Fix PR 106900: array-bounds warning inside simplify_builtin_call

The problem here is that VRP cannot figure out isize could not be 0
due to using integer_zerop. This patch removes the use of integer_zerop
and instead checks for 0 directly after converting the tree to
an unsigned HOST_WIDE_INT. This allows VRP to figure out isize is not 0
and `isize - 1` will always be >= 0.

This patch is just to avoid the warning that GCC could produce sometimes
and does not change any code generation or even VRP.

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

gcc/ChangeLog:

	* tree-ssa-forwprop.cc (simplify_builtin_call): Check
	against 0 instead of calling integer_zerop.

diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index 06f19868ade7ec51658afe58f326148c6e3216b0..0326e6733e8638c2b09d0b7556f976c5f2f4ec23 100644 (file)
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -1231,14 +1231,14 @@ simplify_builtin_call (gimple_stmt_iterator *gsi_p, tree callee2)
          tree size = gimple_call_arg (stmt2, 2);
          /* Size must be a constant which is <= UNITS_PER_WORD and
             <= the string length.  */
-         if (TREE_CODE (size) != INTEGER_CST || integer_zerop (size))
+         if (TREE_CODE (size) != INTEGER_CST)
            break;
 
          if (!tree_fits_uhwi_p (size))
            break;
 
          unsigned HOST_WIDE_INT sz = tree_to_uhwi (size);
-         if (sz > UNITS_PER_WORD || sz >= slen)
+         if (sz == 0 || sz > UNITS_PER_WORD || sz >= slen)
            break;
 
          tree ch = gimple_call_arg (stmt2, 1);