[M3devel] unnecessary temporaries

[Jay K]

parse.c seems to go crazy sometimes on the temporaries.

Here, in min, max, and check_eq:

Index: parse.c
===================================================================
RCS file: /usr/cvs/cm3/m3-sys/m3cc/gcc/gcc/m3cg/parse.c,v
retrieving revision 1.314
diff -u -r1.314 parse.c
--- parse.c    13 Sep 2010 09:59:25 -0000    1.314
+++ parse.c    13 Sep 2010 10:24:16 -0000
@@ -4791,11 +4791,8 @@
 {
   MTYPE (t);
 
-  tree t1 = declare_temp (t);
-  tree t2 = declare_temp (t);
-
-  add_stmt (m3_build2 (MODIFY_EXPR, t, t1, EXPR_REF (-1)));
-  add_stmt (m3_build2 (MODIFY_EXPR, t, t2, EXPR_REF (-2)));
+  tree t1 = stabilize_reference (m3_cast (t, EXPR_REF (-1)));
+  tree t2 = stabilize_reference (m3_cast (t, EXPR_REF (-2)));
 
   EXPR_REF (-2) = m3_build3 (COND_EXPR, t,
                              m3_build2 (LE_EXPR, boolean_type_node, t2, t1),
@@ -4808,11 +4805,8 @@
 {
   MTYPE (t);
 
-  tree t1 = declare_temp (t);
-  tree t2 = declare_temp (t);
-
-  add_stmt (m3_build2 (MODIFY_EXPR, t, t1, EXPR_REF (-1)));
-  add_stmt (m3_build2 (MODIFY_EXPR, t, t2, EXPR_REF (-2)));
+  tree t1 = stabilize_reference (m3_cast (t, EXPR_REF (-1)));
+  tree t2 = stabilize_reference (m3_cast (t, EXPR_REF (-2)));
 
   EXPR_REF (-2) = m3_build3 (COND_EXPR, t,
                              m3_build2 (LE_EXPR, boolean_type_node, t1, t2),
@@ -5679,11 +5673,10 @@
   MTYPE2  (t, T);
   INTEGER (code);
 
-  tree temp1 = declare_temp (t);
-  tree temp2 = declare_temp (t);
-
-  m3_store (temp1, 0, t, T, t, T);
-  m3_store (temp2, 0, t, T, t, T);
+  tree temp1 = stabilize_reference (m3_cast (t, EXPR_REF (-1)));
+  tree temp2 = stabilize_reference (m3_cast (t, EXPR_REF (-2)));
+  EXPR_POP ();
+  EXPR_POP ();
   add_stmt (build3 (COND_EXPR, t_void,
                     m3_build2 (NE_EXPR, boolean_type_node, temp1, temp2),
                     generate_fault (code),


and in the unoptimized

m3core/src/text/TextCat

PROCEDURE MyGetChars (t: T;  VAR a: ARRAY OF CHAR;  start: CARDINAL) =
  VAR u: TEXT;  a_offset, t_offset, u_offset: CARDINAL := 0;
  BEGIN
    u := t.a;
    IF (t_offset + t.a_len > start) THEN
      u_offset := MAX (start - t_offset, 0);
      u.get_chars (SUBARRAY (a, a_offset, NUMBER (a) - a_offset), u_offset);



7 instructions go down to 3, 4 memory operations saved, and 16 bytes of stack are saved (presumably 12, rounded)



--- I386_DARWIN.3/TextCat.ms    2010-09-13 03:18:45.000000000 -0700
+++ I386_DARWIN.4/TextCat.ms    2010-09-13 03:19:40.000000000 -0700
@@ -835,7 +835,7 @@
 LCFI41:
     movl    %esp, %ebp
 LCFI42:
-    subl    $88, %esp
+    subl    $72, %esp
 LCFI43:
     movl    -16(%ebp), %eax
     andl    $0, %eax
@@ -879,18 +879,14 @@
     movl    16(%ebp), %eax
     cmpl    %eax, %edx
     jle    L54
-    movl    $0, -32(%ebp)
     movl    16(%ebp), %edx
     movl    -20(%ebp), %eax
     movl    %edx, %ecx
     subl    %eax, %ecx
     movl    %ecx, %eax
-    movl    %eax, -36(%ebp)
-    movl    -36(%ebp), %edx
-    movl    -32(%ebp), %eax
-    cmpl    %edx, %eax
-    jge    L49
-    movl    %edx, %eax
+    testl    %eax, %eax
+    jns    L49
+    movl    $0, %eax


Reasonable, eh?
Or should I be nervous?


check_eq in particular -- if you get it wrong, such that it is underaggressive, correct programs
will work the same.


I guess I should make sure m3tests is full of failure cases for that.
Ok, in m3front, it looks like all the uses of check_eq are related to runtime assignments
of open arrays, to make sure their sizes match, or such, either for assignment or passing a parameter.


 - Jay