[gcc r14-8913] lower-bitint: Fix up .{ADD,SUB}_OVERFLOW lowering

[gcc r14-8913] lower-bitint: Fix up .{ADD,SUB}_OVERFLOW lowering

[Jakub Jelinek]

https://gcc.gnu.org/g:d10c0dce53b2f1435fb66a570f15310baef5172d

commit r14-8913-gd10c0dce53b2f1435fb66a570f15310baef5172d
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sat Feb 10 12:52:23 2024 +0100

    lower-bitint: Fix up .{ADD,SUB}_OVERFLOW lowering
    
    torture/bitint-37.c test FAILed on i686-linux e.g. on
    signed _BitInt(575) + unsigned _BitInt(575) -> signed _BitInt(575)
    __builtin_add_overflow.  With 64-bit limbs, we use 4 .UADDC calls in
    the IL, 2 in a loop (which handles the first 8 limbs), then one partial
    limb (we use 63 bits from that) and finally last_ovf case due to the
    mixing of signed vs. unsigned.
    But with 32-bit limbs, we use 5 .UADDC calls in the IL, 2 in a loop (which
    handles the first 16 limbs), then one full limb above that, one partial
    (31 bits) and finally last_ovf case, and for the last_ovf case the code
    computed incorrect idx and so partly did the wrong thing, e.g. overwrote
    the result from the previous .UADDC.
    
    Fixed thusly.
    
    2024-02-10  Jakub Jelinek  <jakub@redhat.com>
    
            * gimple-lower-bitint.cc (itint_large_huge::lower_addsub_overflow): Fix
            computation of idx for i == 4 of bitint_prec_huge.

Diff:
---
 gcc/gimple-lower-bitint.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/gimple-lower-bitint.cc b/gcc/gimple-lower-bitint.cc
index e29d83193265..caa33e0aacf1 100644
--- a/gcc/gimple-lower-bitint.cc
+++ b/gcc/gimple-lower-bitint.cc
@@ -4031,7 +4031,7 @@ bitint_large_huge::lower_addsub_overflow (tree obj, gimple *stmt)
       if (kind != bitint_prec_huge)
 	idx = size_int (i);
       else if (i >= 2)
-	idx = size_int (fin + (i > 2));
+	idx = size_int (fin + i - 2);
       if (!last_ovf || i < cnt - 1)
 	{
 	  if (type0 != TREE_TYPE (arg0))