bitint: Handle m_bitfld_load cast in outer m_cast_conditional [PR114555]

We ICE on the following testcase, because we use result of a PHI node
which is only conditional because of a m_cast_conditional on the outermost
loops PHI node argument and so is invalid SSA form.

The following patch fixes it like similar cases elsewhere by adding
needed intervening PHI(s).

2024-04-04  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/114555
	* gimple-lower-bitint.cc (bitint_large_huge::handle_cast): For
	m_bitfld_load and save_cast_conditional add any needed PHIs
	and adjust t4 accordingly.

	* gcc.dg/bitint-103.c: New test.
	* gcc.dg/bitint-104.c: New test.

3 files changed, 52 insertions, 1 deletions

diff --git a/gcc/gimple-lower-bitint.cc b/gcc/gimple-lower-bitint.cc
index 40a1084..1afd4de 100644
--- a/gcc/gimple-lower-bitint.cc
+++ b/gcc/gimple-lower-bitint.cc
@@ -1506,7 +1506,7 @@ bitint_large_huge::handle_cast (tree lhs_type, tree rhs1, tree idx)
 	  if (m_bitfld_load)
 	    {
 	      tree t4;
-	      if (!save_first)
+	      if (!save_first && !save_cast_conditional)
 		t4 = m_data[m_bitfld_load + 1];
 	      else
 		t4 = make_ssa_name (m_limb_type);
@@ -1519,6 +1519,24 @@ bitint_large_huge::handle_cast (tree lhs_type, tree rhs1, tree idx)
 	      if (edge_true_true)
 		add_phi_arg (phi, m_data[m_bitfld_load], edge_true_true,
 			     UNKNOWN_LOCATION);
+	      if (save_cast_conditional)
+		for (basic_block bb = gsi_bb (m_gsi);;)
+		  {
+		    edge e1 = single_succ_edge (bb);
+		    edge e2 = find_edge (e1->dest, m_bb), e3;
+		    tree t5 = ((e2 && !save_first) ? m_data[m_bitfld_load + 1]
+			       : make_ssa_name (m_limb_type));
+		    phi = create_phi_node (t5, e1->dest);
+		    edge_iterator ei;
+		    FOR_EACH_EDGE (e3, ei, e1->dest->preds)
+		      add_phi_arg (phi, (e3 == e1 ? t4
+					 : build_zero_cst (m_limb_type)),
+				   e3, UNKNOWN_LOCATION);
+		    t4 = t5;
+		    if (e2)
+		      break;
+		    bb = e1->dest;
+		  }
 	      m_data[m_bitfld_load] = t4;
 	      m_data[m_bitfld_load + 2] = t4;
 	      m_bitfld_load = 0;
diff --git a/gcc/testsuite/gcc.dg/bitint-103.c b/gcc/testsuite/gcc.dg/bitint-103.c
new file mode 100644
index 0000000..4d81049
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/bitint-103.c
@@ -0,0 +1,16 @@
+/* PR tree-optimization/114555 */
+/* { dg-do compile { target bitint } } */
+/* { dg-options "-std=c23 -O2" } */
+
+#if __BITINT_MAXWIDTH__ >= 1225
+struct S { _BitInt(512) : 98; _BitInt(1225) b : 509; } s;
+_BitInt(1225) a;
+#endif
+
+void
+foo (void)
+{
+#if __BITINT_MAXWIDTH__ >= 1225
+  a ^= (unsigned _BitInt(1025)) s.b;
+#endif
+}
diff --git a/gcc/testsuite/gcc.dg/bitint-104.c b/gcc/testsuite/gcc.dg/bitint-104.c
new file mode 100644
index 0000000..b4aac83
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/bitint-104.c
@@ -0,0 +1,17 @@
+/* PR tree-optimization/114555 */
+/* { dg-do compile { target bitint } } */
+/* { dg-options "-std=c23 -O -fno-tree-forwprop" } */
+
+#if __BITINT_MAXWIDTH__ >= 4139
+struct S { _BitInt(31) : 6; _BitInt(513) b : 241; } s;
+_BitInt(4139) a;
+#endif
+
+void
+foo (void)
+{
+#if __BITINT_MAXWIDTH__ >= 4139
+  int i = 0;
+  a -= s.b << i;
+#endif
+}