lower-bitint: Fix up handling of nested casts in mergeable stmt handling [PR112941]

The following patch fixes 2 issues in handling of casts for mergeable
stmts.
The first hunk fixes the case when we have two nested casts (typically
after optimization that is zero-extension of a sign-extension because
everything else should have been folded into a single cast).  If
the lowering of the outer cast needs to make the code conditional
(e.g.
  for (...)
    {
      if (idx <= 32)
        {
          if (idx < 32)
            { ... handle_operand (idx); ... }
          else
            { ... handle_operand (32); ... }
        }
      ...
    }
) and the lowering of the inner one as well, right now it creates invalid
SSA form, because even for the inner cast we need a PHI on the loop
and the PHI argument from the latch edge is a SSA_NAME initialized in
the conditionally executed bb.  The hunk fixes that by detecting such
a case and adding further PHI nodes at the end of the ifs such that
the right value propagates to the next loop iteration.  We can use
0 arguments for the other edges because the inner operand handling
is only done for the first set of iterations and then the other ifs take
over.

The rest fixes a case of again invalid SSA form, when for a sign extension
we need to use the 0 or -1 value initialized by earlier iteration in
a constant idx case, the code was using the value of the loop PHI argument
from latch edge rather than result; that is correct for cases expanded
in straight line code after the loop, but not inside of the loop for the
cases of handle_cast conditionals, there we should use PHI result.  This
is done in the second hunk and supported by the remaining hunks, where
it clears m_bb to tell the code we aren't in the loop anymore.

Note, this patch doesn't deal with similar problems during multiplication,
division, floating casts etc. where we just emit a library call.  I'll
need to make sure in that case we don't merge more than one cast per
operand.

2023-12-20  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/112941
	* gimple-lower-bitint.cc (bitint_large_huge::handle_cast): If
	save_cast_conditional, instead of adding assignment of t4 to
	m_data[save_data_cnt + 1] before m_gsi, add phi nodes such that
	t4 propagates to m_bb loop.  For constant idx, use
	m_data[save_data_cnt] rather than m_data[save_data_cnt + 1] if inside
	of the m_bb loop.
	(bitint_large_huge::lower_mergeable_stmt): Clear m_bb when no longer
	expanding inside of that loop.
	(bitint_large_huge::lower_comparison_stmt): Likewise.
	(bitint_large_huge::lower_addsub_overflow): Likewise.
	(bitint_large_huge::lower_mul_overflow): Likewise.
	(bitint_large_huge::lower_bit_query): Likewise.

	* gcc.dg/bitint-55.c: New test.

