[Bug tree-optimization/101260] [10/11 Regression] Backport 27381e78925 to GCC 11

["stefansf at linux dot ibm.com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101260

--- Comment #7 from Stefan Schulze Frielinghaus <stefansf at linux dot ibm.com> ---
I had a look at the optimized tree output which looks good to me. However, I
see that split2 transforms

(insn 218 222 114 15 (set (reg/v:TI 10 %r10 [orig:87 a ] [87])
        (reg/v:TI 18 %f4 [orig:87 a ] [87])) 1466 {movti}
     (nil))

into

(insn 234 222 235 15 (set (reg:DI 10 %r10 [ a ])
        (reg:DI 18 %f4)) 1467 {*movdi_64}
     (nil))
(insn 235 234 114 15 (set (reg:DI 11 %r11 [orig:87 a+8 ] [87])
        (unspec:DI [
                (reg:V2DI 18 %f4)
                (const_int 1 [0x1])
            ] UNSPEC_VEC_EXTRACT)) 495 {*vec_extractv2di}
     (nil))

which might be wrong. If I swap r10 by r11 via

diff --git a/gcc/config/s390/s390.md b/gcc/config/s390/s390.md
index 7faf775fbf2..0319934062a 100644
--- a/gcc/config/s390/s390.md
+++ b/gcc/config/s390/s390.md
@@ -1747,8 +1747,8 @@
    (set (match_dup 3) (unspec:DI [(match_dup 5) (const_int 1)]
                                 UNSPEC_VEC_EXTRACT))]
 {
-  operands[2] = operand_subword (operands[0], 0, 0, TImode);
-  operands[3] = operand_subword (operands[0], 1, 0, TImode);
+  operands[2] = operand_subword (operands[0], 1, 0, TImode);
+  operands[3] = operand_subword (operands[0], 0, 0, TImode);
   operands[4] = gen_rtx_REG (DImode, REGNO (operands[1]));
   operands[5] = gen_rtx_REG (V2DImode, REGNO (operands[1]));
 })

then the compiled program just runs fine. However, I'm not sure whether this
fixes the problem or just the symptoms. I will come back to this tomorrow.