[DebugInfo] Flang should generate debug location for limited instruct…

…ions in prolog (#940)

* Flang should not generate debug location for instructions in prolog

Due to this wrong debug_line section entry is created with wrong instruction
marked as 'prologue_end'. More details in commited test cases.

* Minor modifications are done.

- to match coding style of newly added functions to rest of the file.
- to reduce optimization option to -O0 in test case.

test/debug_info/dwarfdump_prolog.f90

@@ -0,0 +1,30 @@
+!RUN: %flang -g -O0 %s -o %t
+!RUN: llvm-dwarfdump  --debug-line %t -o - | FileCheck %s
+
+!CHECK: name: "dwarfdump_prolog.f90"
+!CHECK: Address            Line   Column File   ISA Discriminator Flags
+!CHECK: {{0x[0-9a-f]+}}     13      1      1   0             0  is_stmt prologue_end
+!CHECK: {{0x[0-9a-f]+}}     29      1      1   0             0  is_stmt prologue_end
+
+subroutine show (message, array)
+  character (len=*) :: message
+  integer :: array(:)
+
+  print *, message
+  print *, array
+
+end subroutine show
+
+program prolog
+
+  interface
+     subroutine show (message, array)
+       character (len=*) :: message
+       integer :: array(:)
+     end subroutine show
+  end interface
+
+  integer :: array(10) = (/1,2,3,4,5,6,7,8,9,10/)
+
+  call show ("array", array)
+end program prolog

test/debug_info/prolog.f90

@@ -0,0 +1,37 @@
+!RUN: %flang -g -S -emit-llvm %s -o - | FileCheck %s
+
+! check non debug instructions should not have debug location
+!CHECK: define void @show_
+!CHECK: call void @llvm.dbg.declare
+!CHECK-SAME: , !dbg {{![0-9]+}}
+!CHECK-NOT: bitcast i64* %"array$sd" to i8*, !dbg
+!CHECK: store i64 {{%[0-9]+}}, i64* %z_b_3_{{[0-9]+}}, align 8
+!CHECK: br label
+!CHECK: ret void, !dbg {{![0-9]+}}
+subroutine show (message, array)
+  character (len=*) :: message
+  integer :: array(:)
+
+  print *, message
+  print *, array
+
+end subroutine show
+
+!CHECK: define void @MAIN_
+!CHECK-NOT: bitcast void (...)* @fort_init to void (i8*, ...)*, !dbg {{![0-9]+}}
+!CHECK: call void @llvm.dbg.declare
+!CHECK-SAME: , !dbg {{![0-9]+}}
+!CHECK: ret void, !dbg
+program prolog
+
+  interface
+     subroutine show (message, array)
+       character (len=*) :: message
+       integer :: array(:)
+     end subroutine show
+  end interface
+
+  integer :: array(10) = (/1,2,3,4,5,6,7,8,9,10/)
+
+  call show ("array", array)
+end program prolog

tools/flang2/flang2exe/cgmain.cpp

@@ -2794,6 +2794,41 @@ write_verbose_type(LL_Type *ll_type)
   print_token(ll_type->str);
 }
 
