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fix(load_unit): move flush_i branch after ldbuf_w to prevent phantom … #3309

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fix(load_unit): move flush_i branch after ldbuf_w to prevent phantom … #3309

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13 changes: 9 additions & 4 deletions core/load_unit.sv
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Original file line number Diff line number Diff line change
Expand Up @@ -156,10 +156,6 @@ module load_unit
ldbuf_flushed_d = ldbuf_flushed_q;
ldbuf_valid_d = ldbuf_valid_q;

// In case of flush, raise the flushed flag in all slots.
if (flush_i) begin
ldbuf_flushed_d = '1;
end
// Free read entry (in the case of fall-through mode, free the entry
// only if there is no pending load)
if (ldbuf_r && (!LDBUF_FALLTHROUGH || !ldbuf_w)) begin
Expand All @@ -170,6 +166,15 @@ module load_unit
ldbuf_flushed_d[ldbuf_windex] = 1'b0;
ldbuf_valid_d[ldbuf_windex] = 1'b1;
end
// In case of flush, raise the flushed flag in all slots, including any
// slot just allocated by ldbuf_w in the same cycle. This branch must
// appear after ldbuf_w so that flush_i wins the lexical priority contest
// for the newly written slot; if it appeared before, a simultaneous
// data_gnt would clear flushed_d[windex] back to 0 and the slot would
// survive the flush, later producing a phantom valid_o writeback.
if (flush_i) begin
ldbuf_flushed_d = '1;
end
end

always_ff @(posedge clk_i or negedge rst_ni) begin : ldbuf_ff
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