match.pd: Fix up __builtin_*_overflow arg demotion [PR102207]

My earlier patch to demote arguments of __builtin_*_overflow unfortunately
caused a wrong-code regression.  The builtins operate on infinite precision
arguments, outer_prec > inner_prec signed -> signed, unsigned -> unsigned
promotions there are just repeating the sign or 0s and can be demoted,
similarly unsigned -> signed which also is repeating 0s, but as the
testcase shows, signed -> unsigned promotions need to be preserved (unless
we'd know the inner arguments can't be negative), because for negative
numbers such promotion sets the outer_prec -> inner_prec bits to 1 bit the
bits above that to 0 in the infinite precision.

So, the following patch avoids the demotions for the signed -> unsigned
promotions.

2021-09-06  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/102207
	* match.pd: Don't demote operands of IFN_{ADD,SUB,MUL}_OVERFLOW if they
	were promoted from signed to wider unsigned type.

	* gcc.dg/pr102207.c: New test.

diff --git a/gcc/match.pd b/gcc/match.pd
index cc7809dfe0fa80e5707c309d711ce9b9701e8727..008f7758c96f3e00083962e06766374243fba75f 100644 (file)
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -5608,13 +5608,15 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
   (ovf (convert@2 @0) @1)
   (if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
        && INTEGRAL_TYPE_P (TREE_TYPE (@2))
-       && TYPE_PRECISION (TREE_TYPE (@2)) > TYPE_PRECISION (TREE_TYPE (@0)))
+       && TYPE_PRECISION (TREE_TYPE (@2)) > TYPE_PRECISION (TREE_TYPE (@0))
+       && (!TYPE_UNSIGNED (TREE_TYPE (@2)) || TYPE_UNSIGNED (TREE_TYPE (@0))))
    (ovf @0 @1)))
  (simplify
   (ovf @1 (convert@2 @0))
   (if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
        && INTEGRAL_TYPE_P (TREE_TYPE (@2))
-       && TYPE_PRECISION (TREE_TYPE (@2)) > TYPE_PRECISION (TREE_TYPE (@0)))
+       && TYPE_PRECISION (TREE_TYPE (@2)) > TYPE_PRECISION (TREE_TYPE (@0))
+       && (!TYPE_UNSIGNED (TREE_TYPE (@2)) || TYPE_UNSIGNED (TREE_TYPE (@0))))
    (ovf @1 @0))))
 
 /* Simplification of math builtins.  These rules must all be optimizations

diff --git a/gcc/testsuite/gcc.dg/pr102207.c b/gcc/testsuite/gcc.dg/pr102207.c
new file mode 100644 (file)
index 0000000..08540d0
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr102207.c
@@ -0,0 +1,24 @@
+/* PR tree-optimization/102207 */
+/* { dg-do run { target int128 } } */
+/* { dg-options "-O2" } */
+
+typedef unsigned __int128 u128;
+
+u128
+foo (unsigned short a)
+{
+  u128 g;
+  __builtin_sub_overflow ((unsigned long long) -a, 1, &g);
+  return g;
+}
+
+int
+main ()
+{
+  if (__SIZEOF_LONG_LONG__ * __CHAR_BIT__ != 64
+      || __SIZEOF_SHORT__ * __CHAR_BIT__ != 16)
+    return 0;
+  if (foo (1) != 0xfffffffffffffffeULL)
+    __builtin_abort ();
+  return 0;
+}