On 11/8/22 15:05, Taylor Simpson wrote:
+/* Shift left with saturation */
+static void gen_shl_sat(TCGv dst, TCGv src, TCGv shift_amt)
+{
+ TCGv_i64 src64 = tcg_temp_local_new_i64();
+ TCGv_i64 shift64 = tcg_temp_new_i64();
+ TCGv_i64 dst64 = tcg_temp_new_i64();
+ TCGv dst_sar = tcg_temp_new();
+ TCGv ovf = tcg_temp_new();
+ TCGv satval = tcg_temp_new();
+ TCGv min = tcg_constant_tl(0x80000000);
+ TCGv max = tcg_constant_tl(0x7fffffff);
+
+ /*
+ * dst64 = (int64_t)src << (int64_t)shift_amt
+ * dst = (int32_t)dst64
+ * dst_sar = dst >> shift_amt
+ * if (dst_sar != src) {
+ * usr.OVF = 1
+ * dst = src < 0 ? min : max
+ * }
+ */
+ tcg_gen_ext_i32_i64(src64, src);
+ tcg_gen_ext_i32_i64(shift64, shift_amt);
+ tcg_gen_shl_i64(dst64, src64, shift64);
+
+ tcg_gen_extrl_i64_i32(dst, dst64);
+ tcg_gen_sar_tl(dst_sar, dst, shift_amt);
I don't think this is quite right. In particular:
+static void gen_asr_r_r_sat(TCGv RdV, TCGv RsV, TCGv RtV)
+{
+ TCGv shift_amt = tcg_temp_local_new();
+ TCGLabel *positive = gen_new_label();
+ TCGLabel *done = gen_new_label();
+
+ tcg_gen_sextract_i32(shift_amt, RtV, 0, 7);
This suggests shift amounts -64 ... 63.
+ tcg_gen_brcondi_tl(TCG_COND_GE, shift_amt, 0, positive);
+
+ /* Negative shift amount => shift left */
+ tcg_gen_neg_tl(shift_amt, shift_amt);
-64 -> 64.
So! We have two out-of-range shifts in gen_shl_sat, both i64 and i32.
If we fix one, then we don't even need the extension to i64 either.
Consider
/*
* sh32 = shift & 31;
* dst = sh32 == shift ? src : 0;
* dst <<= sh32;
* dst_sar = dst >> sh32;
* if (dst_sar != src) ...
*/
tcg_gen_andi_i32(sh32, shift_amt, 31);
tcg_gen_movcond_i32(TCG_COND_EQ, dst,
sh32, shift_amt,
src, tcg_constant_i32(0));
tcg_gen_shl_i32(dst, dst, sh32);
tcg_gen_sar_i32(dst_sar, dst, sh32);
r~
