On Sun, Jul 4, 2021 at 8:40 PM apinski--- via Gcc-patches
<[email protected]> wrote:
>
> From: Andrew Pinski <[email protected]>
>
> So the problem here is that replace_phi_edge_with_variable
> will copy range information to a already (not newly) defined
> ssa name. This causes wrong code later on.
That's a bit too conservative I guess? Shouldn't it work for at least
all defs defined in the same block as the original conditional (and
thus then applying to the seq inserted there by the callers)?
I realize it's wrong for, say
_1 = ..
if (_1 != 0)
{
...
if (..)
;
# _2 = PHI <_1, 1>
...
}
with _2 having range [1, +INF] but clearly not _1 at the point of its
definition.
Richard.
> This patch fixes the problem by requiring there to be statements
> that are to be placed before the conditional to be able to
> copy the range info; this assumes the statements will define
> the ssa name.
>
> gcc/ChangeLog:
>
> PR tree-optimization/101256
> * dbgcnt.def (phiopt_edge_range): New counter.
> * tree-ssa-phiopt.c (replace_phi_edge_with_variable):
> Add optional sequence which will be added before the old
> conditional. Check sequence for non-null if we want to
> update the range.
> (two_value_replacement): Instead of inserting the sequence,
> update the call to replace_phi_edge_with_variable.
> (match_simplify_replacement): Likewise.
> (minmax_replacement): Likewise.
> (value_replacement): Create a sequence of statements
> which would have defined the ssa name. Update call
> to replace_phi_edge_with_variable.
>
> gcc/testsuite/ChangeLog:
>
> PR tree-optimization/101256
> * g++.dg/torture/pr101256.C: New test.
> ---
> gcc/dbgcnt.def | 1 +
> gcc/testsuite/g++.dg/torture/pr101256.C | 28 +++++++++++++
> gcc/tree-ssa-phiopt.c | 52 ++++++++++++++-----------
> 3 files changed, 59 insertions(+), 22 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/torture/pr101256.C
>
> diff --git a/gcc/dbgcnt.def b/gcc/dbgcnt.def
> index 93e7b4fd30e..2345899ba68 100644
> --- a/gcc/dbgcnt.def
> +++ b/gcc/dbgcnt.def
> @@ -183,6 +183,7 @@ DEBUG_COUNTER (lim)
> DEBUG_COUNTER (local_alloc_for_sched)
> DEBUG_COUNTER (match)
> DEBUG_COUNTER (merged_ipa_icf)
> +DEBUG_COUNTER (phiopt_edge_range)
> DEBUG_COUNTER (postreload_cse)
> DEBUG_COUNTER (pre)
> DEBUG_COUNTER (pre_insn)
> diff --git a/gcc/testsuite/g++.dg/torture/pr101256.C
> b/gcc/testsuite/g++.dg/torture/pr101256.C
> new file mode 100644
> index 00000000000..973a8b4caf3
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/torture/pr101256.C
> @@ -0,0 +1,28 @@
> +// { dg-do run }
> +
> +template<class T>
> +const T& max(const T& a, const T& b)
> +{
> + return (a < b) ? b : a;
> +}
> +
> +signed char var_5 = -128;
> +unsigned int var_11 = 2144479212U;
> +unsigned long long int arr [22];
> +
> +void
> +__attribute__((noipa))
> +test(signed char var_5, unsigned var_11) {
> + for (short i_61 = 0; i_61 < var_5 + 149; i_61 += 10000)
> + arr[i_61] = max((signed char)0, var_5) ? max((signed char)1, var_5) :
> var_11;
> +}
> +
> +int main() {
> + for (int i_0 = 0; i_0 < 22; ++i_0)
> + arr [i_0] = 11834725929543695741ULL;
> +
> + test(var_5, var_11);
> + if (arr [0] != 2144479212ULL && arr [0] != 11834725929543695741ULL)
> + __builtin_abort ();
> + return 0;
> +}
> diff --git a/gcc/tree-ssa-phiopt.c b/gcc/tree-ssa-phiopt.c
> index ab12e85569d..71f0019d877 100644
> --- a/gcc/tree-ssa-phiopt.c
> +++ b/gcc/tree-ssa-phiopt.c
> @@ -50,6 +50,7 @@ along with GCC; see the file COPYING3. If not see
> #include "gimple-fold.h"
> #include "internal-fn.h"
> #include "gimple-range.h"
> +#include "dbgcnt.h"
>
> static unsigned int tree_ssa_phiopt_worker (bool, bool, bool);
> static bool two_value_replacement (basic_block, basic_block, edge, gphi *,
> @@ -73,7 +74,8 @@ static bool cond_store_replacement (basic_block,
> basic_block, edge, edge,
> hash_set<tree> *);
> static bool cond_if_else_store_replacement (basic_block, basic_block,
> basic_block);
> static hash_set<tree> * get_non_trapping ();
> -static void replace_phi_edge_with_variable (basic_block, edge, gphi *, tree);
> +static void replace_phi_edge_with_variable (basic_block, edge, gphi *, tree,
> + gimple_seq = NULL);
> static void hoist_adjacent_loads (basic_block, basic_block,
> basic_block, basic_block);
> static bool gate_hoist_loads (void);
> @@ -382,18 +384,20 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool
> do_hoist_loads, bool early_p)
>
> /* Replace PHI node element whose edge is E in block BB with variable NEW.
> Remove the edge from COND_BLOCK which does not lead to BB (COND_BLOCK
> - is known to have two edges, one of which must reach BB). */
> + is known to have two edges, one of which must reach BB).
