Add annotations for likely/unlikely

In a correct Erlang programs, we can expect that:

* A GC test instruction (such as test_heap) is more likely
  not to do the GC.
* A BIF is more likely to succeed than to fail.
* A BIF is more likely to fail in a guard than in a body.
* An apply or fun call is likely to succeed.

Annotate conditions accordingly.

3 files changed, 33 insertions, 27 deletions

diff --git a/erts/emulator/beam/bif_instrs.tab b/erts/emulator/beam/bif_instrs.tab
index 5aa0523e06..3c95113907 100644
--- a/erts/emulator/beam/bif_instrs.tab
+++ b/erts/emulator/beam/bif_instrs.tab
@@ -45,7 +45,7 @@ CALL_GUARD_BIF(BF, TmpReg, Dst) {
     ERTS_HOLE_CHECK(c_p);
     FCALLS = c_p->fcalls;
     ERTS_DBG_CHK_REDS(c_p, FCALLS);
-    if (is_value(result)) {
+    if (ERTS_LIKELY(is_value(result))) {
         $Dst = result;
         $NEXT0();
     }
@@ -145,12 +145,12 @@ i_gc_bif1(Fail, Bif, Src, Live, Dst) {
     ERTS_HOLE_CHECK(c_p);
     FCALLS = c_p->fcalls;
     ERTS_DBG_CHK_REDS(c_p, FCALLS);
-    if (is_value(result)) {
+    if (ERTS_LIKELY(is_value(result))) {
         $REFRESH_GEN_DEST();
         $Dst = result;
         $NEXT0();
     }
-    if ($Fail != 0) {          /* Handle error in guard. */
+    if (ERTS_LIKELY($Fail != 0)) { /* Handle error in guard. */
         $NEXT($Fail);
     }
 
@@ -195,13 +195,13 @@ i_gc_bif2(Fail, Bif, Live, Src1, Src2, Dst) {
     ERTS_HOLE_CHECK(c_p);
     FCALLS = c_p->fcalls;
     ERTS_DBG_CHK_REDS(c_p, FCALLS);
-    if (is_value(result)) {
+    if (ERTS_LIKELY(is_value(result))) {
         $REFRESH_GEN_DEST();
         $Dst = result;
         $NEXT0();
     }
 
-    if ($Fail != 0) {          /* Handle error in guard. */
+    if (ERTS_LIKELY($Fail != 0)) { /* Handle error in guard. */
         $NEXT($Fail);
     }
 
@@ -249,14 +249,14 @@ i_gc_bif3(Fail, Bif, Live, Src2, Src3, Dst) {
     ERTS_HOLE_CHECK(c_p);
     FCALLS = c_p->fcalls;
     ERTS_DBG_CHK_REDS(c_p, FCALLS);
-    if (is_value(result)) {
+    if (ERTS_LIKELY(is_value(result))) {
         $REFRESH_GEN_DEST();
         $Dst = result;
         $NEXT0();
     }
 
     /* Handle error in guard. */
-    if ($Fail != 0) {
+    if (ERTS_LIKELY($Fail != 0)) {
         $NEXT($Fail);
     }
 
