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.

1 files changed, 159 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr93435.c b/gcc/testsuite/gcc.dg/tree-ssa/pr93435.c
new file mode 100644
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];
+}