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Add comment for why opt_expr is necessary

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Eddie Hung 2019-09-10 14:11:56 -07:00
parent 8514e7c32e
commit f3a55d3f06
1 changed files with 2 additions and 0 deletions
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techlibs/xilinx/synth_xilinx.cc
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@ -325,6 +325,8 @@ struct SynthXilinxPass : public ScriptPass
if (!nodsp || help_mode) { if (!nodsp || help_mode) {
// NB: Xilinx multipliers are signed only // NB: Xilinx multipliers are signed only
run("techmap -map +/mul2dsp.v -map +/xilinx/dsp_map.v -D DSP_A_MAXWIDTH=25 -D DSP_A_MAXWIDTH_PARTIAL=18 -D DSP_B_MAXWIDTH=18 -D DSP_SIGNEDONLY=1 -D DSP_NAME=$__MUL25X18", "(skip if '-nodsp')"); run("techmap -map +/mul2dsp.v -map +/xilinx/dsp_map.v -D DSP_A_MAXWIDTH=25 -D DSP_A_MAXWIDTH_PARTIAL=18 -D DSP_B_MAXWIDTH=18 -D DSP_SIGNEDONLY=1 -D DSP_NAME=$__MUL25X18", "(skip if '-nodsp')");
// Necessary for optimising away $shl cells, as well as $add cells
// that have inputs with 1'b0 LSBs
run("opt_expr -fine", " (skip if '-nodsp')"); run("opt_expr -fine", " (skip if '-nodsp')");
run("wreduce", " (skip if '-nodsp')"); run("wreduce", " (skip if '-nodsp')");
run("xilinx_dsp", " (skip if '-nodsp')"); run("xilinx_dsp", " (skip if '-nodsp')");