@@ -325,7 +325,7 @@ call_bif(Exp) {
         ERTS_MSACC_UPDATE_CACHE_X();
     }
     ERTS_MSACC_SET_STATE_CACHED_M_X(ERTS_MSACC_STATE_EMULATOR);
-    if (is_value(result)) {
+    if (ERTS_LIKELY(is_value(result))) {
         r(0) = result;
         CHECK_TERM(r(0));
         $NEXT0();
@@ -370,7 +370,7 @@ send() {
     PROCESS_MAIN_CHK_LOCKS(c_p);
     HTOP = HEAP_TOP(c_p);
     FCALLS = c_p->fcalls;
-    if (is_value(result)) {
+    if (ERTS_LIKELY(is_value(result))) {
         r(0) = result;
         CHECK_TERM(r(0));
     } else if (c_p->freason == TRAP) {
@@ -520,7 +520,7 @@ nif_bif.epilogue() {
     SWAPIN;  /* There might have been a garbage collection. */
     FCALLS = c_p->fcalls;
     ERTS_DBG_CHK_REDS(c_p, FCALLS);
-    if (is_value(nif_bif_result)) {
+    if (ERTS_LIKELY(is_value(nif_bif_result))) {
         r(0) = nif_bif_result;
         CHECK_TERM(r(0));
         SET_I(c_p->cp);
diff --git a/erts/emulator/beam/instrs.tab b/erts/emulator/beam/instrs.tab
index 1af01e53bd..58432cbbb4 100644
--- a/erts/emulator/beam/instrs.tab
+++ b/erts/emulator/beam/instrs.tab
@@ -171,7 +171,7 @@ HANDLE_APPLY_ERROR() {
 i_apply() {
     BeamInstr *next;
     $APPLY(NULL, 0);
-    if (next != NULL) {
+    if (ERTS_LIKELY(next != NULL)) {
         $i_call(next);
     }
     $HANDLE_APPLY_ERROR();
@@ -180,7 +180,7 @@ i_apply() {
 i_apply_last(Deallocate) {
     BeamInstr *next;
     $APPLY(I, $Deallocate);
-    if (next != NULL) {
+    if (ERTS_LIKELY(next != NULL)) {
         $i_call_last(next, $Deallocate);
     }
     $HANDLE_APPLY_ERROR();
@@ -189,7 +189,7 @@ i_apply_last(Deallocate) {
 i_apply_only() {
     BeamInstr *next;
     $APPLY(I, 0);
-    if (next != NULL) {
+    if (ERTS_LIKELY(next != NULL)) {
         $i_call_only(next);
     }
     $HANDLE_APPLY_ERROR();
@@ -205,7 +205,7 @@ FIXED_APPLY(Arity, I, Deallocate) {
 apply(Arity) {
     BeamInstr *next;
     $FIXED_APPLY($Arity, NULL, 0);
-    if (next != NULL) {
+    if (ERTS_LIKELY(next != NULL)) {
         $i_call(next);
     }
     $HANDLE_APPLY_ERROR();
@@ -214,7 +214,7 @@ apply(Arity) {
 apply_last(Arity, Deallocate) {
     BeamInstr *next;
     $FIXED_APPLY($Arity, I, $Deallocate);
-    if (next != NULL) {
+    if (ERTS_LIKELY(next != NULL)) {
         $i_call_last(next, $Deallocate);
     }
     $HANDLE_APPLY_ERROR();
@@ -238,7 +238,7 @@ DISPATCH_FUN(I) {
 i_apply_fun() {
     BeamInstr *next;
     $APPLY_FUN();
-    if (next != NULL) {
+    if (ERTS_LIKELY(next != NULL)) {
         SET_CP(c_p, $NEXT_INSTRUCTION);
         $DISPATCH_FUN(next);
     }
@@ -248,7 +248,7 @@ i_apply_fun() {
 i_apply_fun_last(Deallocate) {
     BeamInstr *next;
     $APPLY_FUN();
-    if (next != NULL) {
+    if (ERTS_LIKELY(next != NULL)) {
         $deallocate($Deallocate);
         $DISPATCH_FUN(next);
     }
@@ -258,7 +258,7 @@ i_apply_fun_last(Deallocate) {
 i_apply_fun_only() {
     BeamInstr *next;
     $APPLY_FUN();
-    if (next != NULL) {
+    if (ERTS_LIKELY(next != NULL)) {
         $DISPATCH_FUN(next);
     }
     $HANDLE_APPLY_FUN_ERROR();
@@ -274,7 +274,7 @@ CALL_FUN(Fun) {
 i_call_fun(Fun) {
     BeamInstr *next;
     $CALL_FUN($Fun);
-    if (next != NULL) {
+    if (ERTS_LIKELY(next != NULL)) {
         SET_CP(c_p, $NEXT_INSTRUCTION);
         $DISPATCH_FUN(next);
     }
@@ -284,7 +284,7 @@ i_call_fun(Fun) {
 i_call_fun_last(Fun, Deallocate) {
     BeamInstr *next;
     $CALL_FUN($Fun);
-    if (next != NULL) {
+    if (ERTS_LIKELY(next != NULL)) {
         $deallocate($Deallocate);
         $DISPATCH_FUN(next);
     }
@@ -378,7 +378,7 @@ element_group.fetch(Src) {
 
