sra: Cap number of sub-access propagations with a param (PR 93435)

PR 93435 is a perfect SRA bomb.  It initializes an array of 16 chars
element-wise, then uses that to initialize an aggregate that consists
of four such arrays, that one to initialize one four times as big as
the previous one all the way to an aggregate that has 64kb.

This causes the sub-access propagation across assignments to create
thousands of byte-sized artificial accesses which are then eligible to
be replaced - they do facilitate forward propagation but there is
enough of them for DSE to never finish.

This patch avoids that situation by accounting how many of such
replacements can be created per SRA candidate.  The default value of
32 was just the largest power of two that did not slow down
compilation of the testcase, but it should also hopefully be big
enough for any reasonable input that might rely on the optimization.

2020-03-20  Martin Jambor  <mjambor@suse.cz>

	PR tree-optimization/93435
	* params.opt (sra-max-propagations): New parameter.
	* tree-sra.c (propagation_budget): New variable.
	(budget_for_propagation_access): New function.
	(propagate_subaccesses_from_rhs): Use it.
	(propagate_subaccesses_from_lhs): Likewise.
	(propagate_all_subaccesses): Set up and destroy propagation_budget.

	gcc/testsuite/
	* gcc.dg/tree-ssa/pr93435.c: New test.

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 2bb7ccc..c5d3fb9 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,13 @@
+2020-03-20  Martin Jambor  <mjambor@suse.cz>
+
+       PR tree-optimization/93435
+       * params.opt (sra-max-propagations): New parameter.
+       * tree-sra.c (propagation_budget): New variable.
+       (budget_for_propagation_access): New function.
+       (propagate_subaccesses_from_rhs): Use it.
+       (propagate_subaccesses_from_lhs): Likewise.
+       (propagate_all_subaccesses): Set up and destroy propagation_budget.
+
 2020-03-20  Carl Love  <cel@us.ibm.com>
 
        PR/target 87583

diff --git a/gcc/params.opt b/gcc/params.opt
index e39216a..1e484c3 100644 (file)
--- a/gcc/params.opt
+++ b/gcc/params.opt
@@ -844,6 +844,10 @@ Maximum size, in storage units, of an aggregate which should be considered for s
 Common Joined UInteger Var(param_sra_max_scalarization_size_speed) Param Optimization
 Maximum size, in storage units, of an aggregate which should be considered for scalarization when compiling for speed.
 
+-param=sra-max-propagations=
+Common Joined UInteger Var(param_sra_max_propagations) Param Optimization Init(32)
+Maximum number of artificial accesses to enable forward propagation that Scalar Replacement of Aggregates will keep for one local variable.
+
 -param=ssa-name-def-chain-limit=
 Common Joined UInteger Var(param_ssa_name_def_chain_limit) Init(512) Param Optimization
 The maximum number of SSA_NAME assignments to follow in determining a value.

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 50c42e2..ce99c98 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-20  Martin Jambor  <mjambor@suse.cz>
+
+       PR tree-optimization/93435
+       * gcc.dg/tree-ssa/pr93435.c: New test.
+
 2020-03-20  Jan Hubicka  <hubicka@ucw.cz>
 