+/* whether debug location should be suppressed */
+static bool
+should_suppress_debug_loc(INSTR_LIST *instrs)
+{
+  if (!instrs)
+    return false;
+
+  // return true if not a call instruction
+  switch (instrs->i_name) {
+  case I_INVOKE:
+    return false;
+  case I_CALL:
+    // f90 runtime functions fort_init and f90_* dont need debug location
+    if (instrs->prev && (instrs->operands->ot_type == OT_TMP) &&
+        (instrs->operands->tmps == instrs->prev->tmps) &&
+        (instrs->prev->operands->ot_type == OT_VAR)) {
+      // We dont need to expose those internals in prolog to user
+      // %1 = bitcast void (...)* @fort_init to void (i8*, ...)*
+      // call void (i8*, ...) %1(i8* %0)
+      // %8 = bitcast void (...)* @f90_template1_i8 to void (i8*, i8*, i8*, i8*,
+      //      i8*, i8*, ...)*
+      // call void (i8*, i8*, i8*, i8*, i8*, i8*, ...) %8(i8*
+      //      %2, i8* %3, i8* %4, i8* %5, i8* %6, i8* %7)
+
+      if (char *name_str = instrs->prev->operands->string) {
+        return (!strncmp(name_str, "@fort_init", strlen("@fort_init")) ||
+                !strncmp(name_str, "@f90_", strlen("@f90_")));
+      }
+    }
+    return false;
+  default:
+    return true;
+  }
+}
+
 /**
    \brief Write the instruction list to the LLVM IR output file
  */
@@ -3328,8 +3363,17 @@ write_instructions(LL_Module *module)
                ERR_Fatal);
       }
     }
-    if (!ISNVVMCODEGEN &&
-        (!LL_MDREF_IS_NULL(instrs->dbg_line_op) && !dbg_line_op_written)) {
+    /*
+     *  Do not dump debug location here if
+     *  - it is NULL
+     *  - it is already written (dbg_line_op_written) or
+     *  - it is a known internal (f90 runtime) call in prolog (fort_init &
+     * f90_*)
+     */
+    if (!(LL_MDREF_IS_NULL(instrs->dbg_line_op) || dbg_line_op_written ||
+          ((instrs->dbg_line_op ==
+            lldbg_get_subprogram_line(module->debug_info)) &&
+           should_suppress_debug_loc(instrs)))) {
       print_dbg_line(instrs->dbg_line_op);
     }
 #if DEBUG

tools/flang2/flang2exe/lldebug.cpp

@@ -129,6 +129,7 @@ struct LL_DebugInfo {
   LL_MDRef cur_module_mdnode;
   LL_MDRef cur_cmnblk_mdnode;
   int cur_subprogram_lineno;
+  LL_MDRef cur_subprogram_line_mdnode;
   LL_MDRef cur_subprogram_null_loc;
   LL_MDRef cur_line_mdnode;
   PARAMINFO param_stack[PARAM_STACK_SIZE];
@@ -2161,8 +2162,10 @@ lldbg_emit_subprogram(LL_DebugInfo *db, SPTR sptr, DTYPE ret_dtype, int findex,
                                db->import_entity_list->entity_type);
     db->import_entity_list = db->import_entity_list->next;
   }
-    db->cur_subprogram_null_loc =
-        lldbg_create_location_mdnode(db, 0, 0, db->cur_subprogram_mdnode);
+  db->cur_subprogram_null_loc =
+      lldbg_create_location_mdnode(db, 0, 0, db->cur_subprogram_mdnode);
+  db->cur_subprogram_lineno = lineno;
+  db->cur_subprogram_line_mdnode = ll_get_md_null();
   db->param_idx = 0;
   memset(db->param_stack, 0, sizeof(PARAMINFO) * PARAM_STACK_SIZE);
   lldbg_emit_lexical_blocks(db, sptr, findex, targetNVVM);
@@ -2306,6 +2309,10 @@ lldbg_emit_line(LL_DebugInfo *db, int lineno)
       db->cur_line_mdnode =
           lldbg_create_location_mdnode(db, lineno, 1, db->blk_tab[idx].mdnode);
     }
+    // it is not yet column aware so comparing only line
+    if (lineno == db->cur_subprogram_lineno)
+      db->cur_subprogram_line_mdnode = db->cur_line_mdnode;
+
     last_line = lineno;
   }
 }
@@ -3529,3 +3536,8 @@ new_debug_name(const char *str1, const char *str2, const char *str3)
   return (const char *)new_name;
 }
 
+LL_MDRef
+lldbg_get_subprogram_line(LL_DebugInfo *db)
+{
+  return db->cur_subprogram_line_mdnode;
+}

tools/flang2/flang2exe/lldebug.h

@@ -273,4 +273,6 @@ void InitializeDIFlags(const LL_IRFeatures *feature);
 
 void lldbg_reset_module(LL_DebugInfo *db);
 
+/// \brief Get the debug location mdnode of the current procedure.
+LL_MDRef lldbg_get_subprogram_line(LL_DebugInfo *db);
 #endif /* LLDEBUG_H_ */