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lower-bitint: Fix up lowering of huge _BitInt 0 PHI args [PR113120]

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The PHI argument expansion of INTEGER_CSTs where bitint_min_cst_precision
returns significantly smaller precision than the PHI result precision is
optimized by loading the much smaller constant (if any) from memory and
then either setting the remaining limbs to {} or calling memset with -1.
The case where no constant is loaded (i.e. c == NULL) is when the
INTEGER_CST is 0 or all_ones - in that case we can just set all the limbs
to {} or call memset with -1 on everything.
While for the all ones extension case that is what the code was already
doing, I missed one spot in the zero extension case, where constricting
the offset of the MEM_REF lhs of the = {} store it was using unconditionally
the byte size of c, which obviously doesn't work if c is NULL.  In that case
we want to use zero offset.

2024-01-08  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/113120
	* gimple-lower-bitint.cc (gimple_lower_bitint): Fix handling of very
	large _BitInt zero INTEGER_CST PHI argument.

	* gcc.dg/bitint-62.c: New test.
This commit is contained in:
Jakub Jelinek 2024-01-08 13:58:28 +01:00
parent 7590d975ec
commit efef8d7ff4
2 changed files with 38 additions and 2 deletions
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6
gcc/gimple-lower-bitint.cc
View file

@ -6606,8 +6606,12 @@ gimple_lower_bitint (void)
= build_array_type_nelts (large_huge.m_limb_type,
nelts);
tree ptype = build_pointer_type (TREE_TYPE (v1));
tree off = fold_convert (ptype,
tree off;
if (c)
off = fold_convert (ptype,
TYPE_SIZE_UNIT (TREE_TYPE (c)));
else
off = build_zero_cst (ptype);
tree vd = build2 (MEM_REF, vtype,
build_fold_addr_expr (v1), off);
g = gimple_build_assign (vd, build_zero_cst (vtype));

32
gcc/testsuite/gcc.dg/bitint-62.c Normal file
View file

@ -0,0 +1,32 @@
/* PR tree-optimization/113120 */
/* { dg-do compile { target bitint } } */
/* { dg-options "-std=c23 -O2" } */
_BitInt(8) a;
_BitInt(55) b;
#if __BITINT_MAXWIDTH__ >= 401
static __attribute__((noinline, noclone)) void
foo (unsigned _BitInt(1) c, _BitInt(401) d)
{
c /= d << b;
a = c;
}
void
bar (void)
{
foo (1, 4);
}
#endif
#if __BITINT_MAXWIDTH__ >= 6928
_BitInt(6928)
baz (int x, _BitInt(6928) y)
{
if (x)
return y;
else
return 0;
}
#endif