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ifcvt: Don't lower bitfields with non-constant offsets [PR 111882]

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This patch stops lowering of bitfields by ifcvt when they have non-constant
offsets as we are not likely to be able to do anything useful with those during
vectorization.  That also fixes the issue reported in PR 111882, which was
being caused by an offset with a side-effect being lowered, but constants have
no side-effects so we will no longer run into that problem.

gcc/ChangeLog:

	PR tree-optimization/111882
	* tree-if-conv.cc (get_bitfield_rep): Return NULL_TREE for bitfields
	with non-constant offsets.

gcc/testsuite/ChangeLog:

	* gcc.dg/vect/pr111882.c: New test.
This commit is contained in:
Andre Vieira 2023-10-20 17:02:32 +01:00
parent c29d55234e
commit 24cf1f600b
2 changed files with 26 additions and 1 deletions
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15
gcc/testsuite/gcc.dg/vect/pr111882.c Normal file
View File

@ -0,0 +1,15 @@
/* { dg-do compile } */
/* { dg-additional-options { -fdump-tree-ifcvt-all } } */
static void __attribute__((noipa)) f(int n) {
int i, j;
struct S { char d[n]; int a; int b : 17; int c : 12; };
struct S A[100][1111];
for (i = 0; i < 100; i++) {
asm volatile("" : : "g"(&A[0][0]) : "memory");
for (j = 0; j < 1111; j++) A[i][j].b = 2;
}
}
void g(void) { f(1); }
/* { dg-final { scan-tree-dump-not "Bitfield OK to lower" "ifcvt" } } */

12
gcc/tree-if-conv.cc
View File

@ -3495,6 +3495,7 @@ get_bitfield_rep (gassign *stmt, bool write, tree *bitpos,
: gimple_assign_rhs1 (stmt);
tree field_decl = TREE_OPERAND (comp_ref, 1);
tree ref_offset = component_ref_field_offset (comp_ref);
tree rep_decl = DECL_BIT_FIELD_REPRESENTATIVE (field_decl);
/* Bail out if the representative is not a suitable type for a scalar
@ -3509,6 +3510,15 @@ get_bitfield_rep (gassign *stmt, bool write, tree *bitpos,
if (compare_tree_int (DECL_SIZE (field_decl), bf_prec) != 0)
return NULL_TREE;
if (TREE_CODE (DECL_FIELD_OFFSET (rep_decl)) != INTEGER_CST
|| TREE_CODE (ref_offset) != INTEGER_CST)
{
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "\t Bitfield NOT OK to lower,"
" offset is non-constant.\n");
return NULL_TREE;
}
if (struct_expr)
*struct_expr = TREE_OPERAND (comp_ref, 0);
@ -3529,7 +3539,7 @@ get_bitfield_rep (gassign *stmt, bool write, tree *bitpos,
the structure and the container from the number of bits from the start
of the structure and the actual bitfield member. */
tree bf_pos = fold_build2 (MULT_EXPR, bitsizetype,
DECL_FIELD_OFFSET (field_decl),
ref_offset,
build_int_cst (bitsizetype, BITS_PER_UNIT));
bf_pos = fold_build2 (PLUS_EXPR, bitsizetype, bf_pos,
DECL_FIELD_BIT_OFFSET (field_decl));