sccvn: Handle bitfields in vn_reference_lookup_3 [PR93582]

The following patch is first step towards fixing PR93582.
vn_reference_lookup_3 right now punts on anything that isn't byte aligned,
so to be able to lookup a constant bitfield store, one needs to use
the exact same COMPONENT_REF, otherwise it isn't found.

This patch lifts up that that restriction if the bits to be loaded are
covered by a single store of a constant (keeps the restriction so far
for the multiple store case, can tweak that incrementally, but I think
for bisection etc. it is worth to do it one step at a time).

2020-02-13  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/93582
	* fold-const.h (shift_bytes_in_array_left,
	shift_bytes_in_array_right): Declare.
	* fold-const.c (shift_bytes_in_array_left,
	shift_bytes_in_array_right): New function, moved from
	gimple-ssa-store-merging.c, no longer static.
	* gimple-ssa-store-merging.c (shift_bytes_in_array): Move
	to gimple-ssa-store-merging.c and rename to shift_bytes_in_array_left.
	(shift_bytes_in_array_right): Move to gimple-ssa-store-merging.c.
	(encode_tree_to_bitpos): Use shift_bytes_in_array_left instead of
	shift_bytes_in_array.
	(verify_shift_bytes_in_array): Rename to ...
	(verify_shift_bytes_in_array_left): ... this.  Use
	shift_bytes_in_array_left instead of shift_bytes_in_array.
	(store_merging_c_tests): Call verify_shift_bytes_in_array_left
	instead of verify_shift_bytes_in_array.
	* tree-ssa-sccvn.c (vn_reference_lookup_3): For native_encode_expr
	/ native_interpret_expr where the store covers all needed bits,
	punt on PDP-endian, otherwise allow all involved offsets and sizes
	not to be byte-aligned.

	* gcc.dg/tree-ssa/pr93582-1.c: New test.
	* gcc.dg/tree-ssa/pr93582-2.c: New test.
	* gcc.dg/tree-ssa/pr93582-3.c: New test.

9 files changed, 222 insertions, 88 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 252e820..36a8956 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,26 @@
 2020-02-13  Jakub Jelinek  <jakub@redhat.com>
 
+	PR tree-optimization/93582
+	* fold-const.h (shift_bytes_in_array_left,
+	shift_bytes_in_array_right): Declare.
+	* fold-const.c (shift_bytes_in_array_left,
+	shift_bytes_in_array_right): New function, moved from
+	gimple-ssa-store-merging.c, no longer static.
+	* gimple-ssa-store-merging.c (shift_bytes_in_array): Move
+	to gimple-ssa-store-merging.c and rename to shift_bytes_in_array_left.
+	(shift_bytes_in_array_right): Move to gimple-ssa-store-merging.c.
+	(encode_tree_to_bitpos): Use shift_bytes_in_array_left instead of
+	shift_bytes_in_array.
+	(verify_shift_bytes_in_array): Rename to ...
+	(verify_shift_bytes_in_array_left): ... this.  Use
+	shift_bytes_in_array_left instead of shift_bytes_in_array.
+	(store_merging_c_tests): Call verify_shift_bytes_in_array_left
+	instead of verify_shift_bytes_in_array.
+	* tree-ssa-sccvn.c (vn_reference_lookup_3): For native_encode_expr
+	/ native_interpret_expr where the store covers all needed bits,
+	punt on PDP-endian, otherwise allow all involved offsets and sizes
+	not to be byte-aligned.
+
 	PR target/93673
 	* config/i386/sse.md (k<code><mode>): Drop mode from last operand and
 	use const_0_to_255_operand predicate instead of immediate_operand.
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index aefa916..71a1d3e 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -8354,6 +8354,70 @@ can_native_interpret_type_p (tree type)
     }
 }
 
