On 02/16/2017 03:46 AM, Martin Liška wrote:
On 02/15/2017 05:06 PM, Aldy Hernandez wrote:
On 02/15/2017 09:49 AM, Martin Liška wrote:
Hi.
As mentioned in the PR, gimple nops are wrongly handled in is_maybe_undefined
function.
Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
gimple *def = SSA_NAME_DEF_STMT (t);
+ if (!def || gimple_nop_p (def))
+ return true;
+
Out of curiosity, what is T?
It's a SSA name which belongs to a result_decl:
(gdb) p debug_tree(t)
<ssa_name 0x7fffdaf3b1f8
type <reference_type 0x7ffff122c9d8
type <record_type 0x7ffff0664888 UnicodeString addressable
needs-constructing BLK
size <integer_cst 0x7ffff6892030 constant 512>
unit size <integer_cst 0x7ffff6931c00 constant 64>
align 64 symtab 0 alias set -1 canonical type 0x7ffff66b0e70 fields
<field_decl 0x7ffff0669390 D.165781> context <namespace_decl 0x7ffff66954c0
icu_58>
pointer_to_this <pointer_type 0x7ffff06791f8> reference_to_this <reference_type
0x7fffea593e70> chain <type_decl 0x7ffff0669428 UnicodeString>>
public unsigned DI
size <integer_cst 0x7ffff6876be8 constant 64>
unit size <integer_cst 0x7ffff6876c00 constant 8>
align 64 symtab 0 alias set -1 structural equality>
var <result_decl 0x7fffdaf1f528 resultPattern>
def_stmt GIMPLE_NOP
version 1
ptr-info 0x7fffcc191000>
Because we early bail out if ssa_undefined_value_p() right before calling
SSA_NAME_DEF_STMT, and ssa_undefined_value_p() will already bail if
gimple_nop_p.
So T must be one of:
/* Parameters get their initial value from the function entry. */
else if (TREE_CODE (var) == PARM_DECL)
return false;
/* When returning by reference the return address is actually a hidden
parameter. */
else if (TREE_CODE (var) == RESULT_DECL && DECL_BY_REFERENCE (var))
return false;
This return statement is taken.
/* Hard register variables get their initial value from the ether. */
else if (VAR_P (var) && DECL_HARD_REGISTER (var))
return false;
which I wonder if we should special case in is_maybe_undefined.
Do we need a special case in the function?
It's up to Richi et al, but IMO we should probably treat this as we do
PARM_DECL's, since according to the comment in ssa_undefined_value_p,
returning by reference the return address is actually a hidden
parameter. And as such, we should 'continue' not return in
is_maybe_undefined. This way, we can process the rest of the items in
the worklist.
We already handle:
/* A PARM_DECL will not have an SSA_NAME_DEF_STMT. Parameters
get their initial value from function entry. */
if (SSA_NAME_VAR (t) && TREE_CODE (SSA_NAME_VAR (t)) == PARM_DECL)
continue;
I say we should also handle the rest of the things we handle in
ssa_undefined_value_p:
/* Parameters get their initial value from the function entry. */
else if (TREE_CODE (var) == PARM_DECL)
return false;
/* When returning by reference the return address is actually a hidden
parameter. */
else if (TREE_CODE (var) == RESULT_DECL && DECL_BY_REFERENCE (var))
return false;
/* Hard register variables get their initial value from the ether. */
else if (VAR_P (var) && DECL_HARD_REGISTER (var))
return false;
...all doing a "continue", as opposed to a return.
And if we're going to duplicate all that code, might as well abstract it
out to an inline function.
Also, we should probably still gracefully handle an empty
SSA_NAME_DEF_STMT as you do in your patch, but with a continue as well.
Richi, do you agree?
Aldy
