diff options
| author | Philipp Tomsich <philipp.tomsich@vrull.eu> | 2021-09-11 16:00:03 +0200 |
|---|---|---|
| committer | Alistair Francis <alistair.francis@wdc.com> | 2021-10-07 08:32:47 +1000 |
| commit | 45d1749c1c32f7f44e02f267407cd6bca88fb84a (patch) | |
| tree | 9d5cbade1f0cd7d9272cb36b4ee010eef4604439 /target | |
| parent | e47fb6c1e96a4e50603c13b8408e0745a09cd867 (diff) | |
target/riscv: clwz must ignore high bits (use shift-left & changed logic)
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
Marking this instruction as 'w-form' (i.e., setting ctx->w) would not
correctly model the behaviour, as the instruction should not perform
a zero-extensions on the input (after all, it is not a .uw instruction)
and the result is always in the range 0..32 (so neither a sign-extension
nor a zero-extension on the result will ever be needed). Consequently,
we do not set ctx->w and mark the instruction as EXT_NONE.
Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
Reviewed-by: LIU Zhiwei<zhiwei_liu@c-sky.com>
Message-id: 20210911140016.834071-4-philipp.tomsich@vrull.eu
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Diffstat (limited to 'target')
| -rw-r--r-- | target/riscv/insn_trans/trans_rvb.c.inc | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/target/riscv/insn_trans/trans_rvb.c.inc b/target/riscv/insn_trans/trans_rvb.c.inc index 6c85c89f6d..73d1e45026 100644 --- a/target/riscv/insn_trans/trans_rvb.c.inc +++ b/target/riscv/insn_trans/trans_rvb.c.inc @@ -349,15 +349,17 @@ 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) { REQUIRE_64BIT(ctx); REQUIRE_EXT(ctx, RVB); - return gen_unary(ctx, a, EXT_ZERO, gen_clzw); + return gen_unary(ctx, a, EXT_NONE, gen_clzw); } static void gen_ctzw(TCGv ret, TCGv arg1) |