Am Dienstag, den 04.02.2020, 15:01 +0100 schrieb Richard Biener:
> On Sat, Feb 1, 2020 at 1:04 AM Uecker, Martin
> <martin.uec...@med.uni-goettingen.de> wrote:
> >
> >
> >
> > Hi Richard and Joseph,
> >
> > for discussion: here is my simple patch
> > for __builtin_escape/__builtin_bless.
> >
> > Maybe it does something stupid.
>
> I'd use an internal function once the frontend inserts the calls,
> we shouldn't expose those to the user.
Ok. I thought it might be useful for testing...
> I expect the builtins to show as quite invasive with their
> data dependence blocking many optimizations.
Yes, I wondering about the impact of this on
optimization and whether this could be made
more light-weight somehow.
Do you think it is worth investigating
the use of some other kind of marker?
> Any reason that __builtin_escape is not marked as const?
Conceptually, letting something escape (or marking
it "exposed" according to the formal semantics
in the PVNI proposal) is a side-effect.
Practically, if I mark it constant, I think the
problem was that it was getting optimized away
completely.
> Do you try to prevent code motion of it so flow-sensitive
> "escape" analysis can be used?
If I don't miss something important, there is
no flow-sensitive analysis done in GCC.
> But nothing prevents hoisting of the bless call
> across the escape one.
With flow-sensitive analysis, this would be
incorrect.
Martin
> >
> > diff --git a/gcc/builtins.c b/gcc/builtins.c
> > index e4a8694054e..d0046135213 100644
> > --- a/gcc/builtins.c
> > +++ b/gcc/builtins.c
> > @@ -6014,6 +6014,31 @@ expand_builtin_unreachable (void)
> > emit_barrier ();
> > }
> >
> > +
> > +static rtx
> > +expand_builtin_escape (tree exp, rtx target)
> > +{
> > + if (call_expr_nargs (exp) < 1)
> > + return const0_rtx;
> > +
> > + target = expand_expr (CALL_EXPR_ARG (exp, 0), target, Pmode,
> > + EXPAND_NORMAL);
> > +
> > + return target;
> > +}
> > +
> > +static rtx
> > +expand_builtin_bless (tree exp, rtx target)
> > +{
> > + if (call_expr_nargs (exp) < 1)
> > + return const0_rtx;
> > +
> > + target = expand_expr (CALL_EXPR_ARG (exp, 0), target, Pmode,
> > + EXPAND_NORMAL);
> > +
> > + return target;
> > +}
> > +
> > /* Expand EXP, a call to fabs, fabsf or fabsl.
> > Return NULL_RTX if a normal call should be emitted rather than
> > expanding
> > the function inline. If convenient, the result should be
> > placed
> > @@ -8304,6 +8329,12 @@ expand_builtin (tree exp, rtx target, rtx
> > subtarget, machine_mode mode,
> > expand_builtin_unreachable ();
> > return const0_rtx;
> >
> > + case BUILT_IN_ESCAPE:
> > + return expand_builtin_escape (exp, target);
> > +
> > + case BUILT_IN_BLESS:
> > + return expand_builtin_bless (exp, target);
> > +
> > CASE_FLT_FN (BUILT_IN_SIGNBIT):
> > case BUILT_IN_SIGNBITD32:
> > case BUILT_IN_SIGNBITD64:
> > diff --git a/gcc/builtins.def b/gcc/builtins.def
> > index fa8b0641ab1..9264a0fdaab 100644
> > --- a/gcc/builtins.def
> > +++ b/gcc/builtins.def
> > @@ -865,6 +865,8 @@ DEF_EXT_LIB_BUILTIN (BUILT_IN_EXECVP,
> > "execvp", BT_FN_INT_CONST_STRING_PT
> > DEF_EXT_LIB_BUILTIN (BUILT_IN_EXECVE, "execve",
> > BT_FN_INT_CONST_STRING_PTR_CONST_STRING_PTR_CONST_STRING,
> > ATTR_NOTHROW_LIST)
> > DEF_LIB_BUILTIN (BUILT_IN_EXIT, "exit", BT_FN_VOID_INT,
> > ATTR_NORETURN_NOTHROW_LIST)
> > DEF_GCC_BUILTIN (BUILT_IN_EXPECT, "expect",
> > BT_FN_LONG_LONG_LONG, ATTR_CONST_NOTHROW_LEAF_LIST)
> > +DEF_GCC_BUILTIN (BUILT_IN_ESCAPE, "escape", BT_FN_PTR_PTR,
> > ATTR_NOTHROW_LEAF_LIST)
> > +DEF_GCC_BUILTIN (BUILT_IN_BLESS, "bless", BT_FN_PTR_PTR,
> > ATTR_CONST_NOTHROW_LEAF_LIST)
> > DEF_GCC_BUILTIN (BUILT_IN_EXPECT_WITH_PROBABILITY,
> > "expect_with_probability", BT_FN_LONG_LONG_LONG_DOUBLE,
> > ATTR_CONST_NOTHROW_LEAF_LIST)
> > DEF_GCC_BUILTIN (BUILT_IN_ASSUME_ALIGNED, "assume_aligned",
> > BT_FN_PTR_CONST_PTR_SIZE_VAR, ATTR_CONST_NOTHROW_LEAF_LIST)
> > DEF_GCC_BUILTIN (BUILT_IN_EXTEND_POINTER, "extend_pointer",
> > BT_FN_UNWINDWORD_PTR, ATTR_CONST_NOTHROW_LEAF_LIST)
> > diff --git a/gcc/testsuite/gcc.dg/alias-17.c
> > b/gcc/testsuite/gcc.dg/alias-17.c
> > new file mode 100644
> > index 00000000000..c375e4027ca
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/alias-17.c
> > @@ -0,0 +1,29 @@
> > +/* { dg-do run } */
> > +/* { dg-options "-O1" } */
> > +
> > +
> > +static
> > +int test(int a, int b, int c)
> > +{
> > + int x, y;
> > + int d = (&x < &y) ? 1 : -1;
> > + if (a) __builtin_escape(&y);
> > + y = 0; //!
