On Tue, 2012-01-10 at 14:53 +0100, Richard Guenther wrote:
> On Tue, Jan 10, 2012 at 2:43 PM, William J. Schmidt
> <wschm...@linux.vnet.ibm.com> wrote:
> > Greetings,
> >
> > This patch follows Richard Guenther's suggestion of 2011-07-05 in
> > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49642 to fix the problem in
> > gcc 4.6. It prevents choosing a function split point that is dominated
> > by a builtin call to __builtin_constant_p.
> >
> > The bug was marked fixed in 4.7 since the extra FRE pass allows the
> > correct optimization to be done even in the presence of
> > __builtin_constant_p. However, 4.7 still fails in the presence of
> > -fno-tree-fre. I think we should probably include a variation of this
> > patch in 4.7 that only kicks in when FRE has been disabled at the
> > command line. The test case would also be modified slightly to include
> > -fno-tree-fre in the dg-compile statement. Thoughts?
>
> I think it should be unconditionally restrict splitting (I suppose on the
> trunk the __builtin_constant_p is optimized away already).
OK. Yes, on trunk it is optimized away (when FRE is not disabled).
Having the logic unconditional is fine with me; I'd like to use
-fno-tree-fre in the test case so it actually gets tested, though. Or
have two variants, one with, one without.
>
> Btw, this will also disqualify any point below
>
> if (__builtin_constant_p (...))
> {
> ...
> }
>
> because after the if join all BBs are dominated by the __builtin_constant_p
> call. What we want to disallow is splitting at a block that is dominated
> by the true edge of the condition fed by the __builtin_constant_p result ...
True. What we have is:
D.1899_68 = __builtin_constant_p (D.1898_67);
if (D.1899_68 != 0)
goto <bb 3>;
else
goto <bb 133>;
So I suppose we have to walk the immediate uses of the LHS of the call,
find all that are part of a condition, and mark the target block for
nonzero (in this case <bb 3>) as a forbidden dominator. I can tighten
this up.
>
> Honza?
>
> > The 4.6 patch was bootstrapped and tests cleanly on powerpc64-linux-gnu.
> > OK for 4.6 branch?
> >
> > Thanks,
> > Bill
> >
> >
> > gcc:
> >
> > 2012-01-10 Bill Schmidt <wschm...@linux.vnet.ibm.com>
> >
> > PR tree-optimization/49642
> > * ipa-split.c (forbidden_dominators): New variable.
> > (check_forbidden_calls): New function.
> > (dominated_by_forbidden): Likewise.
> > (consider_split): Check for forbidden calls.
> > (execute_split_functions): Initialize and free forbidden
> > dominators info; call check_forbidden_calls.
> >
> > gcc/testsuite:
> >
> > 2012-01-10 Bill Schmidt <wschm...@linux.vnet.ibm.com>
> >
> > PR tree-optimization/49642
> > * gcc.dg/tree-ssa/pr49642.c: New test.
> >
> >
> > Index: gcc/testsuite/gcc.dg/tree-ssa/pr49642.c
> > ===================================================================
> > --- gcc/testsuite/gcc.dg/tree-ssa/pr49642.c (revision 0)
> > +++ gcc/testsuite/gcc.dg/tree-ssa/pr49642.c (revision 0)
> > @@ -0,0 +1,49 @@
> > +/* Verify that ipa-split is disabled following __builtin_constant_p. */
> > +
> > +/* { dg-do compile } */
> > +/* { dg-options "-O2 -fdump-tree-optimized" } */
> > +
> > +typedef unsigned int u32;
> > +typedef unsigned long long u64;
> > +
> > +static inline __attribute__((always_inline)) __attribute__((const))
> > +int __ilog2_u32(u32 n)
> > +{
> > + int bit;
> > + asm ("cntlzw %0,%1" : "=r" (bit) : "r" (n));
> > + return 31 - bit;
> > +}
> > +
> > +
> > +static inline __attribute__((always_inline)) __attribute__((const))
> > +int __ilog2_u64(u64 n)
> > +{
> > + int bit;
> > + asm ("cntlzd %0,%1" : "=r" (bit) : "r" (n));
> > + return 63 - bit;
> > +}
> > +
> > +
> > +
> > +static u64 ehca_map_vaddr(void *caddr);
> > +
> > +struct ehca_shca {
> > + u32 hca_cap_mr_pgsize;
> > +};
> > +
> > +static u64 ehca_get_max_hwpage_size(struct ehca_shca *shca)
> > +{
> > + return 1UL << ( __builtin_constant_p(shca->hca_cap_mr_pgsize) ? (
> > (shca->hca_cap_mr_pgsize) < 1 ? ____ilog2_NaN() : (shca->hca_cap_mr_pgsize)
