lower-bitint: Punt .*_OVERFLOW optimization if cast from IMAGPART_EXPR appears before REALPART_EXPR [PR113119]

_BitInt lowering for .{ADD,SUB,MUL}_OVERFLOW calls which have both
REALPART_EXPR and IMAGPART_EXPR used and have a cast from the IMAGPART_EXPR
to a boolean or normal integral type lowers them at the point of
the REALPART_EXPR statement (which is especially needed if the lhs of
the call is complex with large/huge _BitInt element type); we emit the
stmt to set the lhs of the cast at the same spot as well.
Normally, the lowering of __builtin_{add,sub,mul}_overflow arranges
the REALPART_EXPR to come before IMAGPART_EXPR, followed by cast from that,
but as the testcase shows, a redundant __builtin_*_overflow call and VN
can reorder those and we then ICE because the def-stmt of the former cast
from IMAGPART_EXPR may appear after its uses.
We already check that all of REALPART_EXPR, IMAGPART_EXPR and the cast
from the latter appear in the same bb as the .{ADD,SUB,MUL}_OVERFLOW call
in the optimization, the following patch just extends it to make sure
cast appears after REALPART_EXPR; if not, we punt on the optimization and
expand it as a store of a complex _BitInt on the location of the ifn call.
Only the testcase in the testsuite is changed by the patch, all other
__builtin_*_overflow* calls in the bitint* tests (and there are quite a few)
have REALPART_EXPR first.

2024-01-08  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/113119
	* gimple-lower-bitint.cc (optimizable_arith_overflow): Punt if
	both REALPART_EXPR and cast from IMAGPART_EXPR appear, but cast
	is before REALPART_EXPR.

	* gcc.dg/bitint-61.c: New test.

2 files changed, 42 insertions, 1 deletions

diff --git a/gcc/gimple-lower-bitint.cc b/gcc/gimple-lower-bitint.cc
index 9a80f93..3869a16 100644
--- a/gcc/gimple-lower-bitint.cc
+++ b/gcc/gimple-lower-bitint.cc
@@ -305,6 +305,7 @@ optimizable_arith_overflow (gimple *stmt)
   imm_use_iterator ui;
   use_operand_p use_p;
   int seen = 0;
+  gimple *realpart = NULL, *cast = NULL;
   FOR_EACH_IMM_USE_FAST (use_p, ui, lhs)
     {
       gimple *g = USE_STMT (use_p);
@@ -317,6 +318,7 @@ optimizable_arith_overflow (gimple *stmt)
 	  if ((seen & 1) != 0)
 	    return 0;
 	  seen |= 1;
+	  realpart = g;
 	}
       else if (gimple_assign_rhs_code (g) == IMAGPART_EXPR)
 	{
@@ -338,13 +340,35 @@ optimizable_arith_overflow (gimple *stmt)
 	  if (!INTEGRAL_TYPE_P (TREE_TYPE (lhs2))
 	      || TREE_CODE (TREE_TYPE (lhs2)) == BITINT_TYPE)
 	    return 0;
+	  cast = use_stmt;
 	}
       else
 	return 0;
     }
   if ((seen & 2) == 0)
     return 0;
-  return seen == 3 ? 2 : 1;
+  if (seen == 3)
+    {
+      /* Punt if the cast stmt appears before realpart stmt, because
+	 if both appear, the lowering wants to emit all the code
+	 at the location of realpart stmt.  */
+      gimple_stmt_iterator gsi = gsi_for_stmt (realpart);
+      unsigned int cnt = 0;
+      do
+	{
+	  gsi_prev_nondebug (&gsi);
+	  if (gsi_end_p (gsi) || gsi_stmt (gsi) == cast)
+	    return 0;
+	  if (gsi_stmt (gsi) == stmt)
+	    return 2;
+	  /* If realpart is too far from stmt, punt as well.
+	     Usually it will appear right after it.  */
+	  if (++cnt == 32)
+	    return 0;
+	}
+      while (1);
+    }
+  return 1;
 }
 
 /* If STMT is some kind of comparison (GIMPLE_COND, comparison assignment)
diff --git a/gcc/testsuite/gcc.dg/bitint-61.c b/gcc/testsuite/gcc.dg/bitint-61.c
new file mode 100644
index 0000000..2b2708a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/bitint-61.c
@@ -0,0 +1,17 @@
+/* PR tree-optimization/113119 */
+/* { dg-do compile { target bitint } } */
+/* { dg-options "-std=c23 -O2" } */
+
+_BitInt(8) b;
+_Bool c;
+#if __BITINT_MAXWIDTH__ >= 8445
+_BitInt(8445) a;
+
+void
+foo (_BitInt(4058) d)
+{
+  c = __builtin_add_overflow (a, 0ULL, &d);
+  __builtin_add_overflow (a, 0ULL, &d);
+  b = d;
+}
+#endif