        PR ipa/93347

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr93435.c b/gcc/testsuite/gcc.dg/tree-ssa/pr93435.c
new file mode 100644 (file)
index 0000000..cb8e749
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr93435.c
@@ -0,0 +1,159 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+typedef signed char int8_T;
+typedef int int32_T;
+
+typedef struct {
+  int8_T a;
+} struct0_T;
+
+typedef struct {
+  struct0_T f10[4];
+} struct_T;
+
+typedef struct {
+  struct_T f9[4];
+} b_struct_T;
+
+typedef struct {
+  b_struct_T f8[4];
+} c_struct_T;
+
+typedef struct {
+  c_struct_T f7[4];
+} d_struct_T;
+
+typedef struct {
+  d_struct_T f6[4];
+} e_struct_T;
+
+typedef struct {
+  e_struct_T f5[4];
+} f_struct_T;
+
+typedef struct {
+  f_struct_T f4[4];
+} g_struct_T;
+
+typedef struct {
+  g_struct_T f3[4];
+} h_struct_T;
+
+typedef struct {
+  h_struct_T f2[4];
+} i_struct_T;
+
+typedef struct {
+  i_struct_T f1[4];
+} j_struct_T;
+
+typedef struct {
+  struct {
+    j_struct_T ds21[4];
+    i_struct_T ds20[4];
+    i_struct_T r9;
+  } f0;
+} deep_struct_arraysStackData;
+
+/* Function Definitions */
+void deep_struct_arrays(deep_struct_arraysStackData *SD,
+  int8_T in1, int8_T inCount, int8_T *out1, int8_T *out2, struct0_T out3[4])
+{
+  struct0_T r;
+  struct_T r1;
+  b_struct_T r2;
+  c_struct_T r3;
+  d_struct_T r4;
+  e_struct_T r5;
+  f_struct_T r6;
+  g_struct_T r7;
+  h_struct_T r8;
+  int32_T count;
+  int32_T i;
+
+  /*  Check properties of input in1 */
+  /*  Check properties of input inCount */
+  /*  Copyright 2006 The MathWorks, Inc. */
+  r.a = in1;
+  r1.f10[0] = r;
+  r1.f10[1] = r;
+  r1.f10[2] = r;
+  r1.f10[3] = r;
+  r2.f9[0] = r1;
+  r2.f9[1] = r1;
+  r2.f9[2] = r1;
+  r2.f9[3] = r1;
+  r3.f8[0] = r2;
+  r3.f8[1] = r2;
+  r3.f8[2] = r2;
+  r3.f8[3] = r2;
+  r4.f7[0] = r3;
+  r4.f7[1] = r3;
+  r4.f7[2] = r3;
+  r4.f7[3] = r3;
+  r5.f6[0] = r4;
+  r5.f6[1] = r4;
+  r5.f6[2] = r4;
+  r5.f6[3] = r4;
+  r6.f5[0] = r5;
+  r6.f5[1] = r5;
+  r6.f5[2] = r5;
+  r6.f5[3] = r5;
+  r7.f4[0] = r6;
+  r7.f4[1] = r6;
+  r7.f4[2] = r6;
+  r7.f4[3] = r6;
+  r8.f3[0] = r7;
+  r8.f3[1] = r7;
+  r8.f3[2] = r7;
+  r8.f3[3] = r7;
+  SD->f0.r9.f2[0] = r8;
+  SD->f0.r9.f2[1] = r8;
+  SD->f0.r9.f2[2] = r8;
+  SD->f0.r9.f2[3] = r8;
+  SD->f0.ds20[0] = SD->f0.r9;
+  SD->f0.ds20[3] = SD->f0.r9;
+  count = 0;
+  while (count < inCount) {
+    i = in1 + SD->f0.ds20[0].f2[0].f3[0].f4[0].f5[0].f6[0].f7[0].f8[0].f9[0]
+      .f10[0].a;
+    if (i > 127) {
+      i = 127;
+    } else {
+      if (i < -128) {
+        i = -128;
+      }
+    }
+
+    SD->f0.ds20[0].f2[0].f3[0].f4[0].f5[0].f6[0].f7[0].f8[0].f9[0].f10[0].a =
+      (int8_T)i;
+    i = SD->f0.ds20[3].f2[3].f3[3].f4[3].f5[3].f6[3].f7[3].f8[3].f9[3].f10[3].a
+      + 3;
+    if (i > 127) {
+      i = 127;
+    }
+
+    SD->f0.ds20[3].f2[3].f3[3].f4[3].f5[3].f6[3].f7[3].f8[3].f9[3].f10[3].a =
+      (int8_T)i;
+    count++;
+  }
+
+  if (inCount > 10) {
+    SD->f0.ds21[0].f1[1].f2[2].f3[3].f4[3].f5[3].f6[3].f7[3].f8[3].f9[3].f10[3].
+      a = 14;
+  } else {
+    SD->f0.ds21[0].f1[1].f2[2].f3[3].f4[3].f5[3].f6[3].f7[3].f8[3].f9[3].f10[3].
+      a = 16;
+  }
+
+  *out1 = SD->f0.ds20[0].f2[0].f3[0].f4[0].f5[0].f6[0].f7[0].f8[0].f9[0].f10[0].
+    a;
+  *out2 = SD->f0.ds20[3].f2[3].f3[3].f4[3].f5[3].f6[3].f7[3].f8[3].f9[3].f10[3].
+    a;
+  out3[0] = r;
+  out3[1] = r;
+  out3[2] = r;
+  out3[3] = SD->f0.ds21[0].f1[1].f2[2].f3[3].f4[3].f5[3].f6[3].f7[3].f8[3].f9[3]
+    .f10[3];
+}

diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
index afff0ec..b2056b5 100644 (file)
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -285,6 +285,9 @@ static object_allocator<assign_link> assign_link_pool ("SRA links");
 /* Base (tree) -> Vector (vec<access_p> *) map.  */
 static hash_map<tree, auto_vec<access_p> > *base_access_vec;
 
+/* Hash to limit creation of artificial accesses */
+static hash_map<tree, unsigned> *propagation_budget;
+
 /* Candidate hash table helpers.  */
 
 struct uid_decl_hasher : nofree_ptr_hash <tree_node>
@@ -2687,6 +2690,32 @@ subtree_mark_written_and_rhs_enqueue (struct access *access)
     subtree_mark_written_and_rhs_enqueue (child);
 }
 
+/* If there is still budget to create a propagation access for DECL, return
+   true and decrement the budget.  Otherwise return false.  */
+
+static bool
+budget_for_propagation_access (tree decl)
+{
+  unsigned b, *p = propagation_budget->get (decl);
+  if (p)
+    b = *p;
+  else
+    b = param_sra_max_propagations;
+
+  if (b == 0)
+    return false;
+  b--;
+
+  if (b == 0 && dump_file && (dump_flags & TDF_DETAILS))
+    {
+      fprintf (dump_file, "The propagation budget of ");
+      print_generic_expr (dump_file, decl);
+      fprintf (dump_file, " (UID: %u) has been exhausted.\n", DECL_UID (decl));
+    }
+  propagation_budget->put (decl, b);
+  return true;
+}
+
 /* Propagate subaccesses and grp_write flags of RACC across an assignment link
    to LACC.  Enqueue sub-accesses as necessary so that the write flag is
    propagated transitively.  Return true if anything changed.  Additionally, if
@@ -2791,7 +2820,8 @@ propagate_subaccesses_from_rhs (struct access *lacc, struct access *racc)
          continue;
        }
 
-      if (rchild->grp_unscalarizable_region)
+      if (rchild->grp_unscalarizable_region
+         || !budget_for_propagation_access (lacc->base))
        {
          if (rchild->grp_write && !lacc->grp_write)
            {
@@ -2851,7 +2881,8 @@ propagate_subaccesses_from_lhs (struct access *lacc, struct access *racc)
 
       if (lchild->grp_unscalarizable_region
          || child_would_conflict_in_acc (racc, norm_offset, lchild->size,
-                                         &matching_acc))
+                                         &matching_acc)
+         || !budget_for_propagation_access (racc->base))
        {
          if (matching_acc
              && propagate_subaccesses_from_lhs (lchild, matching_acc))
@@ -2882,6 +2913,7 @@ propagate_subaccesses_from_lhs (struct access *lacc, struct access *racc)
 static void
 propagate_all_subaccesses (void)
 {
+  propagation_budget = new hash_map<tree, unsigned>;
   while (rhs_work_queue_head)
     {
       struct access *racc = pop_access_from_rhs_work_queue ();
@@ -2945,6 +2977,7 @@ propagate_all_subaccesses (void)
            add_access_to_lhs_work_queue (racc);
        }
     }
+  delete propagation_budget;
 }
 
 /* Return true if the forest beginning with ROOT does not contain