On Mon, Jan 25, 2016 at 4:40 AM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Fri, Jan 22, 2016 at 7:55 PM, H.J. Lu <hongjiu...@intel.com> wrote:
>> Without the fix for PR 65656, g++ miscompiles __builtin_constant_p in
>> wi::lrshift in wide-int.h. Add a check with PR 65656 testcase to verify
>> that C++ __builtin_constant_p works properly.
>>
>> Tested on x86-64 with working GCC:
>>
>> gcc/auto-host.h:/* #undef HAVE_WORKING_CXX_BUILTIN_CONSTANT_P */
>> prev-gcc/auto-host.h:/* #undef HAVE_WORKING_CXX_BUILTIN_CONSTANT_P */
>> stage1-gcc/auto-host.h:#define HAVE_WORKING_CXX_BUILTIN_CONSTANT_P 1
>>
>> and broken GCC:
>>
>> gcc/auto-host.h:/* #undef HAVE_WORKING_CXX_BUILTIN_CONSTANT_P */
>> prev-gcc/auto-host.h:/* #undef HAVE_WORKING_CXX_BUILTIN_CONSTANT_P */
>> stage1-gcc/auto-host.h:/* #undef HAVE_WORKING_CXX_BUILTIN_CONSTANT_P */
>>
>> Ok for trunk?
>
> I have a hard time seeing how we are "miscompiling"
>
> if (STATIC_CONSTANT_P (xi.precision > HOST_BITS_PER_WIDE_INT)
> ? xi.len == 1 && xi.val[0] >= 0
> : xi.precision <= HOST_BITS_PER_WIDE_INT)
>
> anything that relies on __builtin_constant_p () for sematics is fishy so why
> is this not simply an lrshfit implementation bug?
>
We hit this via:
Breakpoint 1, wi::lrshift<generic_wide_int<fixed_wide_int_storage<192>
>, generic_wide_int<fixed_wide_int_storage<192> > > (x=..., y=...)
at /export/gnu/import/git/sources/gcc-release/gcc/wide-int.h:2898
2898 val[0] = xi.to_uhwi () >> shift;
(gdb) bt
#0 wi::lrshift<generic_wide_int<fixed_wide_int_storage<192> >,
generic_wide_int<fixed_wide_int_storage<192> > > (x=..., y=...)
at /export/gnu/import/git/sources/gcc-release/gcc/wide-int.h:2898
#1 0x00000000009e7bbe in
wi::rshift<generic_wide_int<fixed_wide_int_storage<192> >,
generic_wide_int<fixed_wide_int_storage<192> > > (sgn=<optimized out>,
y=..., x=...)
at /export/gnu/import/git/sources/gcc-release/gcc/wide-int.h:2947
#2 bit_value_binop_1 (code=code@entry=RSHIFT_EXPR,
type=type@entry=0x7fffefe82dc8, val=val@entry=0x7fffffffd7c0,
mask=mask@entry=0x7fffffffd790, r1type=0x7fffefe82dc8, r1val=...,
r1mask=..., r2type=0x7fffefd6b690, r2val=..., r2mask=...)
at /export/gnu/import/git/sources/gcc-release/gcc/tree-ssa-ccp.c:1348
#3 0x00000000009e9e7b in bit_value_binop (code=code@entry=RSHIFT_EXPR,
type=0x7fffefe82dc8, rhs1=rhs1@entry=0x7fffefd71708, rhs2=<optimized out>)
at /export/gnu/import/git/sources/gcc-release/gcc/tree-ssa-ccp.c:1549
#4 0x00000000009eb520 in evaluate_stmt (stmt=stmt@entry=0x7fffefe9a160)
at /export/gnu/import/git/sources/gcc-release/gcc/tree-ssa-ccp.c:1785
#5 0x00000000009ec8d2 in visit_assignment (stmt=stmt@entry=0x7fffefe9a160,
output_p=output_p@entry=0x7fffffffdba0)
at /export/gnu/import/git/sources/gcc-release/gcc/tree-ssa-ccp.c:2258
#6 0x00000000009ec9c2 in ccp_visit_stmt (stmt=0x7fffefe9a160,
taken_edge_p=0x7fffffffdba8, output_p=0x7fffffffdba0)
at /export/gnu/import/git/sources/gcc-release/gcc/tree-ssa-ccp.c:2336
---Type <return> to continue, or q <return> to quit---
#7 0x0000000000a4efcf in simulate_stmt (stmt=stmt@entry=0x7fffefe9a160)
at /export/gnu/import/git/sources/gcc-release/gcc/tree-ssa-propagate.c:348
#8 0x0000000000a50f79 in simulate_block (block=<optimized out>)
at /export/gnu/import/git/sources/gcc-release/gcc/tree-ssa-propagate.c:471
#9 ssa_propagate (
visit_stmt=visit_stmt@entry=0x9ec937 <ccp_visit_stmt(gimple,
edge*, tree*)>, visit_phi=visit_phi@entry=0x9e6aa5
<ccp_visit_phi_node(gphi*)>)
