simx: reject RV32 shift-immediate code points with shamt[5] set - #411
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Lfan-ke wants to merge 1 commit into
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simx: reject RV32 shift-immediate code points with shamt[5] set#411Lfan-ke wants to merge 1 commit into
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The Zca spec reserves shamt[5]=1 in c.slli, c.srli and c.srai for custom extensions when XLEN=32. The decompressor expanded them anyway, producing a 32-bit shift by 32 or more — itself an illegal encoding on RV32 — instead of reporting the compressed instruction as illegal. Flag them, following the existing guard for the RV64-only c.subw and c.addw. RV64 is unaffected, where shamt[5] is a valid part of the shift amount. Signed-off-by: Leo Cheng <chengkelfan@qq.com>
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The Zca spec reserves
shamt[5]=1for custom extensions when XLEN=32:— stated for
c.slliandc.srli, withc.sraidefined analogously.rvc_decompressexpanded those code points regardless, emitting a 32-bit shift by 32 or more, which is itself an illegal encoding on RV32. This flags them instead, following the guard already used for the RV64-onlyc.subw/c.addw.Verification
rvc_decompresson the three encodings, built for each XLEN:RV64 and every
shamt[5]=0encoding are unchanged.decompressor.cppcompiles clean under-Wall -Wextra -Werrorfor both XLEN values.