[gcc r12-8579] tree-optimization/105969 - FPE with array diagnostics

[gcc r12-8579] tree-optimization/105969 - FPE with array diagnostics

[Richard Biener]

https://gcc.gnu.org/g:4f34a9e8d5ffcef99a212180d58718b00bdbb7d2

commit r12-8579-g4f34a9e8d5ffcef99a212180d58718b00bdbb7d2
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Jun 15 10:54:48 2022 +0200

    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:
---
 gcc/gimple-ssa-sprintf.cc       |  2 +-
 gcc/testsuite/gcc.dg/pr105969.c | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/gcc/gimple-ssa-sprintf.cc b/gcc/gimple-ssa-sprintf.cc
index 9bd17bcca92..c0405ab32db 100644
--- 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
index 00000000000..52c63fc2efe
--- /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 } */
+}