Add support for GNU loop pragmas [GH #174]

Author: mborland

doc/source/code_style.rst

@@ -707,3 +707,16 @@ instead of:
 .. code:: cpp
 
    f(a, b, c, d, /*is_foo_bar=*/FALSE, /*needs_more_squirrels=*/VERY_FALSE);
+
+Wrapping Array Subscripts
+-------------------------
+
+Array subscripts that cause the line length to exceed 79 characters are
+wrapped like a function call whose argument cannot fit: the line is broken
+after the "``[``" and the continuation is right-aligned to column 79, including
+the closing "``]``" and any punctuation that follows it:
+
+.. code:: cpp
+
+   pkdp = pragma_description_for_pragma_kind[
+                     /* something very long (right-aligned to column 79) */];

src/Changes

@@ -1,5 +1,23 @@
 Version 7.1
 
+10/21/26  [GH #174]
+C-generating back end: placement of GCC loop pragmas
+
+The GCC loop pragmas "#pragma GCC unroll", "#pragma GCC ivdep", and
+"#pragma GCC novector" were previously recorded in the IL as pragmas of the
+enclosing block and so were emitted by the C-generating back end at the start
+of that block, rather than immediately in front of the loop to which they
+apply.  The back-end compiler then rejected the generated code.  For example:
+
+  void h();
+  void f(char *first, char *last) {
+    h();
+  #pragma GCC unroll 4    // Previously emitted in front of the call of h,
+    while (first != last) // causing a "for, while or do statement expected"
+      ++first;            // error from the back-end compiler.
+  }
+
+
 10/21/26 [GH #335]
 Type transformations of qualified function types
 

src/il_alloc.c

@@ -4475,6 +4475,7 @@ pointer to it.
 #if GNU_EXTENSIONS_ALLOWED
     case pk_gcc_immediate:
     case pk_gcc_next_token:
+    case pk_gcc_next_statement:
       clear_gcc_pragma_descr(&pp->variant.gcc);
       break;
 #if GNU_VECTOR_TYPES_ALLOWED && BUILTIN_FUNCTIONS_ENABLED

src/il_def.h

@@ -6723,6 +6723,7 @@ enum a_pragma_kind : a_byte {
 #if GNU_EXTENSIONS_ALLOWED
   pk_gcc_immediate,     /* GCC pragmas (handled immediately). */
   pk_gcc_next_token,    /* GCC pragmas (handled as next token). */
+  pk_gcc_next_statement,/* GCC pragmas (bound to the next statement). */
 #if GNU_VECTOR_TYPES_ALLOWED && BUILTIN_FUNCTIONS_ENABLED
   pk_gnu_riscv,         /* GCC RISC-V intrinsics. */
   pk_clang_riscv,       /* Clang RISC-V intrinsics. */
@@ -6834,6 +6835,7 @@ EXTERN_CONSTINIT_ARRAY(a_const_char*, pragma_ids, pk_last + 1)
 #if GNU_EXTENSIONS_ALLOWED
 /* pk_gcc_immediate */		"GCC",
 /* pk_gcc_next_token */		"GCC",
+/* pk_gcc_next_statement */	"GCC",
 #if GNU_VECTOR_TYPES_ALLOWED && BUILTIN_FUNCTIONS_ENABLED
 /* pk_gnu_riscv */		"riscv",
 /* pk_clang_riscv */		"clang",

src/lower_c99.c

@@ -4483,10 +4483,15 @@ Do C99 lowering on an stmk_for statement.
     } else {
       /* The C99 case: move the initialization code out into a
          block surrounding the for loop.  Note that this is particularly
-         desirable when there is a VLA declaration in the initialization. */
+         desirable when there is a VLA declaration in the initialization.
+         Any pragmas attached to the for loop (e.g., "#pragma GCC unroll")
+         must stay with the for loop. */
       an_insert_location insert_location;
       flp->initialization = NULL;
-      turn_statement_into_block(for_stmt, &insert_location, &for_stmt);
+      turn_statement_into_block_transferring_pragma(for_stmt,
+                                                    &insert_location,
+                                                    &for_stmt,
+                                                    curr_context->scope);
       reinsert_for_loop_initialization(init_stmt, &insert_location);
     }  /* if */
   }  /* if */

src/lower_il.c

@@ -18407,7 +18407,7 @@ the try-block has been rewritten).
 }  /* put_block_around_try_block */
 