 element_group.execute(Fail, Index, Dst) {
     element_index = $Index;
-    if (is_small(element_index) && is_tuple(element_tuple)) {
+    if (ERTS_LIKELY(is_small(element_index) && is_tuple(element_tuple))) {
         Eterm* tp = tuple_val(element_tuple);
 
         if ((signed_val(element_index) >= 1) &&
@@ -402,7 +402,7 @@ fast_element_group.fetch(Src) {
 }
 
 fast_element_group.execute(Fail, Index, Dst) {
-    if (is_tuple(fast_element_tuple)) {
+    if (ERTS_LIKELY(is_tuple(fast_element_tuple))) {
         Eterm* tp = tuple_val(fast_element_tuple);
         Eterm pos = $Index;	/* Untagged integer >= 1 */
         if (pos <= arityval(*tp)) {
diff --git a/erts/emulator/beam/macros.tab b/erts/emulator/beam/macros.tab
index 41dc761e90..bac96be7d3 100644
--- a/erts/emulator/beam/macros.tab
+++ b/erts/emulator/beam/macros.tab
@@ -42,7 +42,7 @@ JUMP(Fail) {
 
 GC_TEST(Ns, Nh, Live) {
     Uint need = $Nh + $Ns;
-    if (E - HTOP < need) {
+    if (ERTS_UNLIKELY(E - HTOP < need)) {
        SWAPOUT;
        PROCESS_MAIN_CHK_LOCKS(c_p);
        FCALLS -= erts_garbage_collect_nobump(c_p, need, reg, $Live, FCALLS);
@@ -55,7 +55,7 @@ GC_TEST(Ns, Nh, Live) {
 
 GC_TEST_PRESERVE(NeedHeap, Live, PreserveTerm) {
     Uint need = $NeedHeap;
-    if (E - HTOP < need) {
+    if (ERTS_UNLIKELY(E - HTOP < need)) {
        SWAPOUT;
        reg[$Live] = $PreserveTerm;
        PROCESS_MAIN_CHK_LOCKS(c_p);
@@ -99,7 +99,13 @@ FAIL_BODY() {
 
 FAIL_HEAD_OR_BODY(Fail) {
     //| -no_prefetch
-    if ($Fail) {
+
+    /*
+     * In a correctly working program, we expect failures in
+     * guards to be more likely than failures in bodies.
+     */
+
+    if (ERTS_LIKELY($Fail)) {
         $FAIL($Fail);
     }
     goto find_func_info;
@@ -122,7 +128,7 @@ SYSTEM_LIMIT(Fail) {
 
 BIF_ERROR_ARITY_1(Fail, BIF, Op1) {
     //| -no_prefetch
-    if ($Fail) {
+    if (ERTS_LIKELY($Fail)) {
         $FAIL($Fail);
     }
     reg[0] = $Op1;
@@ -133,7 +139,7 @@ BIF_ERROR_ARITY_1(Fail, BIF, Op1) {
 
 BIF_ERROR_ARITY_2(Fail, BIF, Op1, Op2) {
     //| -no_prefetch
-    if ($Fail) {
+    if (ERTS_LIKELY($Fail)) {
         $FAIL($Fail);
     }
     reg[0] = $Op1;