> > + int *q = &x;
> > + q += d;
> > + int *r = q;
> > + if (b) r = __builtin_bless(q);
> > + *(c ? r : q) = 1;
> > + return y;
> > +}
> > +
> > +int main()
> > +{
> > + if (0 != test(0, 0, 1)) __builtin_abort();
> > + if (0 != test(0, 1, 0)) __builtin_abort();
> > + if (0 != test(0, 1, 1)) __builtin_abort();
> > + if (0 != test(1, 0, 1)) __builtin_abort();
> > +// if (0 != test(1, 1, 0)) __builtin_abort();
> > + if (0 == test(1, 1, 1)) __builtin_abort();
> > + return 0;
> > +}
> > diff --git a/gcc/tree-ssa-alias.c b/gcc/tree-ssa-alias.c
> > index 670676f20c3..d5befff71a6 100644
> > --- a/gcc/tree-ssa-alias.c
> > +++ b/gcc/tree-ssa-alias.c
> > @@ -2462,6 +2462,8 @@ ref_maybe_used_by_call_p_1 (gcall *call,
> > ao_ref *ref, bool tbaa_p)
> > }
> >
> > /* The following builtins do not read from memory. */
> > + case BUILT_IN_ESCAPE:
> > + case BUILT_IN_BLESS:
> > case BUILT_IN_FREE:
> > case BUILT_IN_MALLOC:
> > case BUILT_IN_POSIX_MEMALIGN:
> > diff --git a/gcc/tree-ssa-ccp.c b/gcc/tree-ssa-ccp.c
> > index be6647db894..53a38a04ebb 100644
> > --- a/gcc/tree-ssa-ccp.c
> > +++ b/gcc/tree-ssa-ccp.c
> > @@ -1963,6 +1963,8 @@ evaluate_stmt (gimple *stmt)
> > break;
> >
> > /* These builtins return their first argument,
> > unmodified. */
> > + case BUILT_IN_ESCAPE:
> > + case BUILT_IN_BLESS:
> > case BUILT_IN_MEMCPY:
> > case BUILT_IN_MEMMOVE:
> > case BUILT_IN_MEMSET:
> > diff --git a/gcc/tree-ssa-structalias.c b/gcc/tree-ssa-
> > structalias.c
> > index 416a26c996c..003349c7278 100644
> > --- a/gcc/tree-ssa-structalias.c
> > +++ b/gcc/tree-ssa-structalias.c
> > @@ -4381,6 +4381,24 @@ find_func_aliases_for_builtin_call (struct
> > function *fn, gcall *t)
> > in the alias-oracle query functions explicitly! */
> > switch (DECL_FUNCTION_CODE (fndecl))
> > {
> > + case BUILT_IN_ESCAPE:
> > + {
> > + make_escape_constraint (gimple_call_arg (t, 0));
> > + return true;
> > + }
> > + case BUILT_IN_BLESS:
> > + {
> > + tree lhs = gimple_call_lhs (t);
> > + struct constraint_expr rhsc, *lhsp;
> > + unsigned j;
> > + get_constraint_for (lhs, &lhsc);
> > + rhsc.var = nonlocal_id;
> > + rhsc.offset = 0;
> > + rhsc.type = SCALAR;
> > + FOR_EACH_VEC_ELT (lhsc, j, lhsp)
> > + process_constraint (new_constraint (*lhsp, rhsc));
> > + return true;
> > + }
> > /* All the following functions return a pointer to the same
> > object
> > as their first argument points to. The functions do not
> > add
> > to the ESCAPED solution. The functions make the first
> > argument
> > @@ -5257,6 +5275,7 @@ find_func_clobbers (struct function *fn,
> > gimple *origt)
> > if (gimple_call_builtin_p (t, BUILT_IN_NORMAL))
> > switch (DECL_FUNCTION_CODE (decl))
> > {
> > +
> > /* The following functions use and clobber memory pointed
> > to
> > by their arguments. */
> > case BUILT_IN_STRCPY:
> > @@ -5349,6 +5368,9 @@ find_func_clobbers (struct function *fn,
> > gimple *origt)
> > case BUILT_IN_ASSUME_ALIGNED:
> > case BUILT_IN_FREE:
> > return;
> > + case BUILT_IN_ESCAPE:
> > + case BUILT_IN_BLESS:
> > + return;
> > /* Trampolines are of no interest to us. */
> > case BUILT_IN_INIT_TRAMPOLINE:
> > case BUILT_IN_ADJUST_TRAMPOLINE:
