Re: PING: new pass to warn on questionable uses of alloca() and VLAs

[Aldy Hernandez]

On 10/19/2016 09:16 AM, Eric Botcazou wrote:
m68k-suse-linux

visium-elf too.


The attached patch fixes the failures on m68k-suse-linux, visium-elf, 
and arm-eabi.

There were a few problems.

One problem is that on lp64 targets (where sizeof(size_t) != 
sizeof(int)), the warning is slightly different-- and rightly so.  I 
have updated the test to handle both warnings on the respective targets.

The other problem is that the following snippet is incorrectly warning 
on 32-bit targets:

  if (n > 0 && n < 2000)
    p = __builtin_alloca (n);

Looking at the gimple it seems like another case of VRP failing to give 
any range information whatsoever.  I have xfailed it as another case 
where Andrew's upcoming work should theoretically fix this.  The test is 
fine on 64-bit targets.

Can y'all double check it on your respective targets as I only have a 
crude cross build?

Thanks.
Aldy
commit 32b629dcab7b78e8181146338c4b077f1d55a0bf
Author: Aldy Hernandez <al...@redhat.com>
Date:   Wed Oct 19 11:24:44 2016 -0400

        * gcc.dg/Walloca-1.c: Adjust test for !lp64 targets.
        * gcc.dg/Walloca-2.c: Same.

diff --git a/gcc/testsuite/gcc.dg/Walloca-1.c b/gcc/testsuite/gcc.dg/Walloca-1.c
index 34a20c3..32e4ab8 100644
--- a/gcc/testsuite/gcc.dg/Walloca-1.c
+++ b/gcc/testsuite/gcc.dg/Walloca-1.c
@@ -23,7 +23,8 @@ void foo1 (size_t len, size_t len2, size_t len3)
   char *s = alloca (123);
   useit (s);                   // OK, constant argument to alloca
 
-  s = alloca (num);            // { dg-warning "large due to conversion" }
+  s = alloca (num);            // { dg-warning "large due to conversion" "" { 
target lp64 } }
+  // { dg-warning "unbounded use of 'alloca'" "" { target { ! lp64 } } 26 }
   useit (s);
 
   s = alloca(90000);           /* { dg-warning "is too large" } */
diff --git a/gcc/testsuite/gcc.dg/Walloca-2.c b/gcc/testsuite/gcc.dg/Walloca-2.c
index 284b34e..4695fda 100644
--- a/gcc/testsuite/gcc.dg/Walloca-2.c
+++ b/gcc/testsuite/gcc.dg/Walloca-2.c
@@ -8,7 +8,11 @@ g1 (int n)
 {
   void *p;
   if (n > 0 && n < 2000)
-    p = __builtin_alloca (n);
+    // FIXME: This is a bogus warning, and is currently happening on
+    // 32-bit targets because VRP is not giving us any range info for
+    // the argument to __builtin_alloca.  This should be fixed by the
+    // upcoming range work.
+    p = __builtin_alloca (n); // { dg-bogus "unbounded use of 'alloca'" "" { 
xfail { ! lp64 } } }
   else
     p = __builtin_malloc (n);
   f (p);
@@ -31,8 +35,9 @@ g3 (int n)
   void *p;
   if (n > 0 && n < 3000)
     {
-      p = __builtin_alloca (n); // { dg-warning "'alloca' may be too large" }
-      // { dg-message "note:.*argument may be as large as 2999" "note" { 
target *-*-* } 34 }
+      p = __builtin_alloca (n); // { dg-warning "'alloca' may be too large" "" 
{ target lp64} }
+      // { dg-message "note:.*argument may be as large as 2999" "note" { 
target lp64 } 38 }
+      // { dg-warning "unbounded use of 'alloca'" "" { target { ! lp64 } } 38 }
     }
   else
     p = __builtin_malloc (n);