fixup! Optimize bsr for small operands

erlang · Aug 14, 2023 · 36c0ff3 · 36c0ff3
1 parent b78544f
commit 36c0ff3
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Showing 2 changed files with 24 additions and 9 deletions.
diff --git a/erts/emulator/beam/jit/arm/instr_arith.cpp b/erts/emulator/beam/jit/arm/instr_arith.cpp
@@ -1519,11 +1519,19 @@ void BeamModuleAssembler::emit_i_bsr(const ArgLabel &Fail,
 
         /* Ensure that both operands are small and that the shift
          * count is positive. */
-        a.and_(TMP1, lhs.reg, rhs.reg);
-        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);
+        if (std::get<0>(getClampedRange(RHS)) >= 0) {
+            ERTS_CT_ASSERT(_TAG_IMMED1_SMALL == _TAG_IMMED1_MASK);
+            a.and_(TMP1, lhs.reg, rhs.reg);
+            a.and_(TMP1, TMP1, imm(_TAG_IMMED1_MASK));
+            a.cmp(TMP1, imm(_TAG_IMMED1_SMALL));
+            a.b_ne(generic);
+        } else {
+            a.and_(TMP1, lhs.reg, rhs.reg);
+            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.asr(TMP1, rhs.reg, imm(_TAG_IMMED1_SIZE));
         mov_imm(TMP2, 63);

diff --git a/erts/emulator/test/small_SUITE.erl b/erts/emulator/test/small_SUITE.erl
@@ -1069,7 +1069,8 @@ test_bsr(_Config) ->
     Fs0 = gen_func_names(Pairs, 0),
     Fs = [gen_bsr_function(F) || F <- Fs0],
     Tree = ?Q(["-module('@Mod@').",
-               "-compile([export_all,nowarn_export_all])."]) ++ Fs,
+               "-compile([export_all,nowarn_export_all]).",
+               "id(I) -> I."]) ++ Fs,
     %% merl:print(Tree),
     {ok,_Bin} = merl:compile_and_load(Tree, []),
     test_bsr(Fs0, Mod),
@@ -1107,12 +1108,18 @@ gen_bsr_function({Name,{N,S}}) ->
                    Res
            end;
         '@Name@'(N0, S, More) ->
-           Res = N0 bsr S,
+           Res = id(N0 bsr S),
            if
                More ->
                    N = N0 band _@Mask@,
-                   Res = N0 bsr S,
-                   Res = N bsr S;
+                   Res = id(N0 bsr S),
+                   Res = id(N bsr S),
+                   if
+                      S >= 0 ->
+                          Res = id(N bsr S);
+                      true ->
+                           Res
+                   end;
                true ->
                    Res
            end. ").