 
-static void turn_statement_into_block_transferring_pragma(
+void turn_statement_into_block_transferring_pragma(
                                         a_statement_ptr        statement,
                                         an_insert_location_ptr insert_location,
                                         a_statement_ptr        *orig_statement,
@@ -19763,9 +19763,12 @@ If the "for" statement has an associated "break" label, lower it also.
       break_label_stmt->next = NULL;
     }  /* if */
     /* Put a block statement around the for-loop and attach the scope
-       to that block. */
+       to that block.  Any pragmas attached to the for-loop (e.g., a
+       "#pragma GCC unroll") stay with the for-loop. */
     block_stmt = for_stmt;
-    turn_statement_into_block(for_stmt, &insert_location, &for_stmt);
+    turn_statement_into_block_transferring_pragma(for_stmt, &insert_location,
+                                                  &for_stmt,
+                                                  curr_context->scope);
     if (break_label_stmt != NULL) {
       /* Re-attach the break label after the "for" statement entry. */
       check_assertion(for_stmt->next == NULL);
@@ -19795,7 +19798,10 @@ If the "for" statement has an associated "break" label, lower it also.
       /* Put a block around the for loop if we didn't previously. */
       if (block_stmt == NULL) {
         block_stmt = for_stmt;
-        turn_statement_into_block(for_stmt, &insert_location, &for_stmt);
+        turn_statement_into_block_transferring_pragma(for_stmt,
+                                                      &insert_location,
+                                                      &for_stmt,
+                                                      curr_context->scope);
       }  /* if */
       reinsert_for_loop_initialization(init_stmt, &insert_location);
     }  /* if */
@@ -19895,11 +19901,14 @@ the following lowered C code is generated:
   push_context(&range_based_for_context, range_based_for_scope,
                (an_object_lifetime_ptr)NULL);
   /* Put a block statement around the range-based-for and attach the
-     range_based_for scope to that block.  Note that any pragmas attached to
-     the range-based-for statement will now be associated with the block. */
+     range_based_for scope to that block.  Any pragmas attached to the
+     range-based-for statement (e.g., a "#pragma GCC unroll") stay with the
+     statement, which becomes the lowered "for" loop. */
   outer_block = range_based_for_stmt;
-  turn_statement_into_block(range_based_for_stmt, &outer_insert_location,
-                            &range_based_for_stmt);
+  turn_statement_into_block_transferring_pragma(range_based_for_stmt,
+                                                &outer_insert_location,
+                                                &range_based_for_stmt,
+                                                curr_context->scope);
   outer_block->variant.block.extra_info->assoc_scope = range_based_for_scope;
   range_based_for_scope->assoc_block = outer_block;
   if (range_based_for_scope->lifetime != NULL) {

src/lower_il.h

@@ -1200,6 +1200,12 @@ extern void turn_statement_into_block(a_statement_ptr        statement,
                                       an_insert_location_ptr insert_location,
                                       a_statement_ptr        *orig_statement);
 
+extern void turn_statement_into_block_transferring_pragma(
+                                        a_statement_ptr        statement,
+                                        an_insert_location_ptr insert_location,
+                                        a_statement_ptr        *orig_statement,
+                                        a_scope_ptr            scope);
+
 extern void put_block_around_try_block(a_statement_ptr        statement,
                                        an_insert_location_ptr insert_location,
                                        a_statement_ptr        *orig_statement);

src/pragma.c

@@ -351,6 +351,7 @@ Construct a pending pragma with the given pragma kind description.
 #if GNU_EXTENSIONS_ALLOWED
     case pk_gcc_immediate:
     case pk_gcc_next_token:
+    case pk_gcc_next_statement:
       clear_gcc_pragma_descr(&this->variant.gcc);
       break;
 #if GNU_VECTOR_TYPES_ALLOWED && BUILTIN_FUNCTIONS_ENABLED
@@ -1857,11 +1858,28 @@ Initialize the pragma description table.
 #endif /* SUN_EXTENSIONS_ALLOWED */
 #if GNU_EXTENSIONS_ALLOWED
   if (gnu_mode && gnu_version >= 40200) {
-    /* "GCC" pragmas are handled by pk_gcc_next_token or pk_gcc_immediate
-       depending on the specific variety of "GCC" pragma.  Currently
-       "GCC diagnostic" pragmas are pk_gcc_next_token and all others are
-       pk_gcc_immediate.  Note that the order of these next two calls is
+    /* "GCC" pragmas are handled by pk_gcc_next_statement, pk_gcc_next_token,
+       or pk_gcc_immediate depending on the specific variety of "GCC" pragma.
+       Currently "GCC unroll", "GCC ivdep", and "GCC novector" pragmas
+       (which apply to the loop that follows them) are pk_gcc_next_statement,
+       "GCC diagnostic" pragmas are pk_gcc_next_token, and all others are
+       pk_gcc_immediate.  Note that the order of these next three calls is
        important (look_up_pragma_id relies on it). */
+    (void)add_next_construct_pragma_kind_description
+                 ((a_pragma_kind)pk_gcc_next_statement,
+                 (a_function_number)fn_null,
+                 /*is_pseudo_pragma=*/FALSE,
+                 /*may_bind_to_decl=*/FALSE,
+                 /*may_bind_to_stmt=*/TRUE,
+                 /*automatically_include_in_il=*/TRUE,
+                 /*record_pragma_text=*/TRUE,
+                 /*expand_macros=*/FALSE,
+                 /*processing_C_code=*/TRUE,
+                 /*fetch_pp_tokens=*/FALSE,
+                 /*ignore_in_back_end=*/FALSE,
+                 /*il_info_is_complete=*/TRUE,
+                 /*read_string_as_header_name=*/FALSE,
+                 es_warning);
     (void)add_next_token_pragma_kind_description
                  ((a_pragma_kind)pk_gcc_next_token,
                  fn_for_function(gcc_pragma),

