp	0.00
Nb FLOP sqrt	0.00
Nb FLOP rsqrt	0.00
Bytes/cycle	12.46
Bytes prefetched	0.00
Bytes loaded	77.00
Bytes stored	4.00
Stride 0	NA
Stride 1	NA
Stride n	NA
Stride unknown	NA
Stride indirect	NA
Vectorization ratio all	13.33
Vectorization ratio load	0.00
Vectorization ratio store	0.00
Vectorization ratio mul	0.00
Vectorization ratio add_sub	0.00
Vectorization ratio fma	NA
Vectorization ratio div_sqrt	NA
Vectorization ratio other	25.00
Vector-efficiency ratio all	13.33
Vector-efficiency ratio load	12.50
Vector-efficiency ratio store	6.25
Vector-efficiency ratio mul	12.50
Vector-efficiency ratio add_sub	12.50
Vector-efficiency ratio fma	NA
Vector-efficiency ratio div_sqrt	NA
Vector-efficiency ratio other	14.84

Path /

Average path: Display a virtual path defined by average values of all real paths

Function	main
Source file and lines	attention_v2.cpp:27-33
Module	attention-clang-gnr256

The loop is defined in /home/eoseret/llm-attention/attention_v2.cpp:27-33.

Analyzed code is defined in /home/eoseret/llm-attention/attention_v2.cpp:27,30,33.

Warnings:

Non-innermost loop: analyzing only self part (ignoring child loops).
Ignoring paths for analysis
Too many paths. Rerun with max-paths=8
RecMII not computed since number of paths is unknown or > max_paths
Streams not analyzed since number of paths is unknown or > max_paths

Try to simplify control and/or increase the maximum number of paths per function/loop through the 'max-paths-nb' option.

This loop has 8 execution paths.

The presence of multiple execution paths is typically the main/first bottleneck.
Try to simplify control inside loop: ideally, try to remove all conditional expressions, for example by (if applicable):

hoisting them (moving them outside the loop)
turning them into conditional moves, MIN or MAX

Ex: if (x<0) x=0 => x = (x<0 ? 0 : x) (or MAX(0,x) after defining the corresponding macro)

gain
potential
hint
expert

Code clean check

Detected a slowdown caused by scalar integer instructions (typically used for address computation). By removing them, you can lower the cost of an iteration from 6.50 to 3.00 cycles (2.17x speedup).

Workaround

Try to reorganize arrays of structures to structures of arrays
Consider to permute loops (see vectorization gain report)

Vectorization

Your loop is probably not vectorized. Only 13% of vector register length is used (average across all SSE/AVX instructions). By vectorizing your loop, you can lower the cost of an iteration from 6.50 to 0.50 cycles (12.94x speedup).

Details

Store and arithmetical SSE/AVX instructions are used in scalar version (process only one data element in vector registers). Since your execution units are vector units, only a vectorized loop can use their full power.

Workaround

Try another compiler or update/tune your current one:
- recompile with ffast-math (included in Ofast) to extend loop vectorization to FP reductions.
Remove inter-iterations dependences from your loop and make it unit-stride:
- If your arrays have 2 or more dimensions, check whether elements are accessed contiguously and, otherwise, try to permute loops accordingly: C storage order is row-major: for(i) for(j) a[j][i] = b[j][i]; (slow, non stride 1) => for(i) for(j) a[i][j] = b[i][j]; (fast, stride 1)
- If your loop streams arrays of structures (AoS), try to use structures of arrays instead (SoA): for(i) a[i].x = b[i].x; (slow, non stride 1) => for(i) a.x[i] = b.x[i]; (fast, stride 1)

Execution units bottlenecks

Found no such bottlenecks but see expert reports for more complex bottlenecks.

No data for this section

Complex instructions

Detected COMPLEX INSTRUCTIONS.

Details

These instructions generate more than one micro-operation and only one of them can be decoded during a cycle and the extra micro-operations increase pressure on execution units.

VCVTSD2SS: 1 occurrences►
- /home/eoseret/llm-attention/attention_v2.cpp:33

Conversion instructions

Detected expensive conversion instructions.