2 files changed, 161 insertions, 2 deletions

diff --git a/gcc/gimple-lower-bitint.cc b/gcc/gimple-lower-bitint.cc
index 696bba4..8b392b1 100644
--- a/gcc/gimple-lower-bitint.cc
+++ b/gcc/gimple-lower-bitint.cc
@@ -1401,8 +1401,29 @@ bitint_large_huge::handle_cast (tree lhs_type, tree rhs1, tree idx)
 	      add_phi_arg (phi, m_data[save_data_cnt], edge_false,
 			   UNKNOWN_LOCATION);
 	      add_phi_arg (phi, ext, edge_true_true, UNKNOWN_LOCATION);
-	      g = gimple_build_assign (m_data[save_data_cnt + 1], t4);
-	      insert_before (g);
+	      if (!save_cast_conditional)
+		{
+		  g = gimple_build_assign (m_data[save_data_cnt + 1], t4);
+		  insert_before (g);
+		}
+	      else
+		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 ? m_data[save_data_cnt + 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);
+		    if (e2)
+		      break;
+		    t4 = t5;
+		    bb = e1->dest;
+		  }
 	    }
 	  if (m_bitfld_load)
 	    {
@@ -1470,6 +1491,8 @@ bitint_large_huge::handle_cast (tree lhs_type, tree rhs1, tree idx)
 		m_data_cnt = tree_to_uhwi (m_data[save_data_cnt + 2]);
 	      if (TYPE_UNSIGNED (rhs_type))
 		t = build_zero_cst (m_limb_type);
+	      else if (m_bb)
+		t = m_data[save_data_cnt];
 	      else
 		t = m_data[save_data_cnt + 1];
 	    }
@@ -2586,6 +2609,7 @@ bitint_large_huge::lower_mergeable_stmt (gimple *stmt, tree_code &cmp_code,
 		m_gsi = gsi_after_labels (edge_bb);
 	      else
 		m_gsi = gsi_for_stmt (stmt);
+	      m_bb = NULL;
 	    }
 	}
     }
@@ -2712,6 +2736,7 @@ bitint_large_huge::lower_mergeable_stmt (gimple *stmt, tree_code &cmp_code,
 				     NULL_TREE, NULL_TREE);
 	      insert_before (g);
 	      m_gsi = gsi_for_stmt (stmt);
+	      m_bb = NULL;
 	    }
 	}
     }
@@ -2890,6 +2915,7 @@ bitint_large_huge::lower_comparison_stmt (gimple *stmt, tree_code &cmp_code,
 	  extract_true_false_edges_from_block (gsi_bb (m_gsi),
 					       &true_edge, &false_edge);
 	  m_gsi = gsi_after_labels (false_edge->dest);
+	  m_bb = NULL;
 	}
     }
 
@@ -4208,6 +4234,7 @@ bitint_large_huge::lower_addsub_overflow (tree obj, gimple *stmt)
 				     NULL_TREE, NULL_TREE);
 	      insert_before (g);
 	      m_gsi = gsi_for_stmt (final_stmt);
+	      m_bb = NULL;
 	    }
 	}
     }
@@ -4405,6 +4432,7 @@ bitint_large_huge::lower_mul_overflow (tree obj, gimple *stmt)
 						       &true_edge,
 						       &false_edge);
 		  m_gsi = gsi_after_labels (false_edge->dest);
+		  m_bb = NULL;
 		}
 	    }
 
