From 820f0940d7ace1306430a9dcf1bd9577508a7a7e Mon Sep 17 00:00:00 2001
From: Martin Sebor <msebor@redhat.com>
Date: Tue, 24 Aug 2021 10:49:11 -0600
Subject: Reset PHI base0 flag if it's clear in any argument [PR101977, ...]

Resolves:
PR middle-end/101600 - Spurious -Warray-bounds downcasting a polymorphic pointer
PR middle-end/101977 - bogus -Warray-bounds on a negative index into a parameter in conditional with null

gcc/ChangeLog:

	PR middle-end/101600
	PR middle-end/101977
	* gimple-ssa-warn-access.cc (maybe_warn_for_bound): Tighten up
	the phrasing of a warning.
	(check_access): Use the remaining size after subtracting any offset
	rather than the whole object size.
	* pointer-query.cc (access_ref::get_ref): Clear BASE0 flag if it's
	clear for any nonnull PHI argument.
	(compute_objsize): Clear argument.

gcc/testsuite/ChangeLog:

	PR middle-end/101600
	PR middle-end/101977
	* g++.dg/pr100574.C: Prune out valid warning.
	* gcc.dg/pr20126.c: Same.
	* gcc.dg/Wstringop-overread.c: Adjust text of expected warnings.
	Add new instances.
	* gcc.dg/warn-strnlen-no-nul.c: Same.
	* g++.dg/warn/Warray-bounds-26.C: New test.
	* gcc.dg/Warray-bounds-88.c: New test.
---
 gcc/gimple-ssa-warn-access.cc | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

(limited to 'gcc/gimple-ssa-warn-access.cc')

diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
index 4a2dd9a..5df97a6 100644
--- a/gcc/gimple-ssa-warn-access.cc
+++ b/gcc/gimple-ssa-warn-access.cc
@@ -704,6 +704,15 @@ maybe_warn_for_bound (opt_code opt, location_t loc, GimpleOrTree exp, tree func,
   if (opt == OPT_Wstringop_overread)
     {
       bool maybe = pad && pad->src.phi ();
+      if (maybe)
+	{
+	  /* Issue a "maybe" warning only if the PHI refers to objects
+	     at least one of which has more space remaining than the bound.
+	     Otherwise, if the bound is greater, use the definitive form.  */
+	  offset_int remmax = pad->src.size_remaining ();
+	  if (remmax < wi::to_offset (bndrng[0]))
+	    maybe = false;
+	}
 
       if (tree_int_cst_lt (maxobjsize, bndrng[0]))
 	{
@@ -788,6 +797,15 @@ maybe_warn_for_bound (opt_code opt, location_t loc, GimpleOrTree exp, tree func,
     }
 
   bool maybe = pad && pad->dst.phi ();
+  if (maybe)
+    {
+      /* Issue a "maybe" warning only if the PHI refers to objects
+	 at least one of which has more space remaining than the bound.
+	 Otherwise, if the bound is greater, use the definitive form.  */
+      offset_int remmax = pad->dst.size_remaining ();
+      if (remmax < wi::to_offset (bndrng[0]))
+	maybe = false;
+    }
   if (tree_int_cst_lt (maxobjsize, bndrng[0]))
     {
       if (bndrng[0] == bndrng[1])
@@ -1418,7 +1436,7 @@ check_access (GimpleOrTree exp, tree dstwrite,
       location_t loc = get_location (exp);
       tree size = dstsize;
       if (pad && pad->mode == access_read_only)
-	size = wide_int_to_tree (sizetype, pad->src.sizrng[1]);
+	size = wide_int_to_tree (sizetype, pad->src.size_remaining ());
 
       if (range[0] && maxread && tree_fits_uhwi_p (size))
 	{
-- 
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