ggml-cpu : fix rms_norm_back wrong output under in-place aliasing#24305
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ggerganov
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…ml-org#24305) * ggml-cpu : fix rms_norm_back wrong output under in-place aliasing * cont : clean-up comment --------- Co-authored-by: Georgi Gerganov <ggerganov@gmail.com> (cherry picked from commit fd3271e)
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Overview
ggml_compute_forward_rms_norm_back_f32could produce wrong results when the destination aliases an input.GGML_OP_RMS_NORM_BACKis listed inggml_op_can_inplace, so the scheduler may reusesrc0(dz) orsrc1(x)'s buffer fordx. The old multi-stepcpy/scale/acc/scalesequence overwrote that buffer in thedx := xstep and then re-read it in the+= dzstep. This replaces it with a single fused read-before-write loop, which is safe under either aliasing.Additional information
Requested by @ggerganov in ggml-org/ggml#1519, where I originally reported and fixed this (#1491). Submitting the single ops.cpp change here as asked; no regression test per that thread. Built
ggml-cpulocally on macOS to confirm it compiles.Requirements