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* [PATCH] combine: Narrow comparison of memory and constant
@ 2023-06-12  7:57 Stefan Schulze Frielinghaus
  2023-06-12 21:29 ` Jeff Law
  0 siblings, 1 reply; 11+ messages in thread
From: Stefan Schulze Frielinghaus @ 2023-06-12  7:57 UTC (permalink / raw)
  To: gcc-patches; +Cc: Stefan Schulze Frielinghaus

Comparisons between memory and constants might be done in a smaller mode
resulting in smaller constants which might finally end up as immediates
instead of in the literal pool.

For example, on s390x a non-symmetric comparison like
  x <= 0x3fffffffffffffff
results in the constant being spilled to the literal pool and an 8 byte
memory comparison is emitted.  Ideally, an equivalent comparison
  x0 <= 0x3f
where x0 is the most significant byte of x, is emitted where the
constant is smaller and more likely to materialize as an immediate.

Similarly, comparisons of the form
  x >= 0x4000000000000000
can be shortened into x0 >= 0x40.

I'm not entirely sure whether combine is the right place to implement
something like this.  In my first try I implemented it in
TARGET_CANONICALIZE_COMPARISON but then thought other targets might
profit from it, too.  simplify_context::simplify_relational_operation_1
seems to be the wrong place since code/mode may change.  Any opinions?

gcc/ChangeLog:

	* combine.cc (simplify_compare_const): Narrow comparison of
	memory and constant.
	(try_combine): Adapt new function signature.
	(simplify_comparison): Adapt new function signature.

gcc/testsuite/ChangeLog:

	* gcc.target/s390/cmp-mem-const-1.c: New test.
	* gcc.target/s390/cmp-mem-const-2.c: New test.
---
 gcc/combine.cc                                | 82 ++++++++++++++-
 .../gcc.target/s390/cmp-mem-const-1.c         | 99 +++++++++++++++++++
 .../gcc.target/s390/cmp-mem-const-2.c         | 23 +++++
 3 files changed, 200 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/s390/cmp-mem-const-1.c
 create mode 100644 gcc/testsuite/gcc.target/s390/cmp-mem-const-2.c

diff --git a/gcc/combine.cc b/gcc/combine.cc
index 5aa0ec5c45a..6ad1600dc1b 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -460,7 +460,7 @@ static rtx simplify_shift_const (rtx, enum rtx_code, machine_mode, rtx,
 static int recog_for_combine (rtx *, rtx_insn *, rtx *);
 static rtx gen_lowpart_for_combine (machine_mode, rtx);
 static enum rtx_code simplify_compare_const (enum rtx_code, machine_mode,
-					     rtx, rtx *);
+					     rtx *, rtx *);
 static enum rtx_code simplify_comparison (enum rtx_code, rtx *, rtx *);
 static void update_table_tick (rtx);
 static void record_value_for_reg (rtx, rtx_insn *, rtx);
@@ -3185,7 +3185,7 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
 	  compare_code = orig_compare_code = GET_CODE (*cc_use_loc);
 	  if (is_a <scalar_int_mode> (GET_MODE (i2dest), &mode))
 	    compare_code = simplify_compare_const (compare_code, mode,
-						   op0, &op1);
+						   &op0, &op1);
 	  target_canonicalize_comparison (&compare_code, &op0, &op1, 1);
 	}
 
@@ -11800,9 +11800,10 @@ gen_lowpart_for_combine (machine_mode omode, rtx x)
 
 static enum rtx_code
 simplify_compare_const (enum rtx_code code, machine_mode mode,
-			rtx op0, rtx *pop1)
+			rtx *pop0, rtx *pop1)
 {
   scalar_int_mode int_mode;
+  rtx op0 = *pop0;
   HOST_WIDE_INT const_op = INTVAL (*pop1);
 
   /* Get the constant we are comparing against and turn off all bits
@@ -11987,6 +11988,79 @@ simplify_compare_const (enum rtx_code code, machine_mode mode,
       break;
     }
 