Details

VCVTSD2SS (FP64 to FP32, scalar): 1 occurrences►
- /home/eoseret/llm-attention/attention_v2.cpp:33

Workaround

Avoid mixing data with different types. In particular, check if the type of constants is the same as array elements. Use double instead of single precision only when/where needed by numerical stability and avoid mixing precision. In C/C++, FP constants are double precision by default and must be suffixed by 'f' to make them single precision.

Type of elements and instruction set

No instructions are processing arithmetic or math operations on FP elements. This loop is probably writing/copying data or processing integer elements.

Matching between your loop (in the source code) and the binary loop

The binary loop does not contain any FP arithmetical operations. The binary loop is loading 77 bytes. The binary loop is storing 4 bytes.

General properties

nb instructions	38
nb uops	39
loop length	186
used x86 registers	11
used mmx registers	0
used xmm registers	1
used ymm registers	0
used zmm registers	0
nb stack references	10

Front-end

MACRO FUSION NOT POSSIBLE FIT IN UOP CACHE

micro-operation queue	6.50 cycles
front end	6.50 cycles

Back-end

	P0	P1	P2	P3	P4	P5	P6	P7	P8	P9	P10	P11
uops	3.70	3.60	3.67	3.67	0.50	3.60	3.50	0.50	0.50	0.50	3.60	3.67
cycles	3.70	3.60	3.67	3.67	0.50	3.60	3.50	0.50	0.50	0.50	3.60	3.67

Execution ports to units layout:

P0 (256 bits): VPU, BRU, ALU, DIV/SQRT
P1 (256 bits): ALU, VPU
P2 (512 bits): load
P3 (512 bits): load
P4 (512 bits): store data
P5 (512 bits): ALU, VPU
P6: ALU, BRU
P7: store address
P8: store address
P9 (512 bits): store data
P10: ALU
P11 (512 bits): load

Cycles executing div or sqrt instructions

Cycles summary

Front-end	6.50
Dispatch	3.70
Overall L1	6.50

Vectorization ratios

INT

all	0%
load	0%
store	NA (no store vectorizable/vectorized instructions)
mul	0%
add-sub	0%
fma	NA (no fma vectorizable/vectorized instructions)
other	0%

all	50%
load	NA (no load vectorizable/vectorized instructions)
store	0%
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	NA (no add-sub vectorizable/vectorized instructions)
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	NA (no div/sqrt vectorizable/vectorized instructions)
other	66%

INT+FP

all	13%
load	0%
store	0%
mul	0%
add-sub	0%
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	NA (no div/sqrt vectorizable/vectorized instructions)
other	25%

Vector efficiency ratios

INT

all	11%
load	12%
store	NA (no store vectorizable/vectorized instructions)
mul	12%
add-sub	12%
fma	NA (no fma vectorizable/vectorized instructions)
other	11%

all	17%
load	NA (no load vectorizable/vectorized instructions)
store	6%
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	NA (no add-sub vectorizable/vectorized instructions)
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	NA (no div/sqrt vectorizable/vectorized instructions)
other	20%

INT+FP

all	13%
load	12%
store	6%
mul	12%
add-sub	12%
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	NA (no div/sqrt vectorizable/vectorized instructions)
other	14%

Cycles and memory resources usage

Assuming all data fit into the L1 cache, each iteration of the binary loop takes 6.50 cycles. At this rate:

6% of peak load performance is reached (11.85 out of 192.00 bytes loaded per cycle (GB/s @ 1GHz))
0% of peak store performance is reached (0.62 out of 128.00 bytes stored per cycle (GB/s @ 1GHz))

Front-end bottlenecks

Performance is limited by instruction throughput (loading/decoding program instructions to execution core) (front-end is a bottleneck). By removing all these bottlenecks, you can lower the cost of an iteration from 6.50 to 3.70 cycles (1.76x speedup).