> > & (1ULL << 63) ? 63 : (shca->hca_cap_mr_pgsize) & (1ULL << 62) ? 62 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 61) ? 61 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 60) ? 60 : (shca->hca_cap_mr_pgsize) & (1ULL << 59) ? 59 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 58) ? 58 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 57) ? 57 : (shca->hca_cap_mr_pgsize) & (1ULL << 56) ? 56 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 55) ? 55 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 54) ? 54 : (shca->hca_cap_mr_pgsize) & (1ULL << 53) ? 53 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 52) ? 52 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 51) ? 51 : (shca->hca_cap_mr_pgsize) & (1ULL << 50) ? 50 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 49) ? 49 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 48) ? 48 : (shca->hca_cap_mr_pgsize) & (1ULL << 47) ? 47 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 46) ? 46 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 45) ? 45 : (shca->hca_cap_mr_pgsize) & (1ULL << 44) ? 44 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 43) ? 43 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 42) ? 42 : (shca->hca_cap_mr_pgsize) & (1ULL << 41) ? 41 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 40) ? 40 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 39) ? 39 : (shca->hca_cap_mr_pgsize) & (1ULL << 38) ? 38 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 37) ? 37 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 36) ? 36 : (shca->hca_cap_mr_pgsize) & (1ULL << 35) ? 35 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 34) ? 34 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 33) ? 33 : (shca->hca_cap_mr_pgsize) & (1ULL << 32) ? 32 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 31) ? 31 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 30) ? 30 : (shca->hca_cap_mr_pgsize) & (1ULL << 29) ? 29 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 28) ? 28 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 27) ? 27 : (shca->hca_cap_mr_pgsize) & (1ULL << 26) ? 26 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 25) ? 25 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 24) ? 24 : (shca->hca_cap_mr_pgsize) & (1ULL << 23) ? 23 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 22) ? 22 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 21) ? 21 : (shca->hca_cap_mr_pgsize) & (1ULL << 20) ? 20 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 19) ? 19 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 18) ? 18 : (shca->hca_cap_mr_pgsize) & (1ULL << 17) ? 17 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 16) ? 16 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 15) ? 15 : (shca->hca_cap_mr_pgsize) & (1ULL << 14) ? 14 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 13) ? 13 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 12) ? 12 : (shca->hca_cap_mr_pgsize) & (1ULL << 11) ? 11 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 10) ? 10 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 9) ? 9 : (shca->hca_cap_mr_pgsize) & (1ULL << 8) ? 8 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 7) ? 7 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 6) ? 6 : (shca->hca_cap_mr_pgsize) & (1ULL << 5) ? 5 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 4) ? 4 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 3) ? 3 : (shca->hca_cap_mr_pgsize) & (1ULL << 2) ? 2 :
> > (shca->hca_cap_mr_pgsize) & (1ULL << 1) ? 1 : (shca->hca_cap_mr_pgsize) &
> > (1ULL << 0) ? 0 : ____ilog2_NaN() ) : (sizeof(shca->hca_cap_mr_pgsize) <=
> > 4) ? __ilog2_u32(shca->hca_cap_mr_pgsize) :
> > __ilog2_u64(shca->hca_cap_mr_pgsize) );
> > +}
> > +
> > +int x(struct ehca_shca *shca) {
> > + return ehca_get_max_hwpage_size(shca);
> > +}
> > +
> > +int y(struct ehca_shca *shca)
> > +{
> > + return ehca_get_max_hwpage_size(shca);
> > +}
> > +