+  /* Narrow non-symmetric comparison of memory and constant as e.g.
+     x0...x7 <= 0x3fffffffffffffff into x0 <= 0x3f where x0 is the most
+     significant byte.  Likewise, transform x0...x7 >= 0x4000000000000000 into
+     x0 >= 0x40.  */
+  if ((code == LEU || code == LTU || code == GEU || code == GTU)
+      && is_a <scalar_int_mode> (GET_MODE (op0), &int_mode)
+      && MEM_P (op0)
+      && !MEM_VOLATILE_P (op0)
+      && (unsigned HOST_WIDE_INT)const_op > 0xff)
+    {
+      unsigned HOST_WIDE_INT n = (unsigned HOST_WIDE_INT)const_op;
+      enum rtx_code adjusted_code = code;
+
+      /* If the least significant bit is already zero, then adjust the
+	 comparison in the hope that we hit cases like
+	   op0  <= 0x3ffffdfffffffffe
+	 where the adjusted comparison
+	   op0  <  0x3ffffdffffffffff
+	 can be shortened into
+	   op0' <  0x3ffffd.  */
+      if (code == LEU && (n & 1) == 0)
+	{
+	  ++n;
+	  adjusted_code = LTU;
+	}
+      /* or e.g. op0 < 0x4020000000000000  */
+      else if (code == LTU && (n & 1) == 0)
+	{
+	  --n;
+	  adjusted_code = LEU;
+	}
+      /* or op0 >= 0x4000000000000001  */
+      else if (code == GEU && (n & 1) == 1)
+	{
+	  --n;
+	  adjusted_code = GTU;
+	}
+      /* or op0 > 0x3fffffffffffffff.  */
+      else if (code == GTU && (n & 1) == 1)
+	{
+	  ++n;
+	  adjusted_code = GEU;
+	}
+
+      scalar_int_mode narrow_mode_iter;
+      bool lower_p = code == LEU || code == LTU;
+      bool greater_p = !lower_p;
+      FOR_EACH_MODE_UNTIL (narrow_mode_iter, int_mode)
+	{
+	  unsigned nbits = GET_MODE_PRECISION (int_mode)
+			  - GET_MODE_PRECISION (narrow_mode_iter);
+	  unsigned HOST_WIDE_INT mask = (HOST_WIDE_INT_1U << nbits) - 1;
+	  unsigned HOST_WIDE_INT lower_bits = n & mask;
+	  if ((lower_p && lower_bits == mask)
+	      || (greater_p && lower_bits == 0))
+	    {
+	      n >>= nbits;
+	      break;
+	    }
+	}
+
+      if (narrow_mode_iter < int_mode)
+	{
+	  poly_int64 offset = BYTES_BIG_ENDIAN
+				? 0
+				: GET_MODE_SIZE (int_mode)
+				  - GET_MODE_SIZE (narrow_mode_iter);
+	  *pop0 = adjust_address (op0, narrow_mode_iter, offset);
+	  *pop1 = GEN_INT (n);
+	  return adjusted_code;
+	}
+    }
+
   *pop1 = GEN_INT (const_op);
   return code;
 }
@@ -12179,7 +12253,7 @@ simplify_comparison (enum rtx_code code, rtx *pop0, rtx *pop1)
 
       /* Try to simplify the compare to constant, possibly changing the
 	 comparison op, and/or changing op1 to zero.  */
-      code = simplify_compare_const (code, raw_mode, op0, &op1);
+      code = simplify_compare_const (code, raw_mode, &op0, &op1);
       const_op = INTVAL (op1);
 
