jit: func_line alignment for line table

The changes from 5b4457e cause the line table to have extra entries when
handling the last_error_offset. The line number from the subsequent
function is mapped to the nop instruction following the error, and as a
result, the line table suggests that the line is mapped in the former
and current range.

As an example, if you enable logging in jit-reader.c, and look for
sets.erl, you would see something like:

```
Add range `sets:new/0-CodeInfoPrologue` (0x7f5fddf03f18, 0x7f5fddf03f48), 0 lines
Add range `sets:new/0` (0x7f5fddf03f48, 0x7f5fddf04008), 3 lines
        sets.erl:170
        sets.erl:171
        sets.erl:177
Add range `sets:new/1-CodeInfoPrologue` (0x7f5fddf04008, 0x7f5fddf04038), 0 lines
Add range `sets:new/1` (0x7f5fddf04038, 0x7f5fddf04118), 2 lines
        sets.erl:177
        sets.erl:180
```

which shows that line 177 is included twice, despite only being for
sets:new/1. This can also be identified by using this GDB command:
`maintenance info line-table sets.erl`.

Move func_line back after the func label and emit the last error nop
before the label. This ensures that the line is within the (possibly
aligned) func range.

erts/emulator/beam/jit/arm/beam_asm.hpp

@@ -1401,6 +1401,10 @@ class BeamModuleAssembler : public BeamAssembler,
      * the current code position is unreachable. */
     void flush_pending_labels();
 
+    /* Move past the `last_error_offset` if necessary for the next instruction
+     * to be properly aligned (e.g. for line mappings). */
+    void flush_last_error();
+
     /* Calls the given shared fragment, ensuring that the redzone is unused and
      * that the return address forms a valid CP. */
     template<typename Any>

erts/emulator/beam/jit/arm/beam_asm_module.cpp

@@ -376,6 +376,11 @@ void BeamModuleAssembler::emit_aligned_label(const ArgLabel &Label,
     emit_label(Label);
 }
 
+void BeamModuleAssembler::emit_i_func_label(const ArgLabel &Label) {
+    flush_last_error();
+    emit_aligned_label(Label, ArgVal(ArgVal::Word, sizeof(UWord)));
+}
+
 void BeamModuleAssembler::emit_on_load() {
     on_load = current_label;
 }
@@ -430,22 +435,12 @@ void BeamModuleAssembler::emit_int_code_end() {
 void BeamModuleAssembler::emit_line(const ArgWord &Loc) {
     /* There is no need to align the line instruction. In the loaded code, the
      * type of the pointer will be void* and that pointer will only be used in
-     * comparisons.
-     *
-     * We only need to do something when there's a possibility of raising an
-     * exception at the very end of the preceding instruction (and thus
-     * pointing at the start of this one). If we were to do nothing, the error
-     * would erroneously refer to this instead of the preceding line.
-     *
-     * Since line addresses are taken _after_ line instructions we can avoid
-     * this by adding a nop when we detect this condition. */
-    if (a.offset() == last_error_offset) {
-        a.nop();
-    }
+     * comparisons. */
+
+    flush_last_error();
 }
 
 void BeamModuleAssembler::emit_func_line(const ArgWord &Loc) {
-    emit_line(Loc);
 }
 
 void BeamModuleAssembler::emit_empty_func_line() {
@@ -823,3 +818,16 @@ void BeamModuleAssembler::emit_constant(const Constant &constant) {
         }
     }
 }
+
+void BeamModuleAssembler::flush_last_error() {
+    /* When there's a possibility of raising an exception at the very end of the
+     * preceding instruction (and thus pointing at the start of this one) and
+     * this instruction has a new line registered, the error would erroneously
+     * refer to this instead of the preceding line.
+     *
+     * By adding a nop when we detect this condition, the error will correctly
+     * refer to the preceding line. */
+    if (a.offset() == last_error_offset) {
+        a.nop();
+    }
+}

erts/emulator/beam/jit/arm/ops.tab

@@ -42,12 +42,15 @@ label L
 
 # An label aligned to a certain boundary. This is used in two cases:
 #
-# * When the label points to the start of a function, as the ErtsCodeInfo
-#   struct must be word-aligned.
+# * When the label points to the start of a function. See `i_func_label`.
 # * When the address is stored on the stack or otherwise needs to be properly
 #   tagged as a continuation pointer.
 aligned_label L t
 
+# A label indicating the start of a function. The label is word-aligned as is
+# required by the ErtsCodeInfo struct.
+i_func_label L
+
 i_func_info I a a I
 int_code_end
 nif_start
@@ -903,8 +906,8 @@ int_func_start Func_Label Func_Line M F A |
   func_prologue Entry_Label Entry_Line |
   is_mfa_bif(M, F, A) =>
     i_flush_stubs |
+    i_func_label Func_Label |
     func_line Func_Line |
-    aligned_label Func_Label u=8 |
     i_func_info Func_Label M F A |
       aligned_label Entry_Label u=4 |
       i_breakpoint_trampoline |
@@ -914,8 +917,8 @@ int_func_start Func_Label Func_Line M F A |
 int_func_start Func_Label Func_Line M F A |
   func_prologue Entry_Label Entry_Line =>
     i_flush_stubs |
+    i_func_label Func_Label |
     func_line Func_Line |
-    aligned_label Func_Label u=8 |
     i_func_info Func_Label M F A |
       aligned_label Entry_Label u=4 |
       i_breakpoint_trampoline |

