[PATCH] tree-optimization/98640 - fix bogus sign-extension with VN

[Richard Biener]

VN tried to express a sign extension from int to long of
a trucated quantity with a plain conversion but that loses the
truncation.  Since there's no single operand doing truncate plus
sign extend (there was a proposed SEXT_EXPR to do that at some
point mapping to RTL sign_extract) don't bother to appropriately
model this with two ops (which the VN insert machinery doesn't
handle and which is unlikely to CSE fully).

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

2021-01-13  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/98640
	* tree-ssa-sccvn.c (visit_nary_op): Do not try to
	handle plus or minus from a truncated operand to be
	sign-extended.

	* gcc.dg/torture/pr98640.c: New testcase.
---
 gcc/testsuite/gcc.dg/torture/pr98640.c | 22 ++++++++++++++++++++++
 gcc/tree-ssa-sccvn.c                   | 15 +++++++++------
 2 files changed, 31 insertions(+), 6 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr98640.c

diff --git a/gcc/testsuite/gcc.dg/torture/pr98640.c b/gcc/testsuite/gcc.dg/torture/pr98640.c
new file mode 100644
index 00000000000..b187781d614
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr98640.c
@@ -0,0 +1,22 @@
+/* { dg-do run } */
+/* { dg-require-effective-target stdint_types } */
+
+#include <stdint.h>
+
+uint64_t var_0 = 18128133247277979402ULL;
+int64_t var_14 = 6557021550272328915LL;
+uint64_t var_83 = 10966786425750692026ULL;
+
+void test()
+{
+  var_14 = var_0 + (_Bool)7;
+  var_83 = 1 + (int)var_0; // 1 + 888395530
+}
+
+int main()
+{
+  test();
+  if (var_83 != 888395531)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index 0ba846f0be2..588f1b82478 100644
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -4681,7 +4681,7 @@ visit_copy (tree lhs, tree rhs)
    is the same.  */
 
 static tree
-valueized_wider_op (tree wide_type, tree op)
+valueized_wider_op (tree wide_type, tree op, bool allow_truncate)
 {
   if (TREE_CODE (op) == SSA_NAME)
     op = vn_valueize (op);
@@ -4695,7 +4695,7 @@ valueized_wider_op (tree wide_type, tree op)
     return tem;
 
   /* Or the op is truncated from some existing value.  */
-  if (TREE_CODE (op) == SSA_NAME)
+  if (allow_truncate && TREE_CODE (op) == SSA_NAME)
     {
       gimple *def = SSA_NAME_DEF_STMT (op);
       if (is_gimple_assign (def)
@@ -4760,12 +4760,15 @@ visit_nary_op (tree lhs, gassign *stmt)
 		  || gimple_assign_rhs_code (def) == MULT_EXPR))
 	    {
 	      tree ops[3] = {};
+	      /* When requiring a sign-extension we cannot model a
+		 previous truncation with a single op so don't bother.  */
+	      bool allow_truncate = TYPE_UNSIGNED (TREE_TYPE (rhs1));
 	      /* Either we have the op widened available.  */
-	      ops[0] = valueized_wider_op (type,
-					   gimple_assign_rhs1 (def));
+	      ops[0] = valueized_wider_op (type, gimple_assign_rhs1 (def),
+					   allow_truncate);
 	      if (ops[0])
-		ops[1] = valueized_wider_op (type,
-					     gimple_assign_rhs2 (def));
+		ops[1] = valueized_wider_op (type, gimple_assign_rhs2 (def),
+					     allow_truncate);
 	      if (ops[0] && ops[1])
 		{
 		  ops[0] = vn_nary_op_lookup_pieces
-- 
2.26.2