From: Martin Uecker <uecker@tugraz.at>
Date: Sat, 30 May 2026 14:30:50 +0000 (+0200)
Subject: c: fix false positive for -Wvla-parameter [PR98539]
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=dcd83c656ef1c00d5b5a70deb7ba608e68a8aea4;p=thirdparty%2Fgcc.git

c: fix false positive for -Wvla-parameter [PR98539]

In case of VLAs that are multi-dimensional arrays with unspecified sizes,
the test in the warning code did not work correctly.  Fix this by
explicitely checking that there are specified or unspecified size
expressions to determine the presence of a VLA.

	PR c/98539

gcc/c-family/ChangeLog:
	* c-warn.cc (warn_parm_array_mismatch): Check number of size
	expressions.

gcc/testsuite/ChangeLog:
	* gcc.dg/pr98539.c: New test.
---

diff --git a/gcc/c-family/c-warn.cc b/gcc/c-family/c-warn.cc
index 07d15c0b09c..1767d2dc090 100644
--- a/gcc/c-family/c-warn.cc
+++ b/gcc/c-family/c-warn.cc
@@ -3479,9 +3479,28 @@ warn_parm_array_mismatch (location_t origloc, rdwr_map *cur_idx,
       cura->ptrarg = parmpos;
     }
 
+
+  unsigned newbnds = 0;
+  unsigned newunspec = 0;
+
+  if (newa->internal_p)
+    {
+      newbnds = newa->vla_bounds (&newunspec);
+      newbnds += newunspec;
+    }
+
+  unsigned curbnds = 0;
+  unsigned curunspec = 0;
+
+  if (cura->internal_p)
+    {
+      curbnds = cura->vla_bounds (&curunspec);
+      curbnds += curunspec;
+    }
+
   /* Set if the parameter is [re]declared as a VLA.  */
-  const bool cur_vla_p = cura->size || cura->minsize == HOST_WIDE_INT_M1U;
-  const bool new_vla_p = newa->size || newa->minsize == HOST_WIDE_INT_M1U;
+  const bool cur_vla_p = cura->minsize == HOST_WIDE_INT_M1U || 0 < curbnds;
+  const bool new_vla_p = newa->minsize == HOST_WIDE_INT_M1U || 0 < newbnds;
 
   if (DECL_P (curp))
     origloc = DECL_SOURCE_LOCATION (curp);
@@ -3560,10 +3579,6 @@ warn_parm_array_mismatch (location_t origloc, rdwr_map *cur_idx,
 
   if (newa->size || cura->size)
     {
-      unsigned newunspec, curunspec;
-      unsigned newbnds = newa->vla_bounds (&newunspec) + newunspec;
-      unsigned curbnds = cura->vla_bounds (&curunspec) + curunspec;
-
       if (newbnds != curbnds)
 	{
 	  if (warning_n (newloc, OPT_Wvla_parameter, newbnds,
diff --git a/gcc/testsuite/gcc.dg/pr98539.c b/gcc/testsuite/gcc.dg/pr98539.c
new file mode 100644
index 00000000000..32e118dd10a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr98539.c
@@ -0,0 +1,6 @@
+/* { dg-do compile } */
+/* { dg-options "-std=c99 -Wvla-parameter" } */
+
+void foo(int n, double x[3][*]);
+void foo(int n, double x[3][n]) { }
+