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[BugFix] Fix UB in per_token_group_quant.cu #24913

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Merged
merged 1 commit into from
Sep 23, 2025
Merged

[BugFix] Fix UB in per_token_group_quant.cu #24913

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6 changes: 3 additions & 3 deletions csrc/quantization/fp8/per_token_group_quant.cu
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Original file line number Diff line number Diff line change
Expand Up @@ -12,8 +12,8 @@
#include "../vectorization_utils.cuh"
#include "../../dispatch_utils.h"

__device__ __forceinline__ float GroupReduceMax(float val, const int tid) {
unsigned mask = 0xffff;
__device__ __forceinline__ float GroupReduceMax(float val) {
unsigned mask = threadIdx.x % 32 >= 16 ? 0xffff0000 : 0x0000ffff;

val = fmaxf(val, __shfl_xor_sync(mask, val, 8));
val = fmaxf(val, __shfl_xor_sync(mask, val, 4));
Expand Down Expand Up @@ -86,7 +86,7 @@ __global__ void per_token_group_quant_8bit_kernel(
threads_per_group, // stride in group
scalar_op_cache); // scalar handler

local_absmax = GroupReduceMax(local_absmax, lane_id);
local_absmax = GroupReduceMax(local_absmax);

float y_s = local_absmax / max_8bit;
if constexpr (SCALE_UE8M0) {
Expand Down