ASM code

In the binary file, the address of the loop is: 4c08

Instruction	Nb FU	P0	P1	P2	P3	P4	P5	P6	P7	P8	P9	P10	P11	Latency	Recip. throughput	Vectorization
VCVTSD2SS %XMM0,%XMM0,%XMM0	2	0.50	0.50	0	0	0	1	0	0	0	0	0	0	5	1	scal (12.5%)
MOV 0x60(%RSP),%RAX	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	N/A
LEA (%RAX,%R8,1),%R9D	1	0.20	0.20	0	0	0	0.20	0.20	0	0	0	0.20	0	1-2	0.20	N/A
MOV 0xd8(%RSP),%RAX	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	N/A
VMOVSS %XMM0,(%RAX,%R9,4)	1	0	0	0	0	0.50	0	0	0.50	0.50	0.50	0	0	1	0.50	scal (6.3%)
INC %R8	1	0	0	0	0	0	0	0	0	0	0	0	0	1	0.17	N/A
MOV 0x28(%RSP),%R9	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	N/A
CMP %R9,%R8	1	0.20	0.20	0	0	0	0.20	0.20	0	0	0	0.20	0	1	0.20	scal (12.5%)
JE 4b8c <main+0x1e7c>	1	0.50	0	0	0	0	0	0.50	0	0	0	0	0	0	0.50	N/A
CMP $0x3,%R9D	1	0.20	0.20	0	0	0	0.20	0.20	0	0	0	0.20	0	1	0.20	scal (6.3%)
JBE 4c28 <main+0x1f18>	1	0.50	0	0	0	0	0	0.50	0	0	0	0	0	0	0.50	N/A
MOV %R8D,%R9D	1	0	0	0	0	0	0	0	0	0	0	0	0	1	0.17	N/A
ADD 0x98(%RSP),%R9D	1	0.20	0.20	0.33	0.33	0	0.20	0.20	0	0	0	0.20	0.33	1	0.33	N/A
SETB %R9B	1	0.50	0	0	0	0	0	0.50	0	0	0	0	0	1	0.50	N/A
OR 0x20(%RSP),%R9B	1	0.20	0.20	0.33	0.33	0	0.20	0.20	0	0	0	0.20	0.33	1-2	0.33	N/A
JE 6b47 <main+0x3e37>	1	0.50	0	0	0	0	0	0.50	0	0	0	0	0	0	0.50	N/A
CMPQ $0x3,0x98(%RSP)	1	0.20	0.20	0.33	0.33	0	0.20	0.20	0	0	0	0.20	0.33	1	0.33	scal (12.5%)
JAE 4c40 <main+0x1f30>	1	0.50	0	0	0	0	0	0.50	0	0	0	0	0	0	0.50	N/A
VXORPS %XMM0,%XMM0,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0.17	vect (25.0%)
XOR %R9D,%R9D	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0.17	N/A
JMP 4d0a <main+0x1ffa>	1	0	0	0	0	0	0	0	0	0	0	0	0	0	2.08	N/A
VXORPS %XMM0,%XMM0,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0.17	vect (25.0%)
MOV %R8,%R10	1	0	0	0	0	0	0	0	0	0	0	0	0	1	0.17	scal (12.5%)
XOR %R9D,%R9D	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0.17	N/A
MOV 0x218(%RSP),%RDX	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	scal (12.5%)
MOV 0x290(%RSP),%RAX	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	N/A
MOV 0x220(%RSP),%RDI	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	scal (12.5%)
MOV 0x288(%RSP),%RSI	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	scal (12.5%)
NOPW (%RAX,%RAX,1)	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0.17	N/A
TEST $0x3,%BL	1	0.20	0.20	0	0	0	0.20	0.20	0	0	0	0.20	0	2	0.20	N/A
JE 4be0 <main+0x1ed0>	1	0.50	0	0	0	0	0	0.50	0	0	0	0	0	0	0.50	N/A
MOV %RBX,%R10	1	0	0	0	0	0	0	0	0	0	0	0	0	1	0.17	scal (12.5%)
IMUL %R9,%R10	1	0	1	0	0	0	0	0	0	0	0	0	0	3	1	scal (12.5%)
ADD %R8,%R10	1	0.20	0.20	0	0	0	0.20	0.20	0	0	0	0.20	0	1	0.20	scal (12.5%)
ADD %ECX,%R9D	1	0.20	0.20	0	0	0	0.20	0.20	0	0	0	0.20	0	1	0.20	N/A
MOV 0x1a0(%RSP),%R11	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	scal (12.5%)
NOPL (%RAX,%RAX,1)	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0.17	N/A
JMP 4be0 <main+0x1ed0>	1	0	0	0	0	0	0	0	0	0	0	0	0	0	2.08	N/A

