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Re: [asan] Emit GIMPLE directly, small cleanups


On Thu, Oct 11, 2012 at 01:14:31PM -0400, Diego Novillo wrote:
> On 2012-10-11 12:38 , Jakub Jelinek wrote:
> 
> >-  gimple_seq seq, stmts;
> >-  tree shadow_type = size_in_bytes == 16 ?
> >-      short_integer_type_node : char_type_node;
> >-  tree shadow_ptr_type = build_pointer_type (shadow_type);
> >-  tree uintptr_type = lang_hooks.types.type_for_mode (ptr_mode,
> >-                                                      /*unsignedp=*/true);
> >+  tree shadow_ptr_type = shadow_ptr_types[size_in_bytes == 16];
> 
> Add '? 1 : 0' in the array index expression.

Ok.

> >    /* Build
> >-     (base_addr >> ASAN_SHADOW_SHIFT) | targetm.asan_shadow_offset ().  */
> >+     (base_addr >> ASAN_SHADOW_SHIFT) + targetm.asan_shadow_offset ().  */
> 
> Hm, I wonder if this is a documentation problem or we're generating
> bad runtime code.  Wei, you tested the runtime and it was working
> with the GCC generated code, right?

The asan web pages document |, the old tree-asan.c emitted +, I've changed
it to BIT_IOR_EXPR, but that resulted in worse assembly, and I believe at
least for the current x86_64 and i686 address ranges and shadow offset
values it actually doesn't matter.
On x86_64 stack is like 0x7ffff6e00000, shifted down by 3 is still smaller
than 1L << 44 that is ored or added to it.  And the negative half of the
address space is used by the kernel, nothing is mapped into it (besides
vsyscall page) and neither | nor + of 1L << 44 to it would work well.
On i386, | and + works the same for all addresses, as 0xffffffffU >> 3
is still smaller than 1 << 29.
The reason why + generates better code on x86_64/i686 is that one can use
e.g. movzbl (%r1, %r2), %r3 instead of orq %r2, %r1; movzb (%r1), %r3.

> >+  if (shadow_ptr_types[0] == NULL_TREE)
> >+    {
> >+      alias_set_type set = new_alias_set ();
> >+      shadow_ptr_types[0]
> >+	= build_distinct_type_copy (unsigned_char_type_node);
> >+      TYPE_ALIAS_SET (shadow_ptr_types[0]) = set;
> >+      shadow_ptr_types[0] = build_pointer_type (shadow_ptr_types[0]);
> >+      shadow_ptr_types[1]
> >+	= build_distinct_type_copy (short_unsigned_type_node);
> >+      TYPE_ALIAS_SET (shadow_ptr_types[1]) = set;
> >+      shadow_ptr_types[1] = build_pointer_type (shadow_ptr_types[1]);
> >+    }
> 
> Move this to an initialization function, please.

Okay.

	Jakub


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