src/preproc.c

@@ -3262,6 +3262,31 @@ only, only preprocessing immediate pragmas are actually processed.
   }  /* if */
 }  /* record_pragma */
 
+#if GNU_EXTENSIONS_ALLOWED
+
+static a_boolean is_gcc_loop_pragma_name(a_const_char *ptr)
+/*
+Return TRUE if the characters at ptr are the name of one of the "GCC" pragmas
+that must immediately precede, and apply to a loop statement.
+Currently supported: "unroll", "ivdep", and "novector".
+*/
+{
+  static a_const_char *const loop_pragma_names[] = {
+    "unroll", "ivdep", "novector"
+  };
+  a_boolean is_loop_pragma = FALSE;
+
+  for (a_const_char *name : loop_pragma_names) {
+    size_t len = strlen(name);
+    if (strncmp(ptr, name, len) == 0 && !is_id_char[ptr[len]-CHAR_MIN]) {
+      is_loop_pragma = TRUE;
+      break;
+    }  /* if */
+  }  /* for */
+  return is_loop_pragma;
+}  /* is_gcc_loop_pragma_name */
+
+#endif /* GNU_EXTENSIONS_ALLOWED */
 
 a_pragma_kind_description_ptr look_up_pragma_id(
 					a_source_position	*id_position)
@@ -3297,8 +3322,8 @@ The position of the pragma ID is returned in id_position;
       if (curr_id_matches_pragma_id(pkdp->kind)) {
 #if GNU_EXTENSIONS_ALLOWED
         /* We found a match.  If we're processing a GCC pragma, see if we
-           should treat it as an immediate pragma or a next_token pragma
-           based on the token that follows "GCC". */
+           should treat it as an immediate pragma, a next_token pragma, or
+           a next_statement pragma based on the token that follows "GCC". */
         if (pkdp->kind == (a_pragma_kind)pk_gcc_immediate) {
           /* We want to look ahead to see if "diagnostic" is next, but
              being that we're in a preprocessing directive, next_token
@@ -3311,6 +3336,10 @@ The position of the pragma ID is returned in id_position;
             /* Treat all "GCC diagnostic" pragmas as next_token. */
             pkdp = pkdp->next;
             check_assertion(pkdp->kind == (a_pragma_kind)pk_gcc_next_token);
+          } else if (is_gcc_loop_pragma_name(curr_char_loc)) {
+            /* Bind the GCC loop pragmas to the statement that follows. */
+            pkdp = pragma_description_for_pragma_kind[
+                                                   (int)pk_gcc_next_statement];
           }  /* if */
 #if GNU_VECTOR_TYPES_ALLOWED && BUILTIN_FUNCTIONS_ENABLED
         } else if (pkdp->kind == pk_clang_riscv) {

