Hi,
one of the transformations performed by associate_plusminus is:
/* Second match patterns that allow contracting a plus-minus pair
irrespective of overflow issues.
[...]
(T)(P + A) - (T)P -> (T)A
but it is actually applied only to POINTER_PLUS_EXPR and pointer types:
/* (T)(ptr + adj) - (T)ptr -> (T)adj. */
It turns out that this pattern arises for size computations of array slices in
Ada, which are done in integer types; for the attached testcase, extending the
transformation to integer types makes it possible to eliminate a call to the
alloca builtin.
Tested on x86_64-suse-linux, OK for the mainline?
2014-05-21 Eric Botcazou <ebotca...@adacore.com>
* tree.h (PLUS_EXPR_CODE_P): New macro.
(PLUS_EXPR_P): Likewise.
(CASE_PLUS): Likewise.
* tree-ssa-forwprop.c (associate_plusminus): Extend (T)(P+A) - (T)P
-> (T)A transformation to integer types.
2014-05-21 Eric Botcazou <ebotca...@adacore.com>
* gnat.dg/opt37.ad[sb]: New test.
--
Eric Botcazoupackage Opt37 is
type T_Bit is range 0 .. 1;
for T_Bit'Size use 1;
type Positive is range 0 .. (2 ** 31) - 1;
type Unsigned32 is mod 2 ** 32;
subtype T_Bit_Count is Positive;
subtype T_Bit_Index is T_Bit_Count range 1 .. T_Bit_Count'Last;
type T_Bit_Array is array (T_Bit_Count range <>) of T_Bit;
pragma Pack (T_Bit_Array);
function Func (Bit_Array : in T_Bit_Array;
Bit_Index : in T_Bit_Index) return Positive;
end Opt37;-- { dg-compile }
-- { dg-options "-O2 -gnato -fdump-tree-optimized" }
package body Opt37 is
function To_Unchecked (Bits : T_Bit_Array) return Unsigned32 is
Value : Unsigned32 := 0;
begin
for I in Bits'Range loop
Value := Value * 2 + Unsigned32 (Bits(I));
end loop;
return Value;
end;
function To_Scalar (Bits : T_Bit_Array) return Positive is
Tmp : Unsigned32;
Value : Positive;
begin
Tmp := To_Unchecked (Bits);
if Tmp in 0 .. Unsigned32 (Positive'last) then
Value := Positive (Tmp);
else
Value := -Positive (Unsigned32'last - Tmp);
if Value > Positive'first then
Value := Value - 1;
else
raise Program_Error;
end if;
end if;
return Value;
end;
function Func (Bit_Array : T_Bit_Array;
Bit_Index : T_Bit_Index) return Positive is
begin
return To_Scalar (Bit_Array (Bit_Index .. Bit_Index + 1));
end;
end Opt37;
-- { dg-final { scan-tree-dump-not "alloca" "optimized" } }
-- { dg-final { cleanup-tree-dump "optimized" } }Index: tree-ssa-forwprop.c
===================================================================
--- tree-ssa-forwprop.c (revision 210676)
+++ tree-ssa-forwprop.c (working copy)
@@ -2642,49 +2642,46 @@ associate_plusminus (gimple_stmt_iterato
gimple_set_modified (stmt, true);
}
}
- else if (CONVERT_EXPR_CODE_P (def_code) && code == MINUS_EXPR
+ 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)(ptr + adj) - (T)ptr -> (T)adj. */
+ /* (T)(P + A) - (T)P -> (T)A. */
gimple def_stmt2 = SSA_NAME_DEF_STMT (rhs2);
- if (TREE_CODE (gimple_assign_rhs1 (def_stmt)) == SSA_NAME
- && is_gimple_assign (def_stmt2)
+ 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)A - (T)ptr. */
- tree ptr = gimple_assign_rhs1 (def_stmt2);
+ /* Now we have (T)X - (T)P. */
+ tree p = gimple_assign_rhs1 (def_stmt2);
def_stmt2 = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (def_stmt));
if (is_gimple_assign (def_stmt2)
- && gimple_assign_rhs_code (def_stmt2) == POINTER_PLUS_EXPR
- && gimple_assign_rhs1 (def_stmt2) == ptr)
+ && can_propagate_from (def_stmt2)
+ && PLUS_EXPR_CODE_P (gimple_assign_rhs_code (def_stmt2))
+ && gimple_assign_rhs1 (def_stmt2) == p)
{
- /* And finally (T)(ptr + X) - (T)ptr. */
- tree adj = gimple_assign_rhs2 (def_stmt2);
- /* If the conversion of the pointer adjustment to the
- final type requires a sign- or zero-extension we
- have to punt - it is not defined which one is
- correct. */
- if (TYPE_PRECISION (TREE_TYPE (rhs1))
- <= TYPE_PRECISION (TREE_TYPE (adj))
- || (TREE_CODE (adj) == INTEGER_CST
- && tree_int_cst_sign_bit (adj) == 0))
+ /* And finally (T)(P + A) - (T)P. */
+ tree a = gimple_assign_rhs2 (def_stmt2);
+ /* 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. */
+ if (!POINTER_TYPE_P (TREE_TYPE (rhs1))
+ || TYPE_PRECISION (TREE_TYPE (rhs1))
+ <= TYPE_PRECISION (TREE_TYPE (a))
+ || (TREE_CODE (a) == INTEGER_CST
+ && tree_int_cst_sign_bit (a) == 0))
{
if (useless_type_conversion_p (TREE_TYPE (rhs1),
- TREE_TYPE (adj)))
- {
- code = TREE_CODE (adj);
- rhs1 = adj;
- }
+ TREE_TYPE (a)))
+ code = TREE_CODE (a);
else
- {
- code = NOP_EXPR;
- rhs1 = adj;
- }
+ code = NOP_EXPR;
+ rhs1 = a;
rhs2 = NULL_TREE;
gimple_assign_set_rhs_with_ops (gsi, code, rhs1,
- NULL_TREE);
+ rhs2);
gcc_assert (gsi_stmt (*gsi) == stmt);
gimple_set_modified (stmt, true);
}
Index: tree.h
===================================================================
--- tree.h (revision 210676)
+++ tree.h (working copy)
@@ -439,6 +439,19 @@ extern void omp_clause_range_check_faile
case NOP_EXPR: \
case CONVERT_EXPR
+/* Tests if CODE is a plus expr (PLUS_EXPR or POINTER_PLUS_EXPR). */
+#define PLUS_EXPR_CODE_P(CODE) \
+ ((CODE) == PLUS_EXPR || (CODE) == POINTER_PLUS_EXPR)
+
+/* Similarly, but accept an expressions instead of a tree code. */
+#define PLUS_EXPR_P(EXP) PLUS_EXPR_CODE_P (TREE_CODE (EXP))
+
+/* Generate case for PLUS_EXPR, POINTER_PLUS_EXPR. */
+
+#define CASE_PLUS \
+ case PLUS_EXPR: \
+ case POINTER_PLUS_EXPR
+
/* Given an expression as a tree, strip any conversion that generates
no instruction. Accepts both tree and const_tree arguments since
we are not modifying the tree itself. */