erts/emulator/beam/jit/asm_load.c

@@ -505,7 +505,8 @@ int beam_load_emit_op(LoaderState *stp, BeamOp *tmp_op) {
             break;
         case 'L': /* Define label */
             ASSERT(stp->specific_op == op_label_L ||
-                   stp->specific_op == op_aligned_label_Lt);
+                   stp->specific_op == op_aligned_label_Lt ||
+                   stp->specific_op == op_i_func_label_L);
             BeamLoadVerifyTag(stp, tag, TAG_u);
             stp->last_label = curr->val;
             if (stp->last_label < 0 ||

erts/emulator/beam/jit/x86/beam_asm.hpp

@@ -1424,6 +1424,10 @@ class BeamModuleAssembler : public BeamAssembler,
      * appropriate address before jumping there. */
     const Label &resolve_fragment(void (*fragment)());
 
+    /* Move past the `last_error_offset` if necessary for the next instruction
+     * to be properly aligned (e.g. for line mappings). */
+    void flush_last_error();
+
     void safe_fragment_call(void (*fragment)()) {
         emit_assert_redzone_unused();
         a.call(resolve_fragment(fragment));

erts/emulator/beam/jit/x86/beam_asm_module.cpp

@@ -342,6 +342,11 @@ void BeamModuleAssembler::emit_aligned_label(const ArgLabel &Label,
     emit_label(Label);
 }
 
+void BeamModuleAssembler::emit_i_func_label(const ArgLabel &Label) {
+    flush_last_error();
+    emit_aligned_label(Label, ArgVal(ArgVal::Word, sizeof(UWord)));
+}
+
 void BeamModuleAssembler::emit_on_load() {
     on_load = current_label;
 }
@@ -362,22 +367,12 @@ void BeamModuleAssembler::emit_int_code_end() {
 void BeamModuleAssembler::emit_line(const ArgWord &Loc) {
     /* There is no need to align the line instruction. In the loaded code, the
      * type of the pointer will be void* and that pointer will only be used in
-     * comparisons.
-     *
-     * We only need to do something when there's a possibility of raising an
-     * exception at the very end of the preceding instruction (and thus
-     * pointing at the start of this one). If we were to do nothing, the error
-     * would erroneously refer to this instead of the preceding line.
-     *
-     * Since line addresses are taken _after_ line instructions we can avoid
-     * this by adding a nop when we detect this condition. */
-    if (a.offset() == last_error_offset) {
-        a.nop();
-    }
+     * comparisons. */
+
+    flush_last_error();
 }
 
 void BeamModuleAssembler::emit_func_line(const ArgWord &Loc) {
-    emit_line(Loc);
 }
 
 void BeamModuleAssembler::emit_empty_func_line() {
@@ -416,3 +411,16 @@ const Label &BeamModuleAssembler::resolve_fragment(void (*fragment)()) {
 
     return it->second;
 }
+
+void BeamModuleAssembler::flush_last_error() {
+    /* When there's a possibility of raising an exceptions at the very end of the
+     * preceding instruction (and thus pointing at the start of this one) and
+     * this instruction has a new line registered, the error would erroneously
+     * refer to this instead of the preceding line.
+     *
+     * By adding a nop when we detect this condition, the error will correctly
+     * refer to the preceding line. */
+    if (a.offset() == last_error_offset) {
+        a.nop();
+    }
+}

erts/emulator/beam/jit/x86/ops.tab

@@ -42,12 +42,15 @@ label L
 
 # An label aligned to a certain boundary. This is used in two cases:
 #
-# * When the label points to the start of a function, as the ErtsCodeInfo
-#   struct must be word-aligned.
+# * When the label points to the start of a function. See `i_func_label`.
 # * When the address is stored on the stack or otherwise needs to be properly
 #   tagged as a continuation pointer.
 aligned_label L t
 
+# A label indicating the start of a function. The label is word-aligned as is
+# required by the ErtsCodeInfo struct.
+i_func_label L
+
 i_func_info I a a I
 int_code_end
 nif_start
@@ -827,8 +830,8 @@ int_func_start Func_Label Func_Line M F A |
 int_func_start Func_Label Func_Line M F A |
   func_prologue Entry_Label Entry_Line |
   is_mfa_bif(M, F, A) =>
+    i_func_label Func_Label |
     func_line Func_Line |
-    aligned_label Func_Label u=8 |
     i_func_info Func_Label M F A |
       aligned_label Entry_Label u=4 |
       i_breakpoint_trampoline |
@@ -837,8 +840,8 @@ int_func_start Func_Label Func_Line M F A |
 
 int_func_start Func_Label Func_Line M F A |
   func_prologue Entry_Label Entry_Line =>
+    i_func_label Func_Label |
     func_line Func_Line |
-    aligned_label Func_Label u=8 |
     i_func_info Func_Label M F A |
       aligned_label Entry_Label u=4 |
       i_breakpoint_trampoline |