[gcc r14-6050] lower-bitint: Fix up handle_operand_addr for 0 constants [PR112771]

[Jakub Jelinek]

https://gcc.gnu.org/g:9bfebcb1b7ae4e7160644f2104424d6bab4a23f7

commit r14-6050-g9bfebcb1b7ae4e7160644f2104424d6bab4a23f7
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Dec 1 10:55:49 2023 +0100

    lower-bitint: Fix up handle_operand_addr for 0 constants [PR112771]
    
    handle_operand_addr for INTEGER_CSTs uses wi::min_precision (UNSIGNED
    for non-negative constants, SIGNED for negative ones) and from that
    computes mp as minimum number of limbs which can represent that value,
    and in some cases creates a test BITINT_TYPE with that precision to
    categorize it and decide based on that what types to use on the constant
    emitted into memory.  For the actual precisions (what will be passed
    to libgcc) it actually already uses MAX/MIN to adjust the corner cases:
              *prec = MAX (min_prec, 1);
    ...
              *prec = MIN ((int) -min_prec, -2);
    but for integer_zerop min_prec will be 0,
    mp = CEIL (min_prec, limb_prec) * limb_prec;
    will be also 0 and we ICE trying to build unsigned BITINT_TYPE with
    0 precision.
    
    Fixed thusly by noting even 0 has to be encoded at least as one limb.
    
    2023-12-01  Jakub Jelinek  <jakub@redhat.com>
    
            PR middle-end/112771
            * gimple-lower-bitint.cc (bitint_large_huge::handle_operand_addr):
            Use mp = 1 if it is zero.
    
            * gcc.dg/bitint-44.c: New test.

Diff:
---
 gcc/gimple-lower-bitint.cc       |  2 ++
 gcc/testsuite/gcc.dg/bitint-44.c | 10 ++++++++++
 2 files changed, 12 insertions(+)

diff --git a/gcc/gimple-lower-bitint.cc b/gcc/gimple-lower-bitint.cc
index 7c8c640ab21..d0e24cbb621 100644
--- a/gcc/gimple-lower-bitint.cc
+++ b/gcc/gimple-lower-bitint.cc
@@ -2179,6 +2179,8 @@ bitint_large_huge::handle_operand_addr (tree op, gimple *stmt,
 	  *prec = MIN ((int) -min_prec, -2);
 	}
       mp = CEIL (min_prec, limb_prec) * limb_prec;
+      if (mp == 0)
+	mp = 1;
       if (mp >= (unsigned) TYPE_PRECISION (TREE_TYPE (op)))
 	type = TREE_TYPE (op);
       else
diff --git a/gcc/testsuite/gcc.dg/bitint-44.c b/gcc/testsuite/gcc.dg/bitint-44.c
new file mode 100644
index 00000000000..d1f34d02961
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/bitint-44.c
@@ -0,0 +1,10 @@
+/* PR middle-end/112771 */
+/* { dg-do compile { target bitint575 } } */
+/* { dg-options "-std=c23" } */
+
+_BitInt(575)
+foo (_BitInt(575) a)
+{
+  a /= 0;	/* { dg-warning "division by zero" } */
+  return a;
+}