[gcc r14-9570] bitint: Fix handling of conditional bitfield loads [PR114365]

[Jakub Jelinek via Gcc-cvs]

https://gcc.gnu.org/g:456e10f28b36aa417e0db145556831c4f979fbd7

commit r14-9570-g456e10f28b36aa417e0db145556831c4f979fbd7
Author: Jakub Jelinek <ja...@redhat.com>
Date:   Wed Mar 20 10:55:07 2024 +0100

    bitint: Fix handling of conditional bitfield loads [PR114365]
    
    For the m_var_msb (aka left shift) case of large/huge _BitInt bitfield loads
    handle_load adds a PHI node, but I forgot to actually update the temporary
    the code later on uses, so the PHI result was unused and the code
    incorrectly used something that wasn't valid SSA form.
    In particular, we emitted
      if (_29 != 2)
        goto <bb 4>; [80.00%]
      else
        goto <bb 5>; [20.00%]
    
      <bb 4> [local count: 1073741824]:
      _33 = VIEW_CONVERT_EXPR<unsigned long[3]>(s.D.2771)[_31];
    
      <bb 5> [local count: 1073741824]:
      # _34 = PHI <_33(4), 0(3)>
      _35 = _32 >> 31;
      _36 = _33 << 33;
      _37 = _36 | _35;
      _38 = _37 << _19;
    where instead of _33 the _36 def stmt should be using _34.
    
    Fixed thusly.
    
    2024-03-20  Jakub Jelinek  <ja...@redhat.com>
    
            PR tree-optimization/114365
            * gimple-lower-bitint.cc (bitint_large_huge::handle_load): When 
adding
            a PHI node, set iv2 to its result afterwards.
    
            * gcc.dg/bitint-102.c: New test.

Diff:
---
 gcc/gimple-lower-bitint.cc        |  1 +
 gcc/testsuite/gcc.dg/bitint-102.c | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/gcc/gimple-lower-bitint.cc b/gcc/gimple-lower-bitint.cc
index 40d814e5c38..1ce13ca2579 100644
--- a/gcc/gimple-lower-bitint.cc
+++ b/gcc/gimple-lower-bitint.cc
@@ -2026,6 +2026,7 @@ bitint_large_huge::handle_load (gimple *stmt, tree idx)
              add_phi_arg (phi, build_zero_cst (m_limb_type),
                           edge_false, UNKNOWN_LOCATION);
              m_gsi = gsi_after_labels (edge_true->dest);
+             iv2 = iv3;
            }
        }
       g = gimple_build_assign (make_ssa_name (m_limb_type), RSHIFT_EXPR,
diff --git a/gcc/testsuite/gcc.dg/bitint-102.c 
b/gcc/testsuite/gcc.dg/bitint-102.c
new file mode 100644
index 00000000000..9f9861ee2be
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/bitint-102.c
@@ -0,0 +1,18 @@
+/* PR tree-optimization/114365 */
+/* { dg-do compile { target bitint } } */
+/* { dg-options "-std=c23 -O2" } */
+
+struct S {
+  int : 31;
+#if __BITINT_MAXWIDTH__ >= 129
+  _BitInt(129) b : 129;
+#else
+  _BitInt(63) b : 63;
+#endif
+} s;
+
+void
+foo (int a)
+{
+  s.b <<= a;
+}