> + Optionally insert stmts before the old condition. */
>
> static void
> replace_phi_edge_with_variable (basic_block cond_block,
> - edge e, gphi *phi, tree new_tree)
> + edge e, gphi *phi, tree new_tree,
> + gimple_seq stmts)
> {
> basic_block bb = gimple_bb (phi);
> basic_block block_to_remove;
> gimple_stmt_iterator gsi;
> tree phi_result = PHI_RESULT (phi);
>
> - /* Duplicate range info if we're the only things setting the target PHI.
> + /* Duplicate range info if they are the only things setting the target PHI.
> This is needed as later on, the new_tree will be replacing
> The assignement of the PHI.
> For an example:
> @@ -401,19 +405,23 @@ replace_phi_edge_with_variable (basic_block cond_block,
> _4 = min<a_1, 255>
> goto bb2
>
> - range<-INF,255>
> + # RANGE [-INF, 255]
> a_3 = PHI<_4(1)>
> bb3:
>
> use(a_3)
> - And _4 gets prograted into the use of a_3 and losing the range info.
> - This can't be done for more than 2 incoming edges as the progration
> - won't happen. */
> + And _4 gets propagated into the use of a_3 and losing the range info.
> + This can't be done for more than 2 incoming edges as the propagation
> + won't happen.
> + This also cannot be done if the name is not defined by statements to
> + be placed before the conditional. */
> if (TREE_CODE (new_tree) == SSA_NAME
> && EDGE_COUNT (gimple_bb (phi)->preds) == 2
> && INTEGRAL_TYPE_P (TREE_TYPE (phi_result))
> && !SSA_NAME_RANGE_INFO (new_tree)
> - && SSA_NAME_RANGE_INFO (phi_result))
> + && SSA_NAME_RANGE_INFO (phi_result)
> + && stmts != NULL
> + && dbg_cnt (phiopt_edge_range))
> duplicate_ssa_name_range_info (new_tree,
> SSA_NAME_RANGE_TYPE (phi_result),
> SSA_NAME_RANGE_INFO (phi_result));
> @@ -443,6 +451,8 @@ replace_phi_edge_with_variable (basic_block cond_block,
>
> /* Eliminate the COND_EXPR at the end of COND_BLOCK. */
> gsi = gsi_last_bb (cond_block);
> + if (stmts)
> + gsi_insert_seq_before (&gsi, stmts, GSI_SAME_STMT);
> gsi_remove (&gsi, true);
>
> statistics_counter_event (cfun, "Replace PHI with variable", 1);
> @@ -802,10 +812,8 @@ two_value_replacement (basic_block cond_bb, basic_block
> middle_bb,
> else
> new_rhs = gimple_build (&stmts, MINUS_EXPR, type, arg, lhs);
> new_rhs = gimple_convert (&stmts, TREE_TYPE (arg0), new_rhs);
> - gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
> - gsi_insert_seq_before (&gsi, stmts, GSI_SAME_STMT);
>
> - replace_phi_edge_with_variable (cond_bb, e1, phi, new_rhs);
> + replace_phi_edge_with_variable (cond_bb, e1, phi, new_rhs, stmts);
>
> /* Note that we optimized this PHI. */
> return true;
> @@ -920,10 +928,8 @@ match_simplify_replacement (basic_block cond_bb,
> basic_block middle_bb,
> gsi_move_before (&gsi1, &gsi);
> reset_flow_sensitive_info (gimple_assign_lhs (stmt_to_move));
> }
> - if (seq)
> - gsi_insert_seq_before (&gsi, seq, GSI_SAME_STMT);
>
> - replace_phi_edge_with_variable (cond_bb, e1, phi, result);
> + replace_phi_edge_with_variable (cond_bb, e1, phi, result, seq);
>
> /* Add Statistic here even though replace_phi_edge_with_variable already
> does it as we want to be able to count when match-simplify happens vs
> @@ -1396,6 +1402,7 @@ value_replacement (basic_block cond_bb, basic_block
> middle_bb,
> && absorbing_element_p (code_def,
> cond_rhs, false, rhs2))))))
> {
> + gimple_seq stmts = NULL;
> gsi = gsi_for_stmt (cond);
> /* Moving ASSIGN might change VR of lhs, e.g. when moving u_6
> def-stmt in:
> @@ -1417,11 +1424,15 @@ value_replacement (basic_block cond_bb, basic_block
> middle_bb,
> tree plhs = gimple_assign_lhs (prep_stmt[i]);
> reset_flow_sensitive_info (plhs);
> gsi_from = gsi_for_stmt (prep_stmt[i]);
> - gsi_move_before (&gsi_from, &gsi);
> + gsi_remove (&gsi_from, false);
> +
> + gimple_seq_add_stmt (&stmts, prep_stmt[i]);
> }
> gsi_from = gsi_for_stmt (assign);
> - gsi_move_before (&gsi_from, &gsi);
> - replace_phi_edge_with_variable (cond_bb, e1, phi, lhs);
> + gsi_remove (&gsi_from, false);
> + gimple_seq_add_stmt (&stmts, assign);
> +
> + replace_phi_edge_with_variable (cond_bb, e1, phi, lhs, stmts);
> return 2;
> }
>
> @@ -1811,10 +1822,7 @@ minmax_replacement (basic_block cond_bb, basic_block
> middle_bb,
> tree phi_result = PHI_RESULT (phi);
> result = gimple_build (&stmts, minmax, TREE_TYPE (phi_result), arg0, arg1);
>
> - gsi = gsi_last_bb (cond_bb);
> - gsi_insert_seq_before (&gsi, stmts, GSI_NEW_STMT);
> -
> - replace_phi_edge_with_variable (cond_bb, e1, phi, result);
> + replace_phi_edge_with_variable (cond_bb, e1, phi, result, stmts);
>
> return true;
> }
> --
> 2.27.0
>
