On Mon, Aug 04, 2014 at 02:04:36PM +0200, Richard Biener wrote:
> > Looks like .fre can optimize "q - (q - 1)" into 1:
> > <bb 2>:
> > q.0_3 = (long int) &MEM[(void *)&i + 4B];
> > _5 = (long int) &i;
> > - _6 = q.0_3 - _5;
> > - t.1_7 = _6 /[ex] 4;
> > - t ={v} t.1_7;
> > + t ={v} 1;
> > i ={v} {CLOBBER};
> > return;
> >
> > But associate_plusminus doesn't optimize it:
> > else if (code == MINUS_EXPR
> > && CONVERT_EXPR_CODE_P (def_code)
> > && TREE_CODE (gimple_assign_rhs1 (def_stmt)) == SSA_NAME
> > && TREE_CODE (rhs2) == SSA_NAME)
> > {
> > /* (T)(P + A) - (T)P -> (T)A. */
> > becase gimple_assign_rhs1 (def_stmt) is not an SSA_NAME, but ADDR_EXPR (it's
> > &MEM[(void *)&i + 4B]). Then there's transformation A - (A +- B) -> -+ B
> > below, but that doesn't handle casts.
> >
> > So - should I try to handle it in associate_plusminus?
>
> Yes please, with a (few) testcase(s).
Ok, so the following adds the (T)P - (T)(P + A) -> (T)-A
transformation. It is based on code hunk that does the
(T)(P + A) - (T)P -> (T)A transformation. The difference it makes is
in the .optimized dump something like:
int fn2(int, int) (int p, int i)
{
- unsigned int p.2_2;
+ unsigned int _3;
int _4;
- unsigned int _5;
unsigned int _6;
- int _7;
<bb 2>:
- p.2_2 = (unsigned int) p_1(D);
- _4 = p_1(D) + i_3(D);
- _5 = (unsigned int) _4;
- _6 = p.2_2 - _5;
- _7 = (int) _6;
- return _7;
+ _6 = (unsigned int) i_2(D);
+ _3 = -_6;
+ _4 = (int) _3;
+ return _4;
i.e., the PLUS_EXPR and MINUS_EXPR are gone, and NEGATE_EXPR is used instead.
During bootstrap with --enable-languages=c,c++ this optimization triggered 238
times.
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2014-08-05 Marek Polacek <pola...@redhat.com>
PR c/61240
* tree-ssa-forwprop.c (associate_plusminus): Add (T)P - (T)(P + A)
-> (T)-A transformation.
c/
* c-typeck.c (pointer_diff): Remove P - (P + CST) optimization.
testsuite/
* gcc.dg/pr61240.c: New test.
* gcc.dg/tree-ssa/forwprop-29.c: New test.
diff --git gcc/c/c-typeck.c gcc/c/c-typeck.c
index fe9440c..5f46944 100644
--- gcc/c/c-typeck.c
+++ gcc/c/c-typeck.c
@@ -3460,7 +3460,6 @@ pointer_diff (location_t loc, tree op0, tree op1)
addr_space_t as0 = TYPE_ADDR_SPACE (TREE_TYPE (TREE_TYPE (op0)));
addr_space_t as1 = TYPE_ADDR_SPACE (TREE_TYPE (TREE_TYPE (op1)));
tree target_type = TREE_TYPE (TREE_TYPE (op0));
- tree con0, con1, lit0, lit1;
tree orig_op1 = op1;
/* If the operands point into different address spaces, we need to
@@ -3490,7 +3489,6 @@ pointer_diff (location_t loc, tree op0, tree op1)
else
inttype = restype;
-
if (TREE_CODE (target_type) == VOID_TYPE)
pedwarn (loc, OPT_Wpointer_arith,
"pointer of type %<void *%> used in subtraction");
@@ -3498,50 +3496,6 @@ pointer_diff (location_t loc, tree op0, tree op1)
pedwarn (loc, OPT_Wpointer_arith,
"pointer to a function used in subtraction");
- /* If the conversion to ptrdiff_type does anything like widening or
- converting a partial to an integral mode, we get a convert_expression
- that is in the way to do any simplifications.
- (fold-const.c doesn't know that the extra bits won't be needed.
- split_tree uses STRIP_SIGN_NOPS, which leaves conversions to a
- different mode in place.)
- So first try to find a common term here 'by hand'; we want to cover
- at least the cases that occur in legal static initializers. */
- if (CONVERT_EXPR_P (op0)
- && (TYPE_PRECISION (TREE_TYPE (op0))
- == TYPE_PRECISION (TREE_TYPE (TREE_OPERAND (op0, 0)))))
- con0 = TREE_OPERAND (op0, 0);
- else
- con0 = op0;
- if (CONVERT_EXPR_P (op1)
- && (TYPE_PRECISION (TREE_TYPE (op1))
- == TYPE_PRECISION (TREE_TYPE (TREE_OPERAND (op1, 0)))))
- con1 = TREE_OPERAND (op1, 0);
- else
- con1 = op1;
-
- if (TREE_CODE (con0) == POINTER_PLUS_EXPR)
- {
- lit0 = TREE_OPERAND (con0, 1);
- con0 = TREE_OPERAND (con0, 0);
- }
- else
- lit0 = integer_zero_node;
-
- if (TREE_CODE (con1) == POINTER_PLUS_EXPR)
- {
- lit1 = TREE_OPERAND (con1, 1);
- con1 = TREE_OPERAND (con1, 0);
- }
- else
- lit1 = integer_zero_node;
-
- if (operand_equal_p (con0, con1, 0))
- {
- op0 = lit0;
- op1 = lit1;
- }
-
-
/* First do the subtraction as integers;
then drop through to build the divide operator.
