[PATCH 1/2] mips: Correct and optimize jit_rshr() and jit_rshr_u()

[Paul Cercueil]

Rework the branch-less path to shrink the size of jit_rshr() and
jit_rshr_u(), and use one register less, so that the whole code path
that uses branches can be dropped.

The case where O4 == __WORDSIZE in jit_rshr() was also handled
incorrectly, as it would zero the O1 register instead of sign-extending
it.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
---
 lib/jit_mips-cpu.c | 79 ++++++++++++++++------------------------------
 1 file changed, 27 insertions(+), 52 deletions(-)

diff --git a/lib/jit_mips-cpu.c b/lib/jit_mips-cpu.c
index e59743e..cfbcd7e 100644
--- a/lib/jit_mips-cpu.c
+++ b/lib/jit_mips-cpu.c
@@ -2425,72 +2425,47 @@ static void
 _xrshr(jit_state_t *_jit, jit_bool_t sign,
        jit_int32_t r0, jit_int32_t r1, jit_int32_t r2, jit_int32_t r3)
 {
-    jit_bool_t         branch;
-    jit_word_t         over, zero, done, done_over;
-    jit_int32_t                t0, s0, t1, s1, t2, s2, t3, s3;
+    jit_int32_t                t0, s0, t2, s2, t3, s3;
     s0 = jit_get_reg(jit_class_gpr);
     t0 = rn(s0);
     if (r0 == r2 || r1 == r2) {
-       s2 = jit_get_reg(jit_class_gpr);
-       t2 = rn(s2);
-       movr(t2, r2);
+        s2 = jit_get_reg(jit_class_gpr);
+        t2 = rn(s2);
+        movr(t2, r2);
     }
     else
-       t2 = r2;
+        t2 = r2;
     if (r0 == r3 || r1 == r3) {
-       s3 = jit_get_reg(jit_class_gpr);
-       t3 = rn(s3);
-       movr(t3, r3);
+        s3 = jit_get_reg(jit_class_gpr);
+        t3 = rn(s3);
+        movr(t3, r3);
     }
     else
-       t3 = r3;
-    if ((s1 = jit_get_reg(jit_class_gpr|jit_class_nospill|jit_class_chk))) {
-       t1 = rn(s1);
-       branch = 0;
+        t3 = r3;
+
+    if (sign) {
+        /* underflow? */
+        eqi(t0, t3, __WORDSIZE);
+        subr(t0, t3, t0);
+        rshr(r0, t2, t0);
+    } else {
+        /* underflow? */
+        nei(t0, t3, __WORDSIZE);
+        rshr_u(r0, t2, t3);
+        movzr(r0, t0, t0);
     }
-    else
-       branch = 1;
+
     rsbi(t0, t3, __WORDSIZE);
-    if (sign)
-       rshr(r0, t2, t3);
-    else
-       rshr_u(r0, t2, t3);
     lshr(r1, t2, t0);
-    if (branch) {
-       zero = beqi(_jit->pc.w, t3, 0);
-       over = beqi(_jit->pc.w, t3, __WORDSIZE);
-       done = jmpi(_jit->pc.w, 1);
-       flush();
-       patch_at(over, _jit->pc.w);
-       /* underflow */
-       if (sign)
-           rshi(r0, t2, __WORDSIZE - 1);
-       else
-           movi(r0, 0);
-       done_over = jmpi(_jit->pc.w, 1);
-       /* zero */
-       flush();
-       patch_at(zero, _jit->pc.w);
-       movi(r1, 0);
-       flush();
-       patch_at(done, _jit->pc.w);
-       patch_at(done_over, _jit->pc.w);
-       jit_unget_reg(s1);
-    }
-    else {
-       /* zero? */
-       movi(t0, 0);
-       movzr(r1, t0, t3);
-       /* underflow? */
-       eqi(t1, t3, __WORDSIZE);
-       movnr(r0, t0, t1);
-       jit_unget_reg(s1);
-    }
+
+    /* zero? */
+    movzr(r1, t3, t3);
+
     jit_unget_reg(s0);
     if (t2 != r2)
-       jit_unget_reg(s2);
+        jit_unget_reg(s2);
     if (t3 != r3)
-       jit_unget_reg(s3);
+        jit_unget_reg(s3);
 }
 
 static void
-- 
2.40.1