diagnose bogus assume_aligned attributes (PR 87533)

PR middle-end/87533 - bogus assume_aligned attribute silently accepted

gcc/c-family/ChangeLog:

	PR middle-end/87533
	* c-attribs.c (handle_assume_aligned_attribute): Diagnose and
	reject invalid attribute specifications.

gcc/testsuite/ChangeLog:

	PR middle-end/87533
	* gcc.dg/attr-assume_aligned-4.c: New test.

Index: gcc/c-family/c-attribs.c
===================================================================
@@ -2451,23 +2454,63 @@  static tree
    struct attribute_spec.handler.  */
 
 static tree
-handle_assume_aligned_attribute (tree *, tree, tree args, int,
+handle_assume_aligned_attribute (tree *node, tree name, tree args, int,
 				 bool *no_add_attrs)
 {
+  tree decl = *node;
+  tree rettype = TREE_TYPE (decl);
+  if (TREE_CODE (rettype) != POINTER_TYPE)
+    {
+      warning (OPT_Wattributes,
+	       "%qE attribute ignored on a function returning %qT",
+	       name, rettype);
+      *no_add_attrs = true;
+      return NULL_TREE;
+    }
+
+  /* The alignment specified by the first argument.  */
+  tree align = NULL_TREE;
+
   for (; args; args = TREE_CHAIN (args))
     {
-      tree position = TREE_VALUE (args);
-      if (position && TREE_CODE (position) != IDENTIFIER_NODE
-	  && TREE_CODE (position) != FUNCTION_DECL)
-	position = default_conversion (position);
+      tree val = TREE_VALUE (args);
+      if (val && TREE_CODE (val) != IDENTIFIER_NODE
+	  && TREE_CODE (val) != FUNCTION_DECL)
+	val = default_conversion (val);
 
-      if (TREE_CODE (position) != INTEGER_CST)
+      if (!tree_fits_shwi_p (val))
 	{
 	  warning (OPT_Wattributes,
-		   "assume_aligned parameter not integer constant");
+		   "%qE attribute argument %E is not an integer constant",
+		   name, val);
 	  *no_add_attrs = true;
 	  return NULL_TREE;
 	}
+
+      if (!align)
+	{
+	  /* Validate and save the alignment.  */
+	  if (!integer_pow2p (val))
+	    {
+	      warning (OPT_Wattributes,
+		       "%qE attribute argument %E is not a power of 2",
+		       name, val);
+	      *no_add_attrs = true;
+	      return NULL_TREE;
+	}
+
+	  align = val;
+	}
+      else if (tree_int_cst_sgn (val) < 0 || tree_int_cst_le (align, val))
+	{
+	  /* The misalignment specified by the second argument
+	     must be non-negative and less than the alignment.  */
+	  warning (OPT_Wattributes,
+		   "%qE attribute argument %E is not in the range [0, %E)",
+		   name, val, align);
+	  *no_add_attrs = true;
+	  return NULL_TREE;
+	}
     }
   return NULL_TREE;
 }
Index: gcc/testsuite/gcc.dg/attr-assume_aligned-4.c
===================================================================
--- gcc/testsuite/gcc.dg/attr-assume_aligned-4.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/attr-assume_aligned-4.c	(working copy)
@@ -0,0 +1,36 @@ 
+/* PR middle-end/87533 - bogus assume_aligned attribute silently accepted
+   { dg-do compile }
+   { dg-options "-Wall" } */
+
+#define A(...)  __attribute__ ((assume_aligned (__VA_ARGS__)))
+
+A (1) void fv_1 (void);       /* { dg-warning ".assume_aligned. attribute ignored on a function returning .void." } */
+
+A (1) int fi_1 (void);        /* { dg-warning ".assume_aligned. attribute ignored on a function returning .int." } */
+
+A (-1) void* fpv_m1 (void);   /* { dg-warning ".assume_aligned. attribute argument -1 is not a power of 2" } */
+
+A (0) void* fpv_0 (void);     /* { dg-warning ".assume_aligned. attribute argument 0 is not a power of 2" } */
+
+/* Alignment of 1 is fine, it just doesn't offer any benefits.  */
+A (1) void* fpv_1 (void);
+
+A (3) void* fpv_3 (void);     /* { dg-warning ".assume_aligned. attribute argument 3 is not a power of 2" } */
+
+A (16383) void* fpv_16km1 (void);     /* { dg-warning ".assume_aligned. attribute argument 16383 is not a power of 2" } */
+A (16384) void* fpv_16k (void);
+A (16385) void* fpv_16kp1 (void);    /* { dg-warning ".assume_aligned. attribute argument 16385 is not a power of 2" } */
+
+A (32767) void* fpv_32km1 (void);     /* { dg-warning ".assume_aligned. attribute argument 32767 is not a power of 2" } */
+
+A (4, -1) void* fpv_4_m1 (void);      /* { dg-warning ".assume_aligned. attribute argument -1 is not in the range \\\[0, 4\\\)" } */
+
+A (4, 0) void* fpv_4_0 (void);
+A (4, 1) void* fpv_4_1 (void);
+A (4, 2) void* fpv_4_2 (void);
+A (4, 3) void* fpv_4_3 (void);
+
+A (4, 4) void* fpv_4_3 (void);        /* { dg-warning ".assume_aligned. attribute argument 4 is not in the range \\\[0, 4\\\)" } */
+
+A (4) void* gpv_4_3 (void);
+A (2) void* gpv_4_3 (void);