fixup! Optimize bsr for small operands

erlang · Aug 14, 2023 · 417e7bc · 417e7bc
1 parent be5196d
commit 417e7bc
Showing 1 changed file with 6 additions and 11 deletions.
diff --git a/erts/emulator/beam/jit/arm/instr_arith.cpp b/erts/emulator/beam/jit/arm/instr_arith.cpp
@@ -1520,23 +1520,18 @@ void BeamModuleAssembler::emit_i_bsr(const ArgLabel &Fail,
         /* Ensure that both operands are small and that the shift
          * count is positive. */
         ERTS_CT_ASSERT(_TAG_IMMED1_SMALL == _TAG_IMMED1_MASK);
-        a.and_(TMP1, lhs.reg, rhs.reg);
-        if (std::get<0>(getClampedRange(RHS)) >= 0) {
-            a.and_(TMP1, TMP1, imm(_TAG_IMMED1_MASK));
-            a.cmp(TMP1, imm(_TAG_IMMED1_SMALL));
-            a.b_ne(generic);
-        } else {
-            a.mvn(TMP1, TMP1);
-            a.tst(TMP1, imm(_TAG_IMMED1_MASK));
-            a.ccmp(rhs.reg, imm(0), imm(NZCV::kSigned), arm::CondCode::kEQ);
-            a.b_lt(generic);
-        }
+        a.ands(TMP1, rhs.reg, imm((1ull << 63) | _TAG_IMMED1_MASK));
+        a.and_(TMP1, lhs.reg, TMP1);
+        a.ccmp(TMP1, imm(_TAG_IMMED1_SMALL), imm(NZCV::kNone), arm::CondCode::kPL);
+        a.b_ne(generic);
 
+        /* Calculate shift count. */
         a.asr(TMP1, rhs.reg, imm(_TAG_IMMED1_SIZE));
         mov_imm(TMP2, 63);
         a.cmp(TMP1, TMP2);
         a.csel(TMP1, TMP1, TMP2, imm(arm::CondCode::kLE));
 
+        /* Shift right. */
         ERTS_CT_ASSERT(_TAG_IMMED1_MASK == _TAG_IMMED1_SMALL);
         a.asr(dst.reg, lhs.reg, TMP1);
         a.orr(dst.reg, dst.reg, imm(_TAG_IMMED1_SMALL));