+/* Routines for manipulation of native_encode_expr encoded data if the encoded
+   or extracted constant positions and/or sizes aren't byte aligned.  */
+
+/* Shift left the bytes in PTR of SZ elements by AMNT bits, carrying over the
+   bits between adjacent elements.  AMNT should be within
+   [0, BITS_PER_UNIT).
+   Example, AMNT = 2:
+   00011111|11100000 << 2 = 01111111|10000000
+   PTR[1]  | PTR[0]         PTR[1]  | PTR[0].  */
+
+void
+shift_bytes_in_array_left (unsigned char *ptr, unsigned int sz,
+			   unsigned int amnt)
+{
+  if (amnt == 0)
+    return;
+
+  unsigned char carry_over = 0U;
+  unsigned char carry_mask = (~0U) << (unsigned char) (BITS_PER_UNIT - amnt);
+  unsigned char clear_mask = (~0U) << amnt;
+
+  for (unsigned int i = 0; i < sz; i++)
+    {
+      unsigned prev_carry_over = carry_over;
+      carry_over = (ptr[i] & carry_mask) >> (BITS_PER_UNIT - amnt);
+
+      ptr[i] <<= amnt;
+      if (i != 0)
+	{
+	  ptr[i] &= clear_mask;
+	  ptr[i] |= prev_carry_over;
+	}
+    }
+}
+
+/* Like shift_bytes_in_array_left but for big-endian.
+   Shift right the bytes in PTR of SZ elements by AMNT bits, carrying over the
+   bits between adjacent elements.  AMNT should be within
+   [0, BITS_PER_UNIT).
+   Example, AMNT = 2:
+   00011111|11100000 >> 2 = 00000111|11111000
+   PTR[0]  | PTR[1]         PTR[0]  | PTR[1].  */
+
+void
+shift_bytes_in_array_right (unsigned char *ptr, unsigned int sz,
+			    unsigned int amnt)
+{
+  if (amnt == 0)
+    return;
+
+  unsigned char carry_over = 0U;
+  unsigned char carry_mask = ~(~0U << amnt);
+
+  for (unsigned int i = 0; i < sz; i++)
+    {
+      unsigned prev_carry_over = carry_over;
+      carry_over = ptr[i] & carry_mask;
+
+      carry_over <<= (unsigned char) BITS_PER_UNIT - amnt;
+      ptr[i] >>= amnt;
+      ptr[i] |= prev_carry_over;
+    }
+}
+
 /* Try to view-convert VECTOR_CST EXPR to VECTOR_TYPE TYPE by operating
    directly on the VECTOR_CST encoding, in a way that works for variable-
    length vectors.  Return the resulting VECTOR_CST on success or null
diff --git a/gcc/fold-const.h b/gcc/fold-const.h
index 7ac792f..0f788a4 100644
--- a/gcc/fold-const.h
+++ b/gcc/fold-const.h
@@ -30,6 +30,10 @@ extern int native_encode_initializer (tree, unsigned char *, int,
 				      int off = -1);
 extern tree native_interpret_expr (tree, const unsigned char *, int);
 extern bool can_native_interpret_type_p (tree);
+extern void shift_bytes_in_array_left (unsigned char *, unsigned int,
+				       unsigned int);
+extern void shift_bytes_in_array_right (unsigned char *, unsigned int,
+					unsigned int);
 
 /* Fold constants as much as possible in an expression.
    Returns the simplified expression.
diff --git a/gcc/gimple-ssa-store-merging.c b/gcc/gimple-ssa-store-merging.c
index 8371323..4bcafef 100644
--- a/gcc/gimple-ssa-store-merging.c
+++ b/gcc/gimple-ssa-store-merging.c
@@ -1475,66 +1475,6 @@ dump_char_array (FILE *fd, unsigned char *ptr, unsigned int len)
   fprintf (fd, "\n");
 }
 
