c/95141 - fix bogus integer overflow warning

This fixes an integer overflow warning that ultimatively happens because
of TREE_OVERFLOW propagating through transforms and the existing guard
against this,

375           if (TREE_OVERFLOW_P (ret)
376               && !TREE_OVERFLOW_P (op0)
377               && !TREE_OVERFLOW_P (op1))
378             overflow_warning (EXPR_LOC_OR_LOC (expr, input_location,

being insufficient.  Rather than trying to use sth like walk_tree to
exhaustively walk operands (with the possibility of introducing
quadraticness when folding larger expressions recursively) the
following amends the above with an ad-hoc test for a binary op0
with a possibly constant op1.

2020-05-30  Richard Biener  <rguenther@suse.de>

	PR c/95141
gcc/c
	* c-fold.c (c_fully_fold_internal): Enhance guard on
	overflow_warning.

gcc/testsuite
	* gcc.dg/pr95141.c: New testcase.

gcc/ChangeLog

@@ -1,3 +1,9 @@
+2020-05-30  Richard Biener  <rguenther@suse.de>
+
+	PR c/95141
+	* c-fold.c (c_fully_fold_internal): Enhance guard on
+	overflow_warning.
+
 2020-05-20  Kito Cheng  <kito.cheng@sifive.com>
 
 	PR target/90811

gcc/c/c-fold.c

@@ -374,6 +374,7 @@ c_fully_fold_internal (tree expr, bool in_init, bool *maybe_const_operands,
 	ret = fold (expr);
       if (TREE_OVERFLOW_P (ret)
 	  && !TREE_OVERFLOW_P (op0)
+	  && !(BINARY_CLASS_P (op0) && TREE_OVERFLOW_P (TREE_OPERAND (op0, 1)))
 	  && !TREE_OVERFLOW_P (op1))
 	overflow_warning (EXPR_LOC_OR_LOC (expr, input_location), ret, expr);
       if (code == LSHIFT_EXPR

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2020-05-30  Richard Biener  <rguenther@suse.de>
+
+	PR c/95141
+	* gcc.dg/pr95141.c: New testcase.
+
 2020-05-19  Alex Coplan  <alex.coplan@arm.com>
 
 	PR target/94591

gcc/testsuite/gcc.dg/pr95141.c

@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+
+#include <stdint.h>
+
+uint64_t test(uint8_t IA1)
+{
+  return (uint8_t)(IA1 & 158) & 1UL; /* { dg-bogus "integer overflow" } */
+}