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Unnecessary stalling on EX_rd / ID_(rs1/rs2) when rs2-value is actually an immediate #2

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KasperHesse opened this issue Feb 21, 2023 · 1 comment
Open

Unnecessary stalling on EX_rd / ID_(rs1/rs2) when rs2-value is actually an immediate #2

KasperHesse opened this issue Feb 21, 2023 · 1 comment

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@KasperHesse
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Instruction sequence

lw x4, 0(x0)
lw x5, 4(x0)

Causes a forwarding stall since the immediate in the second instruction (4) is registered as the rs2-value, even though the rs2-value is unused in LW instructions.

Solution(?): Attach flag that indicates whether rs1/rs2-values are used
@KasperHesse
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Similar issue occurs with sequence

lw x24, 4(x0)
jal x0, 0xfffffffffffc65bc

Since the jal instruction causes instr[19:15]==0x18.
Can also be solved with a flag

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@KasperHesse