at /export/gnu/import/git/sources/gcc-release/gcc/tree-ssa-propagate.c:888
#10 0x00000000009e6295 in do_ssa_ccp ()
at /export/gnu/import/git/sources/gcc-release/gcc/tree-ssa-ccp.c:2382
#11 (anonymous namespace)::pass_ccp::execute (this=<optimized out>)
at /export/gnu/import/git/sources/gcc-release/gcc/tree-ssa-ccp.c:2415
#12 0x000000000089ca0c in execute_one_pass (pass=pass@entry=0x19b4bf0)
at /export/gnu/import/git/sources/gcc-release/gcc/passes.c:2330
#13 0x000000000089cd62 in execute_pass_list_1 (pass=0x19b4bf0)
at /export/gnu/import/git/sources/gcc-release/gcc/passes.c:2382
#14 0x000000000089cd7f in execute_pass_list_1 (pass=0x19b4a70,
pass@entry=0x19b48f0)
at /export/gnu/import/git/sources/gcc-release/gcc/passes.c:2383
#15 0x000000000089cd9c in execute_pass_list (fn=0x7fffefe98000, pass=0x19b48f0)
at /export/gnu/import/git/sources/gcc-release/gcc/passes.c:2393
#16 0x000000000089ba57 in do_per_function_toporder (
callback=callback@entry=0x89cd83 <execute_pass_list(function*,
opt_pass*)>, ---Type <return> to continue, or q <return> to quit---
data=0x19b48f0) at /export/gnu/import/git/sources/gcc-release/gcc/passes.c:1728
#17 0x000000000089d3e3 in execute_ipa_pass_list (pass=0x19b4890)
at /export/gnu/import/git/sources/gcc-release/gcc/passes.c:2736
#18 0x000000000066f3ac in ipa_passes ()
at /export/gnu/import/git/sources/gcc-release/gcc/cgraphunit.c:2172
#19 symbol_table::compile (this=this@entry=0x7fffefd6b000)
at /export/gnu/import/git/sources/gcc-release/gcc/cgraphunit.c:2313
#20 0x0000000000670be5 in symbol_table::finalize_compilation_unit (
this=0x7fffefd6b000)
at /export/gnu/import/git/sources/gcc-release/gcc/cgraphunit.c:2462
#21 0x000000000058ea41 in c_write_global_declarations ()
at /export/gnu/import/git/sources/gcc-release/gcc/c/c-decl.c:10822
#22 0x0000000000939509 in compile_file ()
at /export/gnu/import/git/sources/gcc-release/gcc/toplev.c:613
#23 0x000000000093b3c4 in do_compile ()
at /export/gnu/import/git/sources/gcc-release/gcc/toplev.c:2067
#24 toplev::main (this=this@entry=0x7fffffffdf60, argc=argc@entry=15,
argv=argv@entry=0x7fffffffe068)
at /export/gnu/import/git/sources/gcc-release/gcc/toplev.c:2165
#25 0x0000000000f50ab7 in main (argc=15, argv=0x7fffffffe068)
at /export/gnu/import/git/sources/gcc-release/gcc/main.c:39
(gdb) p x
$2 = (const generic_wide_int<fixed_wide_int_storage<192> > &)
@0x7fffffffd670: {<fixed_wide_int_storage<192>> = {val = {4294967169,
0, 140737217214936, 92},
len = 1}, static is_sign_extended = <optimized out>}
(gdb) p y
$3 = (const generic_wide_int<fixed_wide_int_storage<192> > &)
@0x7fffffffd640: {<fixed_wide_int_storage<192>> = {val = {64,
824633720833, -4294967168,
140737218308160}, len = 1}, static is_sign_extended = <optimized out>}
(gdb) p xi
$3 = {<wide_int_ref_storage<true>> = {<wi::storage_ref> = {
val = 0x7fffffffcfe0, len = 2, precision = 192}, scratch = {64,
8589921072}}, static is_sign_extended = <optimized out>}
(gdb) p yi
$4 = {<wide_int_ref_storage<true>> = {<wi::storage_ref> = {
val = 0x7fffffffcbc0, len = 1, precision = 192}, scratch = {
140737488344768, 140737488343008}},
static is_sign_extended = <optimized out>}
(gdb)
Somehow PR 65656 miscompiled:
if (STATIC_CONSTANT_P (xi.precision > HOST_BITS_PER_WIDE_INT)
? xi.len == 1 && xi.val[0] >= 0
: xi.precision <= HOST_BITS_PER_WIDE_INT)
which turned the expression into true and hit
val[0] = xi.to_uhwi () >> shift;
result.set_len (1);
--
H.J.
