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 <[email protected]>
---
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