Function	main
Source file and lines	attention_v2.cpp:27-33
Module	attention-clang-gnr256

The loop is defined in /home/eoseret/llm-attention/attention_v2.cpp:27-33.

Analyzed code is defined in /home/eoseret/llm-attention/attention_v2.cpp:27,30,33.

Warnings:

Non-innermost loop: analyzing only self part (ignoring child loops).
Ignoring paths for analysis
Too many paths. Rerun with max-paths=8
RecMII not computed since number of paths is unknown or > max_paths
Streams not analyzed since number of paths is unknown or > max_paths

hoisting them (moving them outside the loop)
turning them into conditional moves, MIN or MAX

Ex: if (x<0) x=0 => x = (x<0 ? 0 : x) (or MAX(0,x) after defining the corresponding macro)

gain
potential
hint
expert

Code clean check

Detected a slowdown caused by scalar integer instructions (typically used for address computation). By removing them, you can lower the cost of an iteration from 6.50 to 3.00 cycles (2.17x speedup).

Workaround

Try to reorganize arrays of structures to structures of arrays
Consider to permute loops (see vectorization gain report)

Vectorization

Details

Workaround

Try another compiler or update/tune your current one:
- recompile with ffast-math (included in Ofast) to extend loop vectorization to FP reductions.
Remove inter-iterations dependences from your loop and make it unit-stride:
- If your arrays have 2 or more dimensions, check whether elements are accessed contiguously and, otherwise, try to permute loops accordingly: C storage order is row-major: for(i) for(j) a[j][i] = b[j][i]; (slow, non stride 1) => for(i) for(j) a[i][j] = b[i][j]; (fast, stride 1)
- If your loop streams arrays of structures (AoS), try to use structures of arrays instead (SoA): for(i) a[i].x = b[i].x; (slow, non stride 1) => for(i) a.x[i] = b.x[i]; (fast, stride 1)

Execution units bottlenecks

Found no such bottlenecks but see expert reports for more complex bottlenecks.

No data for this section

Complex instructions

Detected COMPLEX INSTRUCTIONS.

Details

These instructions generate more than one micro-operation and only one of them can be decoded during a cycle and the extra micro-operations increase pressure on execution units.

VCVTSD2SS: 1 occurrences►
- /home/eoseret/llm-attention/attention_v2.cpp:33

Conversion instructions

Detected expensive conversion instructions.

Details

VCVTSD2SS (FP64 to FP32, scalar): 1 occurrences►
- /home/eoseret/llm-attention/attention_v2.cpp:33

Workaround

Type of elements and instruction set

No instructions are processing arithmetic or math operations on FP elements. This loop is probably writing/copying data or processing integer elements.

Matching between your loop (in the source code) and the binary loop

The binary loop does not contain any FP arithmetical operations. The binary loop is loading 77 bytes. The binary loop is storing 4 bytes.