Do not do default conversions on the minus operator
diff --git gcc/testsuite/gcc.dg/pr61240.c gcc/testsuite/gcc.dg/pr61240.c
index e69de29..115e415 100644
--- gcc/testsuite/gcc.dg/pr61240.c
+++ gcc/testsuite/gcc.dg/pr61240.c
@@ -0,0 +1,13 @@
+/* PR c/61240 */
+/* { dg-do compile } */
+
+void
+foo (void)
+{
+ volatile __PTRDIFF_TYPE__ t;
+ int i;
+ int *p = &i;
+ int *q = &i + 1;
+ t = q - (q - 1);
+ t = p - (p - 1);
+}
diff --git gcc/testsuite/gcc.dg/tree-ssa/forwprop-29.c
gcc/testsuite/gcc.dg/tree-ssa/forwprop-29.c
index e69de29..745a494 100644
--- gcc/testsuite/gcc.dg/tree-ssa/forwprop-29.c
+++ gcc/testsuite/gcc.dg/tree-ssa/forwprop-29.c
@@ -0,0 +1,85 @@
+/* { dg-do run } */
+/* { dg-options "-O -fdump-tree-forwprop1" } */
+
+__PTRDIFF_TYPE__ __attribute__((noinline, noclone))
+fn1 (int *p, long int i)
+{
+ return p - (p + i);
+}
+
+int __attribute__((noinline, noclone))
+fn2 (int p, int i)
+{
+ return (long) p - (p + i);
+}
+
+long int __attribute__((noinline, noclone))
+fn3 (long int c, long int i)
+{
+ return (unsigned long) c - (c + i);
+}
+
+int
+main ()
+{
+ int l = 10;
+ if (fn1 (&l, 1) != -1
+ || fn1 (&l, -1) != 1
+ || fn1 (&l, 0) != 0
+ || fn1 (&l, 0x186A0) != -0x186A0
+ || fn1 (&l, 0xb3c2) != -0xb3c2
+ || fn1 (&l, 0xb3) != -0xb3
+ || fn1 (&l, 0xacf) != -0xacf
+ || fn1 (&l, 0xf) != -0xf
+ || fn1 (&l, 0x2468acf) != -0x2468acf
+ || fn1 (&l, 0x91a2b3c) != -0x91a2b3c
+ || fn1 (&l, -0x186A0) != 0x186A0
+ || fn1 (&l, -0xb3c2) != 0xb3c2
+ || fn1 (&l, -0xb3) != 0xb3
+ || fn1 (&l, -0xacf) != 0xacf
+ || fn1 (&l, -0xf) != 0xf
+ || fn1 (&l, -0x2468acf) != 0x2468acf
+ || fn1 (&l, -0x91a2b3c) != 0x91a2b3c)
+ __builtin_abort ();
+ if (fn2 (l, 1) != -1
+ || fn2 (l, -1) != 1
+ || fn2 (l, 0) != 0
+ || fn2 (l, 0x186A0) != -0x186A0
+ || fn2 (l, 0xb3c2) != -0xb3c2
+ || fn2 (l, 0xb3) != -0xb3
+ || fn2 (l, 0xacf) != -0xacf
+ || fn2 (l, 0xf) != -0xf
+ || fn2 (l, 0x2468acf) != -0x2468acf
+ || fn2 (l, 0x91a2b3c) != -0x91a2b3c
+ || fn2 (l, -0x186A0) != 0x186A0
+ || fn2 (l, -0xb3c2) != 0xb3c2
+ || fn2 (l, -0xb3) != 0xb3
+ || fn2 (l, -0xacf) != 0xacf
+ || fn2 (l, -0xf) != 0xf
+ || fn2 (l, -0x2468acf) != 0x2468acf
+ || fn2 (l, -0x91a2b3c) != 0x91a2b3c)
+ __builtin_abort ();
+ if (fn3 (l, 1) != -1
+ || fn3 (l, -1) != 1
+ || fn3 (l, 0) != 0
+ || fn3 (l, 0x186A0) != -0x186A0
+ || fn3 (l, 0xb3c2) != -0xb3c2
+ || fn3 (l, 0xb3) != -0xb3
+ || fn3 (l, 0xacf) != -0xacf
+ || fn3 (l, 0xf) != -0xf
+ || fn3 (l, 0x2468acf) != -0x2468acf
+ || fn3 (l, 0x91a2b3c) != -0x91a2b3c
+ || fn3 (l, -0x186A0) != 0x186A0
+ || fn3 (l, -0xb3c2) != 0xb3c2
+ || fn3 (l, -0xb3) != 0xb3
+ || fn3 (l, -0xacf) != 0xacf
+ || fn3 (l, -0xf) != 0xf
+ || fn3 (l, -0x2468acf) != 0x2468acf
+ || fn3 (l, -0x91a2b3c) != 0x91a2b3c)
+ __builtin_abort ();
+
+ return 0;
+}
+
+/* { dg-final { scan-tree-dump-not " - " "forwprop1" } } */
+/* { dg-final { cleanup-tree-dump "forwprop1" } } */
diff --git gcc/tree-ssa-forwprop.c gcc/tree-ssa-forwprop.c
index 0284301..c59f1d7 100644
--- gcc/tree-ssa-forwprop.c