-/* Shift left the bytes in PTR of SZ elements by AMNT bits, carrying over the
-   bits between adjacent elements.  AMNT should be within
-   [0, BITS_PER_UNIT).
-   Example, AMNT = 2:
-   00011111|11100000 << 2 = 01111111|10000000
-   PTR[1]  | PTR[0]         PTR[1]  | PTR[0].  */
-
-static void
-shift_bytes_in_array (unsigned char *ptr, unsigned int sz, unsigned int amnt)
-{
-  if (amnt == 0)
-    return;
-
-  unsigned char carry_over = 0U;
-  unsigned char carry_mask = (~0U) << (unsigned char) (BITS_PER_UNIT - amnt);
-  unsigned char clear_mask = (~0U) << amnt;
-
-  for (unsigned int i = 0; i < sz; i++)
-    {
-      unsigned prev_carry_over = carry_over;
-      carry_over = (ptr[i] & carry_mask) >> (BITS_PER_UNIT - amnt);
-
-      ptr[i] <<= amnt;
-      if (i != 0)
-	{
-	  ptr[i] &= clear_mask;
-	  ptr[i] |= prev_carry_over;
-	}
-    }
-}
-
-/* Like shift_bytes_in_array but for big-endian.
-   Shift right the bytes in PTR of SZ elements by AMNT bits, carrying over the
-   bits between adjacent elements.  AMNT should be within
-   [0, BITS_PER_UNIT).
-   Example, AMNT = 2:
-   00011111|11100000 >> 2 = 00000111|11111000
-   PTR[0]  | PTR[1]         PTR[0]  | PTR[1].  */
-
-static void
-shift_bytes_in_array_right (unsigned char *ptr, unsigned int sz,
-			    unsigned int amnt)
-{
-  if (amnt == 0)
-    return;
-
-  unsigned char carry_over = 0U;
-  unsigned char carry_mask = ~(~0U << amnt);
-
-  for (unsigned int i = 0; i < sz; i++)
-    {
-      unsigned prev_carry_over = carry_over;
-      carry_over = ptr[i] & carry_mask;
-
-      carry_over <<= (unsigned char) BITS_PER_UNIT - amnt;
-      ptr[i] >>= amnt;
-      ptr[i] |= prev_carry_over;
-    }
-}
-
 /* Clear out LEN bits starting from bit START in the byte array
    PTR.  This clears the bits to the *right* from START.
    START must be within [0, BITS_PER_UNIT) and counts starting from
@@ -1793,7 +1733,7 @@ encode_tree_to_bitpos (tree expr, unsigned char *ptr, int bitlen, int bitpos,
   /* Create the shifted version of EXPR.  */
   if (!BYTES_BIG_ENDIAN)
     {
-      shift_bytes_in_array (tmpbuf, byte_size, shift_amnt);
+      shift_bytes_in_array_left (tmpbuf, byte_size, shift_amnt);
       if (shift_amnt == 0)
 	byte_size--;
     }
@@ -5092,11 +5032,11 @@ verify_array_eq (unsigned char *x, unsigned char *y, unsigned int n)
     }
 }
 
-/* Test shift_bytes_in_array and that it carries bits across between
+/* Test shift_bytes_in_array_left and that it carries bits across between
    bytes correctly.  */
 
 static void
-verify_shift_bytes_in_array (void)
+verify_shift_bytes_in_array_left (void)
 {
    /* byte 1   | byte 0
       00011111 | 11100000.  */
@@ -5105,13 +5045,13 @@ verify_shift_bytes_in_array (void)
   memcpy (in, orig, sizeof orig);
 
   unsigned char expected[2] = { 0x80, 0x7f };
-  shift_bytes_in_array (in, sizeof (in), 2);
+  shift_bytes_in_array_left (in, sizeof (in), 2);
   verify_array_eq (in, expected, sizeof (in));
 
   memcpy (in, orig, sizeof orig);
   memcpy (expected, orig, sizeof orig);
   /* Check that shifting by zero doesn't change anything.  */
-  shift_bytes_in_array (in, sizeof (in), 0);
+  shift_bytes_in_array_left (in, sizeof (in), 0);
   verify_array_eq (in, expected, sizeof (in));
 
