[gcc(refs/vendors/redhat/heads/gcc-10-branch)] expand: Don't depend on warning flags in code generation of strnlen [PR94189]

[gcc(refs/vendors/redhat/heads/gcc-10-branch)] expand: Don't depend on warning flags in code generation of strnlen [PR94189]

[Jakub Jelinek]

https://gcc.gnu.org/g:7afa3b82918a75a486aad7818f11df9ea7504368

commit 7afa3b82918a75a486aad7818f11df9ea7504368
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Mar 17 10:42:35 2020 +0100

    expand: Don't depend on warning flags in code generation of strnlen [PR94189]
    
    The following testcase FAILs with -O2 -fcompare-debug, but the reason isn't
    that we'd emit different code based on -g or non-debug, but rather that
    we emit different code depending on whether -w is used or not (or e.g.
    -Wno-stringop-overflow or whether some other pass emitted some other warning
    already on the call).
    
    Code generation shouldn't depend on whether we emit a warning or not if at
    all possible.
    
    The following patch punts (i.e. doesn't optimize the strnlen call to a
    constant value) if we would emit the warning if it was enabled.
    In the PR there is an alternate patch which does optimize the strnlen call
    no matter if we emit the warning or not, though I think I prefer the version
    below, e.g. the strnlen call might be crossing field boundaries, which is in
    strict reading undefined, but I'd be afraid people do that in the real
    world programs.
    
    2020-03-17  Jakub Jelinek  <jakub@redhat.com>
    
            PR middle-end/94189
            * builtins.c (expand_builtin_strnlen): Do return NULL_RTX if we would
            emit a warning if it was enabled and don't depend on TREE_NO_WARNING
            for code-generation.
    
            * gcc.dg/pr94189.c: New test.

Diff:
---
 gcc/ChangeLog                  |  7 +++++++
 gcc/builtins.c                 | 22 ++++++++++------------
 gcc/testsuite/ChangeLog        |  5 +++++
 gcc/testsuite/gcc.dg/pr94189.c | 11 +++++++++++
 4 files changed, 33 insertions(+), 12 deletions(-)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 25a27f8070d..fc35ceac272 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2020-03-17  Jakub Jelinek  <jakub@redhat.com>
+
+	PR middle-end/94189
+	* builtins.c (expand_builtin_strnlen): Do return NULL_RTX if we would
+	emit a warning if it was enabled and don't depend on TREE_NO_WARNING
+	for code-generation.
+
 2020-03-16  Vladimir Makarov  <vmakarov@redhat.com>
 
 	PR target/94185
diff --git a/gcc/builtins.c b/gcc/builtins.c
index e4a8694054e..53bae599d3e 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -3142,27 +3142,25 @@ expand_builtin_strnlen (tree exp, rtx target, machine_mode target_mode)
 	    return NULL_RTX;
 	}
 
-      if (lendata.decl
-	  && !TREE_NO_WARNING (exp)
-	  && ((tree_int_cst_lt (len, bound))
-	      || !exact))
+      if (lendata.decl && (tree_int_cst_lt (len, bound) || !exact))
 	{
 	  location_t warnloc
 	    = expansion_point_location_if_in_system_header (loc);
 
-	  if (warning_at (warnloc, OPT_Wstringop_overflow_,
-			  exact
-			  ? G_("%K%qD specified bound %E exceeds the size %E "
-			       "of unterminated array")
-			  : G_("%K%qD specified bound %E may exceed the size "
-			       "of at most %E of unterminated array"),
-			  exp, func, bound, len))
+	  if (!TREE_NO_WARNING (exp)
+	      && warning_at (warnloc, OPT_Wstringop_overflow_,
+			     exact
+			     ? G_("%K%qD specified bound %E exceeds the size "
+				  "%E of unterminated array")
+			     : G_("%K%qD specified bound %E may exceed the "
+				  "size of at most %E of unterminated array"),
+			     exp, func, bound, len))
 	    {
 	      inform (DECL_SOURCE_LOCATION (lendata.decl),
 		      "referenced argument declared here");
 	      TREE_NO_WARNING (exp) = true;
-	      return NULL_RTX;
 	    }
+	  return NULL_RTX;
 	}
 
       if (!len)
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index ac9f0772bcf..879a67d88ef 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-17  Jakub Jelinek  <jakub@redhat.com>
+
+	PR middle-end/94189
+	* gcc.dg/pr94189.c: New test.
+
 2020-03-17  Martin Liska  <mliska@suse.cz>
 
 	PR lto/94157
diff --git a/gcc/testsuite/gcc.dg/pr94189.c b/gcc/testsuite/gcc.dg/pr94189.c
new file mode 100644
index 00000000000..f927d55279a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr94189.c
@@ -0,0 +1,11 @@
+/* PR middle-end/94189 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fcompare-debug" } */
+
+const char a[] = { 'a', 'b', 'c', 'd' };/* { dg-message "declared here" } */
+
+int
+foo (void)
+{
+  return __builtin_strnlen (a, 5);	/* { dg-warning "specified bound 5 exceeds the size 4 of unterminated array" } */
+}