[Bug middle-end/61893] New: Constant folding inhibits trapping with -ftrapv

[Bug middle-end/61893] New: Constant folding inhibits trapping with -ftrapv

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61893

            Bug ID: 61893
           Summary: Constant folding inhibits trapping with -ftrapv
           Product: gcc
           Version: 4.9.1
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org

int
iaddv (void)
{
  return __INT_MAX__ + 1;
}

> ./cc1 -quiet t2.c -ftrapv
t2.c: In function 'iaddv':
t2.c:4:24: warning: integer overflow in expression [-Woverflow]
     return __INT_MAX__ + 1;
                        ^

iaddv:
.LFB0:
        .cfi_startproc
        pushq   %rbp
        .cfi_def_cfa_offset 16
        .cfi_offset 6, -16
        movq    %rsp, %rbp
        .cfi_def_cfa_register 6
        movl    $-2147483648, %eax
        popq    %rbp
        .cfi_def_cfa 7, 8
        ret

[Bug middle-end/61893] Constant folding inhibits trapping with -ftrapv

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61893

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed by sth like

Index: fold-const.c
===================================================================
--- fold-const.c        (revision 212388)
+++ fold-const.c        (working copy)
@@ -1121,7 +1121,12 @@
   STRIP_NOPS (arg2);

   if (TREE_CODE (arg1) == INTEGER_CST)
-    return int_const_binop (code, arg1, arg2);
+    {
+      tree res = int_const_binop (code, arg1, arg2);
+      if (res && TYPE_OVERFLOW_TRAPS (TREE_TYPE (arg1)) && TREE_OVERFLOW
(res))
+        return NULL_TREE;
+      return res;
+    }

   if (TREE_CODE (arg1) == REAL_CST)
     {

[Bug middle-end/61893] Constant folding inhibits trapping with -ftrapv

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61893

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixing bit-ccp with

Index: tree-ssa-ccp.c
===================================================================
--- tree-ssa-ccp.c      (revision 213040)
+++ tree-ssa-ccp.c      (working copy)
@@ -1456,8 +1456,19 @@ bit_value_unop (enum tree_code code, tre
   widest_int value, mask;
   prop_value_t val;

-  if (rval.lattice_val == UNDEFINED)
-    return rval;
+  if (rval.lattice_val == UNDEFINED
+      /* If the value is fully known constants assume that
+        earlier simplification failed for a reason, for example
+        due to -ftrapv.  */
+      || (rval.lattice_val == CONSTANT
+         && TREE_CODE (rval.value) == INTEGER_CST
+         && rval.mask == -1))
+    {
+      val.lattice_val = VARYING;
+      val.value = NULL_TREE;
+      val.mask = -1;
+      return val;
+    }

   gcc_assert ((rval.lattice_val == CONSTANT
               && TREE_CODE (rval.value) == INTEGER_CST)
@@ -1492,7 +1503,16 @@ bit_value_binop (enum tree_code code, tr
   prop_value_t val;

   if (r1val.lattice_val == UNDEFINED
-      || r2val.lattice_val == UNDEFINED)
+      || r2val.lattice_val == UNDEFINED
+      /* If both values are fully known constants assume that
+        earlier simplification failed for a reason, for example
+        due to -ftrapv.  */
+      || (r1val.lattice_val == CONSTANT
+         && TREE_CODE (r1val.value) == INTEGER_CST
+         && r1val.mask == 0
+         && r2val.lattice_val == CONSTANT
+         && TREE_CODE (r2val.value) == INTEGER_CST
+         && r2val.mask == 0))
     {
       val.lattice_val = VARYING;
       val.value = NULL_TREE;

reveals that expansion produces

(insn 5 4 6 (set (reg:SI 4 si)
        (const_int 1 [0x1])) t.c:7 -1
     (nil))

(insn 6 5 7 (set (reg:SI 5 di)
        (const_int 2147483647 [0x7fffffff])) t.c:7 -1
     (nil))

(call_insn/u 7 6 8 (set (reg:SI 0 ax)
        (call (mem:QI (symbol_ref:DI ("__addvsi3") [flags 0x41]) [0  S1 A8])
            (const_int 0 [0]))) t.c:7 -1
     (expr_list:REG_EH_REGION (const_int -2147483648 [0xffffffff80000000])
        (nil))
    (expr_list (use (reg:SI 4 si))
        (expr_list (use (reg:SI 5 di))
            (nil))))

(insn 8 7 9 (set (reg:SI 86 [ D.1753 ])
        (reg:SI 0 ax)) t.c:7 -1
     (expr_list:REG_EQUAL (plus:SI (const_int 2147483647 [0x7fffffff])
            (const_int 1 [0x1]))
        (nil)))

note the REG_EQUAL note which CSE happily simplifies and substitutes...

Index: optabs.c
===================================================================
--- optabs.c    (revision 213040)
+++ optabs.c    (working copy)
@@ -3985,7 +3985,8 @@ emit_libcall_block_1 (rtx insns, rtx tar
     }

   last = emit_move_insn (target, result);
-  set_dst_reg_note (last, REG_EQUAL, copy_rtx (equiv), target);
+  if (!equiv_may_trap)
+    set_dst_reg_note (last, REG_EQUAL, copy_rtx (equiv), target);

   if (final_dest != target)
     emit_move_insn (final_dest, target);


with that we finally trap with -O2...

[Bug middle-end/61893] Constant folding inhibits trapping with -ftrapv

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61893

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2014-08-27
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
     Ever confirmed|0                           |1

[Bug middle-end/61893] Constant folding inhibits trapping with -ftrapv

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61893

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |eggert at gnu dot org

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
*** Bug 68046 has been marked as a duplicate of this bug. ***

[Bug middle-end/61893] Constant folding inhibits trapping with -ftrapv

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61893

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Author: rguenth
Date: Thu Oct 22 11:44:11 2015
New Revision: 229170

URL: https://gcc.gnu.org/viewcvs?rev=229170&root=gcc&view=rev
Log:
2015-10-22  Richard Biener  <rguenther@suse.de>

        PR middle-end/68046
        PR middle-end/61893
        * optabs.c (emit_libcall_block_1): Allow a NULL_RTX equiv.
        (expand_binop): For -ftrapv optabs do not record an REG_EQUAL note.
        (expand_unop): Likewise.

        * gcc.dg/torture/ftrapv-2.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.dg/torture/ftrapv-2.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/optabs.c
    trunk/gcc/testsuite/ChangeLog

[Bug middle-end/61893] Constant folding inhibits trapping with -ftrapv

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61893

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note only the non-constant-folding part is fixed (the REG_EQUAL notes which
enable combine to remove the trapping).

[Bug middle-end/61893] Constant folding inhibits trapping with -ftrapv

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61893

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |john at mcfarlane dot name

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 102303 has been marked as a duplicate of this bug. ***