General properties

nb instructions	38
nb uops	39
loop length	186
used x86 registers	11
used mmx registers	0
used xmm registers	1
used ymm registers	0
used zmm registers	0
nb stack references	10

Front-end

MACRO FUSION NOT POSSIBLE FIT IN UOP CACHE

micro-operation queue	6.50 cycles
front end	6.50 cycles

Back-end

	P0	P1	P2	P3	P4	P5	P6	P7	P8	P9	P10	P11
uops	3.70	3.60	3.67	3.67	0.50	3.60	3.50	0.50	0.50	0.50	3.60	3.67
cycles	3.70	3.60	3.67	3.67	0.50	3.60	3.50	0.50	0.50	0.50	3.60	3.67

Execution ports to units layout:

P0 (256 bits): VPU, BRU, ALU, DIV/SQRT
P1 (256 bits): ALU, VPU
P2 (512 bits): load
P3 (512 bits): load
P4 (512 bits): store data
P5 (512 bits): ALU, VPU
P6: ALU, BRU
P7: store address
P8: store address
P9 (512 bits): store data
P10: ALU
P11 (512 bits): load

Cycles executing div or sqrt instructions

Cycles summary

Front-end	6.50
Dispatch	3.70
Overall L1	6.50

Vectorization ratios

INT

all	0%
load	0%
store	NA (no store vectorizable/vectorized instructions)
mul	0%
add-sub	0%
fma	NA (no fma vectorizable/vectorized instructions)
other	0%

all	50%
load	NA (no load vectorizable/vectorized instructions)
store	0%
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	NA (no add-sub vectorizable/vectorized instructions)
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	NA (no div/sqrt vectorizable/vectorized instructions)
other	66%

INT+FP

all	13%
load	0%
store	0%
mul	0%
add-sub	0%
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	NA (no div/sqrt vectorizable/vectorized instructions)
other	25%

Vector efficiency ratios

INT

all	11%
load	12%
store	NA (no store vectorizable/vectorized instructions)
mul	12%
add-sub	12%
fma	NA (no fma vectorizable/vectorized instructions)
other	11%

all	17%
load	NA (no load vectorizable/vectorized instructions)
store	6%
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	NA (no add-sub vectorizable/vectorized instructions)
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	NA (no div/sqrt vectorizable/vectorized instructions)
other	20%

INT+FP

all	13%
load	12%
store	6%
mul	12%
add-sub	12%
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	NA (no div/sqrt vectorizable/vectorized instructions)
other	14%

Cycles and memory resources usage

Assuming all data fit into the L1 cache, each iteration of the binary loop takes 6.50 cycles. At this rate:

6% of peak load performance is reached (11.85 out of 192.00 bytes loaded per cycle (GB/s @ 1GHz))
0% of peak store performance is reached (0.62 out of 128.00 bytes stored per cycle (GB/s @ 1GHz))

