[PATCH] Fix compile/memory hog in the combiner (PR rtl-optimization/69592)

[Jakub Jelinek]

Hi!

On the following testcase we completely uselessly consume about 5.5GB
of RAM and lots of compile time.  The problem is the code to avoid
exponential behavior of nonzero_bits/num_sign_bit_copies on binary
arithmetics rtxes, which causes us to recurse even when handling
of those rtxes is going to ignore those arguments.
So, this patch limits those only to the cases where we are going
to recurse on both arguments, for rtxes where we don't look at arguments
at all or where we only recurse on a single arguments it doesn't make
sense.  On the testcase, one of the rtxes where the new predicates
return false but ARITHMETIC_P is true, is COMPARE, in particular
(compare:CCC (plus (x) (y)) (x)), where it is known even without
looking at the operands that only one bit is possibly non-zero and
number of sign bit copies is always 1.  But without the patch we
needlessly recurse on x, which is set by another similar operation etc.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2016-02-01  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/69592
	* rtlanal.c (nonzero_bits_binary_arith_p): New inline function.
	(cached_nonzero_bits): Use it instead of ARITHMETIC_P.
	(num_sign_bit_copies_binary_arith_p): New inline function.
	(cached_num_sign_bit_copies): Use it instead of ARITHMETIC_P.

	* gcc.dg/pr69592.c: New test.

--- gcc/rtlanal.c.jj	2016-01-21 21:27:57.000000000 +0100
+++ gcc/rtlanal.c	2016-02-01 18:53:06.130934333 +0100
@@ -4163,6 +4163,36 @@ num_sign_bit_copies (const_rtx x, machin
   return cached_num_sign_bit_copies (x, mode, NULL_RTX, VOIDmode, 0);
 }
 
+/* Return true if nonzero_bits1 might recurse into both operands
+   of X.  */
+
+static inline bool
+nonzero_bits_binary_arith_p (const_rtx x)
+{
+  if (!ARITHMETIC_P (x))
+    return false;
+  switch (GET_CODE (x))
+    {
+    case AND:
+    case XOR:
+    case IOR:
+    case UMIN:
+    case UMAX:
+    case SMIN:
+    case SMAX:
+    case PLUS:
+    case MINUS:
+    case MULT:
+    case DIV:
+    case UDIV:
+    case MOD:
+    case UMOD:
+      return true;
+    default:
+      return false;
+    }
+}
+
 /* The function cached_nonzero_bits is a wrapper around nonzero_bits1.
    It avoids exponential behavior in nonzero_bits1 when X has
    identical subexpressions on the first or the second level.  */
@@ -4179,7 +4209,7 @@ cached_nonzero_bits (const_rtx x, machin
      nonzero_bits1 on X with the subexpressions as KNOWN_X and the
      precomputed value for the subexpression as KNOWN_RET.  */
 
-  if (ARITHMETIC_P (x))
+  if (nonzero_bits_binary_arith_p (x))
     {
       rtx x0 = XEXP (x, 0);
       rtx x1 = XEXP (x, 1);
@@ -4191,13 +4221,13 @@ cached_nonzero_bits (const_rtx x, machin
 						   known_mode, known_ret));
 
       /* Check the second level.  */
-      if (ARITHMETIC_P (x0)
+      if (nonzero_bits_binary_arith_p (x0)
 	  && (x1 == XEXP (x0, 0) || x1 == XEXP (x0, 1)))
 	return nonzero_bits1 (x, mode, x1, mode,
 			      cached_nonzero_bits (x1, mode, known_x,
 						   known_mode, known_ret));
 
-      if (ARITHMETIC_P (x1)
+      if (nonzero_bits_binary_arith_p (x1)
 	  && (x0 == XEXP (x1, 0) || x0 == XEXP (x1, 1)))
 	return nonzero_bits1 (x, mode, x0, mode,
 			      cached_nonzero_bits (x0, mode, known_x,
@@ -4672,6 +4702,33 @@ nonzero_bits1 (const_rtx x, machine_mode
 #undef cached_num_sign_bit_copies
 
 
+/* Return true if num_sign_bit_copies1 might recurse into both operands
+   of X.  */
+
+static inline bool
+num_sign_bit_copies_binary_arith_p (const_rtx x)
+{
+  if (!ARITHMETIC_P (x))
+    return false;
+  switch (GET_CODE (x))
+    {
+    case IOR:
+    case AND:
+    case XOR:
+    case SMIN:
+    case SMAX:
+    case UMIN:
+    case UMAX:
+    case PLUS:
+    case MINUS:
+    case MULT:
+      return true;
+    default:
+      return false;
+    }
+}
+
+
 /* The function cached_num_sign_bit_copies is a wrapper around
    num_sign_bit_copies1.  It avoids exponential behavior in
    num_sign_bit_copies1 when X has identical subexpressions on the
@@ -4689,7 +4746,7 @@ cached_num_sign_bit_copies (const_rtx x,
      num_sign_bit_copies1 on X with the subexpressions as KNOWN_X and
      the precomputed value for the subexpression as KNOWN_RET.  */
 
-  if (ARITHMETIC_P (x))
+  if (num_sign_bit_copies_binary_arith_p (x))
     {
       rtx x0 = XEXP (x, 0);
       rtx x1 = XEXP (x, 1);
@@ -4703,7 +4760,7 @@ cached_num_sign_bit_copies (const_rtx x,
 							    known_ret));
 
       /* Check the second level.  */
-      if (ARITHMETIC_P (x0)
+      if (num_sign_bit_copies_binary_arith_p (x0)
 	  && (x1 == XEXP (x0, 0) || x1 == XEXP (x0, 1)))
 	return
 	  num_sign_bit_copies1 (x, mode, x1, mode,
@@ -4711,7 +4768,7 @@ cached_num_sign_bit_copies (const_rtx x,
 							    known_mode,
 							    known_ret));
 
-      if (ARITHMETIC_P (x1)
+      if (num_sign_bit_copies_binary_arith_p (x1)
 	  && (x0 == XEXP (x1, 0) || x0 == XEXP (x1, 1)))
 	return
 	  num_sign_bit_copies1 (x, mode, x0, mode,
--- gcc/testsuite/gcc.dg/pr69592.c.jj	2016-02-01 19:02:23.122251761 +0100
+++ gcc/testsuite/gcc.dg/pr69592.c	2016-02-01 19:00:30.000000000 +0100
@@ -0,0 +1,16 @@
+/* PR rtl-optimization/69592 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+unsigned int
+foo (unsigned int a, unsigned int *b, unsigned int c)
+{
+  unsigned int d;
+#define A(n) d = a + b[n]; if (d < a) c++; a = d;
+#define B(n) A(n##0) A(n##1) A(n##2) A(n##3) A(n##4) A(n##5) A(n##6) A(n##7) A(n##8) A(n##9)
+#define C(n) B(n##0) B(n##1) B(n##2) B(n##3) B(n##4) B(n##5) B(n##6) B(n##7) B(n##8) B(n##9)
+#define D(n) C(n##0) C(n##1) C(n##2) C(n##3) C(n##4) C(n##5) C(n##6) C(n##7) C(n##8) C(n##9)
+#define E(n) D(n##0) D(n##1) D(n##2) D(n##3) D(n##4) D(n##5) D(n##6) D(n##7) D(n##8) D(n##9)
+  C(1) C(2) C(3) C(4) C(5) C(6)
+  return d + c;
+}

	Jakub