tree-optimization/105969 - FPE with array diagnostics

For a [0][0] array we have to be careful when dividing by the element
size which is zero for the outermost dimension.  Luckily the division
is only for an overflow check which is pointless for array size zero.

2022-06-15  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/105969
	* gimple-ssa-sprintf.cc (get_origin_and_offset_r): Avoid division
	by zero in overflow check.

	* gcc.dg/pr105969.c: New testcase.

(cherry picked from commit edb9330c29fe8a0a0b76df6fafd6a223a4d0e41f)

diff --git a/gcc/gimple-ssa-sprintf.cc b/gcc/gimple-ssa-sprintf.cc
index 9bd17bc..c0405ab 100644 (file)
--- a/gcc/gimple-ssa-sprintf.cc
+++ b/gcc/gimple-ssa-sprintf.cc
@@ -2319,7 +2319,7 @@ get_origin_and_offset_r (tree x, HOST_WIDE_INT *fldoff, HOST_WIDE_INT *fldsize,
 
        if (byteoff < HOST_WIDE_INT_MAX
            && elbytes < HOST_WIDE_INT_MAX
-           && byteoff / elbytes == idx)
+           && (elbytes == 0 || byteoff / elbytes == idx))
          {
            /* For in-bounds constant offsets into constant-sized arrays
               bump up *OFF, and for what's likely arrays or structs of

diff --git a/gcc/testsuite/gcc.dg/pr105969.c b/gcc/testsuite/gcc.dg/pr105969.c
new file mode 100644 (file)
index 0000000..52c63fc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr105969.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall" } */
+
+struct A
+{
+  char a[0][0][0];
+};
+extern struct A b[][2];
+void f (void)
+{
+  __builtin_sprintf (b[0][0].a[1][0], "%s", b[0][0].a[1][0]); /* { dg-warning "past the end" } */
+  /* { dg-warning "overlaps destination" "" { target *-*-* } .-1 } */
+}