Front-end bottlenecks

ASM code

In the binary file, the address of the loop is: 4c08

Instruction	Nb FU	P0	P1	P2	P3	P4	P5	P6	P7	P8	P9	P10	P11	Latency	Recip. throughput	Vectorization
VCVTSD2SS %XMM0,%XMM0,%XMM0	2	0.50	0.50	0	0	0	1	0	0	0	0	0	0	5	1	scal (12.5%)
MOV 0x60(%RSP),%RAX	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	N/A
LEA (%RAX,%R8,1),%R9D	1	0.20	0.20	0	0	0	0.20	0.20	0	0	0	0.20	0	1-2	0.20	N/A
MOV 0xd8(%RSP),%RAX	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	N/A
VMOVSS %XMM0,(%RAX,%R9,4)	1	0	0	0	0	0.50	0	0	0.50	0.50	0.50	0	0	1	0.50	scal (6.3%)
INC %R8	1	0	0	0	0	0	0	0	0	0	0	0	0	1	0.17	N/A
MOV 0x28(%RSP),%R9	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	N/A
CMP %R9,%R8	1	0.20	0.20	0	0	0	0.20	0.20	0	0	0	0.20	0	1	0.20	scal (12.5%)
JE 4b8c <main+0x1e7c>	1	0.50	0	0	0	0	0	0.50	0	0	0	0	0	0	0.50	N/A
CMP $0x3,%R9D	1	0.20	0.20	0	0	0	0.20	0.20	0	0	0	0.20	0	1	0.20	scal (6.3%)
JBE 4c28 <main+0x1f18>	1	0.50	0	0	0	0	0	0.50	0	0	0	0	0	0	0.50	N/A
MOV %R8D,%R9D	1	0	0	0	0	0	0	0	0	0	0	0	0	1	0.17	N/A
ADD 0x98(%RSP),%R9D	1	0.20	0.20	0.33	0.33	0	0.20	0.20	0	0	0	0.20	0.33	1	0.33	N/A
SETB %R9B	1	0.50	0	0	0	0	0	0.50	0	0	0	0	0	1	0.50	N/A
OR 0x20(%RSP),%R9B	1	0.20	0.20	0.33	0.33	0	0.20	0.20	0	0	0	0.20	0.33	1-2	0.33	N/A
JE 6b47 <main+0x3e37>	1	0.50	0	0	0	0	0	0.50	0	0	0	0	0	0	0.50	N/A
CMPQ $0x3,0x98(%RSP)	1	0.20	0.20	0.33	0.33	0	0.20	0.20	0	0	0	0.20	0.33	1	0.33	scal (12.5%)
JAE 4c40 <main+0x1f30>	1	0.50	0	0	0	0	0	0.50	0	0	0	0	0	0	0.50	N/A
VXORPS %XMM0,%XMM0,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0.17	vect (25.0%)
XOR %R9D,%R9D	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0.17	N/A
JMP 4d0a <main+0x1ffa>	1	0	0	0	0	0	0	0	0	0	0	0	0	0	2.08	N/A
VXORPS %XMM0,%XMM0,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0.17	vect (25.0%)
MOV %R8,%R10	1	0	0	0	0	0	0	0	0	0	0	0	0	1	0.17	scal (12.5%)
XOR %R9D,%R9D	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0.17	N/A
MOV 0x218(%RSP),%RDX	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	scal (12.5%)
MOV 0x290(%RSP),%RAX	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	N/A
MOV 0x220(%RSP),%RDI	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	scal (12.5%)
MOV 0x288(%RSP),%RSI	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	scal (12.5%)
NOPW (%RAX,%RAX,1)	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0.17	N/A
TEST $0x3,%BL	1	0.20	0.20	0	0	0	0.20	0.20	0	0	0	0.20	0	2	0.20	N/A
JE 4be0 <main+0x1ed0>	1	0.50	0	0	0	0	0	0.50	0	0	0	0	0	0	0.50	N/A
MOV %RBX,%R10	1	0	0	0	0	0	0	0	0	0	0	0	0	1	0.17	scal (12.5%)
IMUL %R9,%R10	1	0	1	0	0	0	0	0	0	0	0	0	0	3	1	scal (12.5%)
ADD %R8,%R10	1	0.20	0.20	0	0	0	0.20	0.20	0	0	0	0.20	0	1	0.20	scal (12.5%)
ADD %ECX,%R9D	1	0.20	0.20	0	0	0	0.20	0.20	0	0	0	0.20	0	1	0.20	N/A
MOV 0x1a0(%RSP),%R11	1	0	0	0.33	0.33	0	0	0	0	0	0	0	0.33	1	0.33	scal (12.5%)
NOPL (%RAX,%RAX,1)	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0.17	N/A
JMP 4be0 <main+0x1ed0>	1	0	0	0	0	0	0	0	0	0	0	0	0	0	2.08	N/A

Report Configuration

Code clean check

Workaround

Vectorization

Details

Workaround

Execution units bottlenecks

Complex instructions

Details

Conversion instructions

Details

Workaround

Type of elements and instruction set

Matching between your loop (in the source code) and the binary loop

General properties

Front-end

Back-end

Cycles summary

Vectorization ratios

Vector efficiency ratios

Cycles and memory resources usage

Front-end bottlenecks

ASM code

Code clean check

Workaround

Vectorization

Details

Workaround

Execution units bottlenecks

Complex instructions

Details

Conversion instructions

Details

Workaround

Type of elements and instruction set

Matching between your loop (in the source code) and the binary loop

General properties

Front-end

Back-end

Cycles summary

Vectorization ratios

Vector efficiency ratios

Cycles and memory resources usage

Front-end bottlenecks

ASM code