tests/expectations/edg_x86_64/imported.log

@@ -4161,7 +4161,6 @@ gnu/c/torture/no-callee-saved-run-1a.sft.c:rp:-DTEST_NUMBER=1:FAIL(COMPILE):
 gnu/c/torture/pr100329.sft.c:s:-DTEST_NUMBER=1 -w:SKIPPED:
 gnu/c/torture/pr100519.sft.c:s:-DTEST_NUMBER=1 -w:SKIPPED:
 gnu/c/torture/pr100778.sft.c:rp:-DTEST_NUMBER=1:FAIL(COMPILE):
-gnu/c/torture/pr101173.sft.c:rp:-DTEST_NUMBER=1:BADC(COMPILE):
 gnu/c/torture/pr101512.sft.c:fp:-DTEST_NUMBER=1 -w:FAIL:
 gnu/c/torture/pr103181.sft.c:rp:-DTEST_NUMBER=1:FAIL(COMPILE):
 gnu/c/torture/pr103596.sft.c:s:-DTEST_NUMBER=1:SKIPPED:
@@ -4225,7 +4224,6 @@ gnu/c/torture/pr77646.sft.c:fp:-DTEST_NUMBER=1:FAIL:
 gnu/c/torture/pr79536.sft.c:fp:-DTEST_NUMBER=1:FAIL:
 gnu/c/torture/pr79908.sft.c:fp:-DTEST_NUMBER=1:FAIL:
 gnu/c/torture/pr79970.sft.c:fn:-DTEST_NUMBER=1:FAIL:
-gnu/c/torture/pr80304.sft.c:rp:-DTEST_NUMBER=1:BADC(COMPILE):
 gnu/c/torture/pr80612.sft.c:fp:-DTEST_NUMBER=1:FAIL:
 gnu/c/torture/pr80764.sft.c:fp:-DTEST_NUMBER=1:FAIL:
 gnu/c/torture/pr8081.sft.c:rp:-DTEST_NUMBER=1:FAIL(COMPILE):
@@ -7410,7 +7408,6 @@ gnu/cpp/ext/pr84724-1.sft.cpp:fp:-DTEST_NUMBER=1:FAIL:
 gnu/cpp/ext/pr84724-2.sft.cpp:fp:-DTEST_NUMBER=1 -w:FAIL:
 gnu/cpp/ext/pr84828.sft.cpp:fn:-DTEST_NUMBER=1:FAIL:
 gnu/cpp/ext/pr85503.sft.cpp:fp:-DTEST_NUMBER=1 --c++11:FAIL:
-gnu/cpp/ext/pragma-unroll-lambda-lto.sft.cpp:lp:-DTEST_NUMBER=1 --c++11:BADC:
 gnu/cpp/ext/restrict2.sft.cpp:fp:-DTEST_NUMBER=1:FAIL:
 gnu/cpp/ext/selectany1.sft.cpp:fp:-DTEST_NUMBER=1:FAIL:
 gnu/cpp/ext/spe1.sft.cpp:fp:-DTEST_NUMBER=1:FAIL:
@@ -8973,7 +8970,6 @@ gnu/cpp/torture/darwin-cfstring-3.sft.cpp:fp:-DTEST_NUMBER=1:CATASTROPHE:
 gnu/cpp/torture/phi-1.sft.cpp:s:-DTEST_NUMBER=1 --c++11:SKIPPED:
 gnu/cpp/torture/pr101373.sft.cpp:rp:-DTEST_NUMBER=1:FAIL:
 gnu/cpp/torture/pr103669.sft.cpp:s:-DTEST_NUMBER=1:SKIPPED:
-gnu/cpp/torture/pr104601.sft.cpp:rp:-DTEST_NUMBER=1 --c++17:BADC(COMPILE):
 gnu/cpp/torture/pr109262.sft.cpp:fp:-DTEST_NUMBER=1:FAIL:
 gnu/cpp/torture/pr111465.sft.cpp:s:-DTEST_NUMBER=1 --no_exceptions:SKIPPED:
 gnu/cpp/torture/pr115694.sft.cpp:fp:-DTEST_NUMBER=1:FAIL:
@@ -8995,7 +8991,6 @@ gnu/cpp/torture/pr64312.sft.cpp:fn:-DTEST_NUMBER=1:FAIL:
 gnu/cpp/torture/pr69355.sft.cpp:rp:-DTEST_NUMBER=1:FAIL(COMPILE):
 gnu/cpp/torture/pr77919-2.sft.cpp:fp:-DTEST_NUMBER=1:FAIL:
 gnu/cpp/torture/pr79905.sft.cpp:fp:-DTEST_NUMBER=1:FAIL:
-gnu/cpp/torture/pr81877.sft.cpp:rp:-DTEST_NUMBER=1:BADC(COMPILE):
 gnu/cpp/torture/pr82985.sft.cpp:fp:-DTEST_NUMBER=1 -w:FAIL:
 gnu/cpp/torture/pr84961-1.sft.cpp:fp:-DTEST_NUMBER=1:FAIL:
 gnu/cpp/torture/pr85013.sft.cpp:s:-DTEST_NUMBER=1 --c++14:SKIPPED: