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tree-optimization/111000 - restrict invariant motion of shifts

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The following restricts moving variable shifts to when they are
always executed in the loop as we currently do not have an efficient
way to rewrite them to something that is unconditionally
well-defined and value range analysis will otherwise compute
invalid ranges for the shift operand.

	PR tree-optimization/111000
	* stor-layout.h (element_precision): Move ..
	* tree.h (element_precision): .. here.
	* tree-ssa-loop-im.cc (movement_possibility_1): Restrict
	motion of shifts and rotates.

	* gcc.dg/torture/pr111000.c: New testcase.
This commit is contained in:
Richard Biener 2023-10-20 11:54:07 +02:00
parent 551935d118
commit d118738e71
4 changed files with 40 additions and 1 deletions
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1
gcc/stor-layout.h
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@ -36,7 +36,6 @@ extern void place_field (record_layout_info, tree);
extern void compute_record_mode (tree);
extern void finish_bitfield_layout (tree);
extern void finish_record_layout (record_layout_info, int);
extern unsigned int element_precision (const_tree);
extern void finalize_size_functions (void);
extern void fixup_unsigned_type (tree);
extern void initialize_sizetypes (void);

21
gcc/testsuite/gcc.dg/torture/pr111000.c Normal file
View file

@ -0,0 +1,21 @@
/* { dg-do run } */
volatile int a = 68;
int b, d, e;
int main()
{
int t = a;
for (; d <= 6; d++) {
for (b = 0; b <= 6; b++) {
if (t >= 31)
e = d;
else if (d > (647 >> t))
e = d;
else
e = 0;
}
}
if (e != 6)
__builtin_abort();
return 0;
}

18
gcc/tree-ssa-loop-im.cc
View file

@ -400,6 +400,24 @@ movement_possibility_1 (gimple *stmt)
|| gimple_could_trap_p (stmt))
return MOVE_PRESERVE_EXECUTION;
if (is_gimple_assign (stmt))
{
auto code = gimple_assign_rhs_code (stmt);
tree type = TREE_TYPE (gimple_assign_rhs1 (stmt));
/* For shifts and rotates and possibly out-of-bound shift operands
we currently cannot rewrite them into something unconditionally
well-defined. */
if ((code == LSHIFT_EXPR
|| code == RSHIFT_EXPR
|| code == LROTATE_EXPR
|| code == RROTATE_EXPR)
&& (TREE_CODE (gimple_assign_rhs2 (stmt)) != INTEGER_CST
/* We cannot use ranges at 'stmt' here. */
|| wi::ltu_p (wi::to_wide (gimple_assign_rhs2 (stmt)),
element_precision (type))))
ret = MOVE_PRESERVE_EXECUTION;
}
/* Non local loads in a transaction cannot be hoisted out. Well,
unless the load happens on every path out of the loop, but we
don't take this into account yet. */

1
gcc/tree.h
View file

@ -2235,6 +2235,7 @@ class auto_suppress_location_wrappers
#define SET_TYPE_MODE(NODE, MODE) \
(TYPE_CHECK (NODE)->type_common.mode = (MODE))
extern unsigned int element_precision (const_tree);
extern machine_mode element_mode (const_tree);
extern machine_mode vector_type_mode (const_tree);
extern unsigned int vector_element_bits (const_tree);