+++ gcc/tree-ssa-forwprop.c
@@ -2534,13 +2534,14 @@ associate_plusminus (gimple_stmt_iterator *gsi)
(CST +- A) +- CST -> CST +- A
(A +- CST) +- CST -> A +- CST
~A + A -> -1
- ~A + 1 -> -A
+ ~A + 1 -> -A
A - (A +- B) -> -+ B
A +- (B +- A) -> +- B
CST +- (CST +- A) -> CST +- A
CST +- (A +- CST) -> CST +- A
A + ~A -> -1
(T)(P + A) - (T)P -> (T)A
+ (T)P - (T)(P + A) -> (T)-A
via commutating the addition and contracting operations to zero
by reassociation. */
@@ -2799,6 +2800,76 @@ associate_plusminus (gimple_stmt_iterator *gsi)
gimple_set_modified (stmt, true);
}
}
+ else if (code == MINUS_EXPR
+ && CONVERT_EXPR_CODE_P (def_code)
+ && TREE_CODE (gimple_assign_rhs1 (def_stmt)) == SSA_NAME
+ && TREE_CODE (rhs1) == SSA_NAME)
+ {
+ /* (T)P - (T)(P + A) -> (T)-A. */
+ gimple def_stmt2 = SSA_NAME_DEF_STMT (rhs1);
+ if (is_gimple_assign (def_stmt2)
+ && can_propagate_from (def_stmt2)
+ && CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (def_stmt2))
+ && TREE_CODE (gimple_assign_rhs1 (def_stmt2)) == SSA_NAME)
+ {
+ /* Now we have (T)P - (T)X. */
+ tree p = gimple_assign_rhs1 (def_stmt2);
+ def_stmt2 = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (def_stmt));
+ if (is_gimple_assign (def_stmt2)
+ && can_propagate_from (def_stmt2)
+ && (gimple_assign_rhs_code (def_stmt2) ==
POINTER_PLUS_EXPR
+ || gimple_assign_rhs_code (def_stmt2) == PLUS_EXPR)
+ && gimple_assign_rhs1 (def_stmt2) == p)
+ {
+ /* And finally (T)P - (T)(P + A). */
+ tree a = gimple_assign_rhs2 (def_stmt2);
+ if (TYPE_PRECISION (TREE_TYPE (rhs1))
+ <= TYPE_PRECISION (TREE_TYPE (a))
+ /* For integer types, if A has a smaller type
+ than T the result depends on the possible
+ overflow in P + A.
+ E.g. T=size_t, A=(unsigned)429497295, P>0.
+ However, if an overflow in P + A would cause
+ undefined behavior, we can assume that there
+ is no overflow. */
+ || (INTEGRAL_TYPE_P (TREE_TYPE (p))
+ && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (p)))
+ /* For pointer types, if the conversion of A to the
+ final type requires a sign- or zero-extension,
+ then we have to punt - it is not defined which
+ one is correct. */
+ || (POINTER_TYPE_P (TREE_TYPE (p))
+ && TREE_CODE (a) == INTEGER_CST
+ && tree_int_cst_sign_bit (a) == 0))
+ {
+ if (issue_strict_overflow_warning
+ (WARN_STRICT_OVERFLOW_MISC)
+ && TYPE_PRECISION (TREE_TYPE (rhs1))
+ > TYPE_PRECISION (TREE_TYPE (a))
+ && INTEGRAL_TYPE_P (TREE_TYPE (p)))
+ warning_at (gimple_location (stmt),
+ OPT_Wstrict_overflow,
+ "assuming signed overflow does not "
+ "occur when assuming that "
+ "(T)P - (T)(P + A) is always (T)-A");
+ if (!useless_type_conversion_p (TREE_TYPE (rhs1),
+ TREE_TYPE (a)))
+ {
+ a = fold_convert (TREE_TYPE (rhs1), a);
+ a = force_gimple_operand_gsi (gsi, a, true,
+ NULL_TREE, true,
+ GSI_SAME_STMT);
+ }
+ rhs1 = a;
+ rhs2 = NULL_TREE;
+ gimple_assign_set_rhs_with_ops (gsi, NEGATE_EXPR,
+ rhs1, rhs2);
+ gcc_assert (gsi_stmt (*gsi) == stmt);
+ gimple_set_modified (stmt, true);
+ }
+ }
+ }
+ }
}
}
Marek