> > +/* { dg-final { scan-tree-dump-times "____ilog2_NaN" 0 "optimized" } } */
> > +/* { dg-final { cleanup-tree-dump "optimized" } } */
> > Index: gcc/ipa-split.c
> > ===================================================================
> > --- gcc/ipa-split.c (revision 183033)
> > +++ gcc/ipa-split.c (working copy)
> > @@ -130,6 +130,10 @@ struct split_point
> >
> > struct split_point best_split_point;
> >
> > +/* Set of basic blocks that are not allowed to dominate a split point. */
> > +
> > +bitmap forbidden_dominators;
> > +
> > static tree find_retval (basic_block return_bb);
> >
> > /* Callback for walk_stmt_load_store_addr_ops. If T is non-SSA automatic
> > @@ -270,6 +274,49 @@ done:
> > return ok;
> > }
> >
> > +/* If STMT is a call, check the callee against a list of forbidden
> > + functions. If a match is found, set the bit for block BB in the
> > + forbidden dominators bitmap. The purpose of this is to avoid
> > + selecting a split point where we are likely to lose the chance
> > + to optimize away an unused function call. */
> > +
> > +static void
> > +check_forbidden_calls (gimple stmt, basic_block bb)
> > +{
> > + tree fndecl;
> > +
> > + if (!is_gimple_call (stmt))
> > + return;
> > +
> > + fndecl = gimple_call_fndecl (stmt);
> > +
> > + if (fndecl
> > + && TREE_CODE (fndecl) == FUNCTION_DECL
> > + && DECL_BUILT_IN (fndecl)
> > + /* At the moment, __builtin_constant_p is the only forbidden
> > + function call (see PR49642). */
> > + && DECL_FUNCTION_CODE (fndecl) == BUILT_IN_CONSTANT_P)
> > + bitmap_set_bit (forbidden_dominators, bb->index);
> > +}
> > +
> > +/* If BB is dominated by any block in the forbidden dominators set,
> > + return TRUE; else FALSE. */
> > +
> > +static bool
> > +dominated_by_forbidden (basic_block bb)
> > +{
> > + unsigned dom_bb;
> > + bitmap_iterator bi;
> > +
> > + EXECUTE_IF_SET_IN_BITMAP (forbidden_dominators, 1, dom_bb, bi)
> > + {
> > + if (dominated_by_p (CDI_DOMINATORS, bb, BASIC_BLOCK (dom_bb)))
> > + return true;
> > + }
> > +
> > + return false;
> > +}
> > +
> > /* We found an split_point CURRENT. NON_SSA_VARS is bitmap of all non ssa
> > variables used and RETURN_BB is return basic block.
> > See if we can split function here. */
> > @@ -411,6 +458,18 @@ consider_split (struct split_point *current, bitma
> > " Refused: split part has non-ssa uses\n");
> > return;
> > }
> > +
> > + /* If the split point is dominated by a forbidden function call,
> > + reject the split. */
> > + if (!bitmap_empty_p (forbidden_dominators)
> > + && dominated_by_forbidden (current->entry_bb))
> > + {
> > + if (dump_file && (dump_flags & TDF_DETAILS))
> > + fprintf (dump_file,
> > + " Refused: split point dominated by forbidden call\n");
> > + return;
> > + }
> > +
> > /* See if retval used by return bb is computed by header or split part.
> > When it is computed by split part, we need to produce return statement
> > in the split part and add code to header to pass it around.
> > @@ -1329,6 +1388,10 @@ execute_split_functions (void)
> > return 0;
> > }
> >
> > + /* Initialize bitmap to track forbidden calls. */
> > + forbidden_dominators = BITMAP_ALLOC (NULL);
> > + calculate_dominance_info (CDI_DOMINATORS);
> > +
> > /* Compute local info about basic blocks and determine function
> > size/time. */
> > VEC_safe_grow_cleared (bb_info, heap, bb_info_vec, last_basic_block + 1);
> > memset (&best_split_point, 0, sizeof (best_split_point));
> > @@ -1350,6 +1413,7 @@ execute_split_functions (void)
> > this_time = estimate_num_insns (stmt, &eni_time_weights) * freq;
> > size += this_size;
> > time += this_time;
> > + check_forbidden_calls (stmt, bb);
> >
> > if (dump_file && (dump_flags & TDF_DETAILS))
> > {
> > @@ -1371,6 +1435,7 @@ execute_split_functions (void)
> > BITMAP_FREE (best_split_point.split_bbs);
> > todo = TODO_update_ssa | TODO_cleanup_cfg;
> > }
> > + BITMAP_FREE (forbidden_dominators);
> > VEC_free (bb_info, heap, bb_info_vec);
> > bb_info_vec = NULL;
> > return todo;
> >
> >
> >
>