@@ -4744,6 +4772,7 @@ bitint_large_huge::lower_bit_query (gimple *stmt)
 		    m_gsi = gsi_after_labels (edge_bb);
 		  else
 		    m_gsi = gsi_for_stmt (stmt);
+		  m_bb = NULL;
 		}
 	    }
 	}
@@ -4905,6 +4934,7 @@ bitint_large_huge::lower_bit_query (gimple *stmt)
 	      extract_true_false_edges_from_block (gsi_bb (m_gsi),
 						   &true_edge, &false_edge);
 	      m_gsi = gsi_after_labels (false_edge->dest);
+	      m_bb = NULL;
 	    }
 	}
     }
diff --git a/gcc/testsuite/gcc.dg/bitint-55.c b/gcc/testsuite/gcc.dg/bitint-55.c
new file mode 100644
index 0000000..29ddf50
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/bitint-55.c
@@ -0,0 +1,129 @@
+/* PR tree-optimization/112941 */
+/* { dg-do compile { target bitint } } */
+/* { dg-options "-std=c23 -O2" } */
+
+#if __BITINT_MAXWIDTH__ >= 4096
+void
+f1 (_BitInt(4096) *p, int r, _BitInt(115) s, _BitInt(128) t, _BitInt(231) u)
+{
+  p[0] += (unsigned _BitInt(2048)) r;
+  p[1] += (unsigned _BitInt(2048)) s;
+  p[2] += (unsigned _BitInt(2048)) t;
+  p[3] += (unsigned _BitInt(2048)) u;
+}
+
+void
+f2 (_BitInt(4094) *p, int r, _BitInt(115) s, _BitInt(128) t, _BitInt(231) u)
+{
+  p[0] -= (unsigned _BitInt(2048)) r;
+  p[1] -= (unsigned _BitInt(2048)) s;
+  p[2] -= (unsigned _BitInt(2048)) t;
+  p[3] -= (unsigned _BitInt(2048)) u;
+}
+
+void
+f3 (_BitInt(4096) *p, int r, _BitInt(115) s, _BitInt(128) t, _BitInt(231) u)
+{
+  p[0] += (unsigned _BitInt(2110)) r;
+  p[1] += (unsigned _BitInt(2110)) s;
+  p[2] += (unsigned _BitInt(2110)) t;
+  p[3] += (unsigned _BitInt(2110)) u;
+}
+
+void
+f4 (_BitInt(4094) *p, int r, _BitInt(115) s, _BitInt(128) t, _BitInt(231) u)
+{
+  p[0] -= (unsigned _BitInt(2110)) r;
+  p[1] -= (unsigned _BitInt(2110)) s;
+  p[2] -= (unsigned _BitInt(2110)) t;
+  p[3] -= (unsigned _BitInt(2110)) u;
+}
+
+void
+f5 (unsigned _BitInt(4096) *p, int r, _BitInt(115) s, _BitInt(128) t, _BitInt(231) u)
+{
+  p[0] += (unsigned _BitInt(2048)) r;
+  p[1] += (unsigned _BitInt(2048)) s;
+  p[2] += (unsigned _BitInt(2048)) t;
+  p[3] += (unsigned _BitInt(2048)) u;
+}
+
+void
+f6 (unsigned _BitInt(4094) *p, int r, _BitInt(115) s, _BitInt(128) t, _BitInt(231) u)
+{
+  p[0] -= (unsigned _BitInt(2048)) r;
+  p[1] -= (unsigned _BitInt(2048)) s;
+  p[2] -= (unsigned _BitInt(2048)) t;
+  p[3] -= (unsigned _BitInt(2048)) u;
+}
+
+void
+f7 (unsigned _BitInt(4096) *p, int r, _BitInt(115) s, _BitInt(128) t, _BitInt(231) u)
+{
+  p[0] += (unsigned _BitInt(2110)) r;
+  p[1] += (unsigned _BitInt(2110)) s;
+  p[2] += (unsigned _BitInt(2110)) t;
+  p[3] += (unsigned _BitInt(2110)) u;
+}
+
+void
+f8 (unsigned _BitInt(4094) *p, int r, _BitInt(115) s, _BitInt(128) t, _BitInt(231) u)
+{
+  p[0] -= (unsigned _BitInt(2110)) r;
+  p[1] -= (unsigned _BitInt(2110)) s;
+  p[2] -= (unsigned _BitInt(2110)) t;
+  p[3] -= (unsigned _BitInt(2110)) u;
+}
+
+#if __SIZEOF_INT128__
+void
+f9 (_BitInt(4096) *p, __int128 r)
+{
+  p[0] += (unsigned _BitInt(2048)) r;
+}
+
+void
+f10 (_BitInt(4094) *p, __int128 r)
+{
+  p[0] -= (unsigned _BitInt(2048)) r;
+}
+
+void
+f11 (_BitInt(4096) *p, __int128 r)
+{
+  p[0] += (unsigned _BitInt(2110)) r;
+}
+
+void
+f12 (_BitInt(4094) *p, __int128 r)
+{
+  p[0] -= (unsigned _BitInt(2110)) r;
+}
+
+void
+f13 (unsigned _BitInt(4096) *p, __int128 r)
+{
+  p[0] += (unsigned _BitInt(2048)) r;
+}
+
+void
+f14 (unsigned _BitInt(4094) *p, __int128 r)
+{
+  p[0] -= (unsigned _BitInt(2048)) r;
+}
+
+void
+f15 (unsigned _BitInt(4096) *p, __int128 r)
+{
+  p[0] += (unsigned _BitInt(2110)) r;
+}
+
+void
+f16 (unsigned _BitInt(4094) *p, __int128 r)
+{
+  p[0] -= (unsigned _BitInt(2110)) r;
+}
+#endif
+#else
+int i;
+#endif