Assume clzw being executed on a register that is not sign-extended, such as for the following sequence that uses (1ULL << 63) | 392 as the operand to clzw: bseti a2, zero, 63 addi a2, a2, 392 clzw a3, a2 The correct result of clzw would be 23, but the current implementation returns -32 (as it performs a 64bit clz, which results in 0 leading zero bits, and then subtracts 32).
Fix this by changing the implementation to: 1. shift the original register up by 32 2. performs a target-length (64bit) clz 3. return 32 if no bits are set Signed-off-by: Philipp Tomsich <philipp.toms...@vrull.eu> --- Changes in v10: - New patch, fixing correctnes for clzw called on a register with undefined (as in: not properly sign-extended) upper bits. target/riscv/insn_trans/trans_rvb.c.inc | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/target/riscv/insn_trans/trans_rvb.c.inc b/target/riscv/insn_trans/trans_rvb.c.inc index 6c85c89f6d..8d29cadd20 100644 --- a/target/riscv/insn_trans/trans_rvb.c.inc +++ b/target/riscv/insn_trans/trans_rvb.c.inc @@ -349,8 +349,10 @@ GEN_TRANS_SHADD(3) static void gen_clzw(TCGv ret, TCGv arg1) { - tcg_gen_clzi_tl(ret, arg1, 64); - tcg_gen_subi_tl(ret, ret, 32); + TCGv t = tcg_temp_new(); + tcg_gen_shli_tl(t, arg1, 32); + tcg_gen_clzi_tl(ret, t, 32); + tcg_temp_free(t); } static bool trans_clzw(DisasContext *ctx, arg_clzw *a) -- 2.25.1