       /* Compute some predicates to simplify code below.  */
diff --git a/gcc/testsuite/gcc.target/s390/cmp-mem-const-1.c b/gcc/testsuite/gcc.target/s390/cmp-mem-const-1.c
new file mode 100644
index 00000000000..b90c2a8c224
--- /dev/null
+++ b/gcc/testsuite/gcc.target/s390/cmp-mem-const-1.c
@@ -0,0 +1,99 @@
+/* { dg-do compile { target { lp64 } } } */
+/* { dg-options "-O1 -march=z13 -mzarch" } */
+/* { dg-final { scan-assembler-not {\tclc\t} } } */
+
+int
+ge_8b (unsigned long *x)
+{
+  return *x >= 0x4000000000000000;
+}
+
+int
+ge_8b_adjust (unsigned long *x)
+{
+  return *x >= 0x4000000000000001;
+}
+
+int
+ge_6b (unsigned long *x)
+{
+  return *x >= 0x400000000000;
+}
+
+int
+ge_6b_adjust (unsigned long *x)
+{
+  return *x >= 0x400000000001;
+}
+
+int
+gt_8b (unsigned long *x)
+{
+  return *x > 0x4000000000000000;
+}
+
+int
+gt_8b_adjust (unsigned long *x)
+{
+  return *x > 0x3fffffffffffffff;
+}
+
+int
+gt_6b (unsigned long *x)
+{
+  return *x > 0x400000000000;
+}
+
+int
+gt_6b_adjust (unsigned long *x)
+{
+  return *x > 0x3fffffffffff;
+}
+
+int
+le_8b (unsigned long *x)
+{
+  return *x <= 0x3ff7ffffffffffff;
+}
+
+int
+le_6b (unsigned long *x)
+{
+  return *x <= 0x3f7fffffffff;
+}
+
+int
+le_8b_adjust (unsigned long *x)
+{
+  return *x <= 0x3ffffdfffffffffe;
+}
+
+int
+le_6b_adjust (unsigned long *x)
+{
+  return *x <= 0x3ffffffffffe;
+}
+
+int
+lt_8b (unsigned long *x)
+{
+  return *x < 0x3fffffffffffffff;
+}
+
+int
+lt_6b (unsigned long *x)
+{
+  return *x < 0x3fffffffffff;
+}
+
+int
+lt_8b_adjust (unsigned long *x)
+{
+  return *x < 0x4020000000000000;
+}
+
+int
+lt_6b_adjust (unsigned long *x)
+{
+  return *x < 0x400000000000;
+}
diff --git a/gcc/testsuite/gcc.target/s390/cmp-mem-const-2.c b/gcc/testsuite/gcc.target/s390/cmp-mem-const-2.c
new file mode 100644
index 00000000000..e3951870d94
--- /dev/null
+++ b/gcc/testsuite/gcc.target/s390/cmp-mem-const-2.c
@@ -0,0 +1,23 @@
+/* { dg-do compile { target { lp64 } } } */
+/* { dg-options "-O1 -march=z13 -mzarch" } */
+/* { dg-final { scan-assembler-not {\tclc\t} } } */
+
+struct s
+{
+  long a;
+  unsigned b : 1;
+  unsigned c : 1;
+};
+
+int foo (struct s *x)
+{
+  /* Expression
+       x->b || x->c
+     is transformed into
+       _1 = BIT_FIELD_REF <*x_4(D), 64, 64>;
+       _2 = _1 > 0x3FFFFFFFFFFFFFFF;
+     where the constant may materialize in the literal pool and an 8 byte CLC
+     may be emitted.  Ensure this is not the case.
+  */
+  return x->b || x->c;
+}
-- 
2.39.2


^ permalink raw reply	[flat|nested] 11+ messages in thread
end of thread, other threads:[~2023-08-01  9:36 UTC | newest]

Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-06-12  7:57 [PATCH] combine: Narrow comparison of memory and constant Stefan Schulze Frielinghaus
2023-06-12 21:29 ` Jeff Law
2023-06-19 14:19   ` Stefan Schulze Frielinghaus
2023-06-19 14:23     ` [PATCH v2] " Stefan Schulze Frielinghaus
2023-07-31 13:26       ` Stefan Schulze Frielinghaus
2023-07-31 13:59       ` Jeff Law
2023-07-31 21:43       ` Prathamesh Kulkarni
2023-07-31 21:46         ` Prathamesh Kulkarni
2023-07-31 23:50         ` Jeff Law
2023-08-01  8:22           ` Prathamesh Kulkarni
2023-08-01  9:36             ` Stefan Schulze Frielinghaus

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