 }
@@ -5196,7 +5136,7 @@ verify_clear_bit_region_be (void)
 void
 store_merging_c_tests (void)
 {
-  verify_shift_bytes_in_array ();
+  verify_shift_bytes_in_array_left ();
   verify_shift_bytes_in_array_right ();
   verify_clear_bit_region ();
   verify_clear_bit_region_be ();
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 63d3ff5..2541353 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2020-02-13  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/93582
+	* gcc.dg/tree-ssa/pr93582-1.c: New test.
+	* gcc.dg/tree-ssa/pr93582-2.c: New test.
+	* gcc.dg/tree-ssa/pr93582-3.c: New test.
+
 2020-02-13  Richard Biener  <rguenther@suse.de>
 
 	PR testsuite/93717
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr93582-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr93582-1.c
new file mode 100644
index 0000000..a9f0e34
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr93582-1.c
@@ -0,0 +1,17 @@
+/* PR tree-optimization/93582 */
+/* { dg-do compile { target int32 } } */
+/* { dg-options "-O2 -fdump-tree-fre1" } */
+/* { dg-final { scan-tree-dump "return 1;" "fre1" } } */
+
+union U {
+  struct S { int a : 1, b : 4, c : 27; } s;
+  struct T { int d : 2; int e : 2; int f : 28; } t;
+};
+
+int
+foo (void)
+{
+  union U u;
+  u.s.b = 10;
+  return u.t.e;
+}
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr93582-2.c b/gcc/testsuite/gcc.dg/tree-ssa/pr93582-2.c
new file mode 100644
index 0000000..76d03ec
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr93582-2.c
@@ -0,0 +1,17 @@
+/* PR tree-optimization/93582 */
+/* { dg-do compile { target int32 } } */
+/* { dg-options "-O2 -fdump-tree-fre1" } */
+/* { dg-final { scan-tree-dump "return 593;" "fre1" } } */
+
+union U {
+  struct S { int a : 1, b : 14, c : 17; } s;
+  struct T { int d : 2; int e : 12; int f : 18; } t;
+};
+
+int
+foo (void)
+{
+  union U u;
+  u.s.b = -7005;
+  return u.t.e;
+}
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr93582-3.c b/gcc/testsuite/gcc.dg/tree-ssa/pr93582-3.c
new file mode 100644
index 0000000..84f54fc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr93582-3.c
@@ -0,0 +1,18 @@
+/* PR tree-optimization/93582 */
+/* { dg-do compile { target int32 } } */
+/* { dg-options "-O2 -fdump-tree-fre1" } */
+/* { dg-final { scan-tree-dump "return 1;" "fre1" { target be } } } */
+/* { dg-final { scan-tree-dump "return 2;" "fre1" { target le } } } */
+
+union U {
+  struct S { int a : 1, b : 14, c : 17; } s;
+  struct T { int d : 10; int e : 4; int f : 18; } t;
+};
+
+int
+foo (void)
+{
+  union U u;
+  u.s.b = -7005;
+  return u.t.e;
+}
diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index 33cd12b..30518ab 100644
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -2586,13 +2586,13 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
 	   && is_gimple_reg_type (vr->type)
 	   && !contains_storage_order_barrier_p (vr->operands)
 	   && gimple_assign_single_p (def_stmt)
-	   && CHAR_BIT == 8 && BITS_PER_UNIT == 8
+	   && CHAR_BIT == 8
+	   && BITS_PER_UNIT == 8
+	   && BYTES_BIG_ENDIAN == WORDS_BIG_ENDIAN
 	   /* native_encode and native_decode operate on arrays of bytes
 	      and so fundamentally need a compile-time size and offset.  */
 	   && maxsize.is_constant (&maxsizei)
-	   && maxsizei % BITS_PER_UNIT == 0
 	   && offset.is_constant (&offseti)
-	   && offseti % BITS_PER_UNIT == 0
 	   && (is_gimple_min_invariant (gimple_assign_rhs1 (def_stmt))
 	       || (TREE_CODE (gimple_assign_rhs1 (def_stmt)) == SSA_NAME
 		   && is_gimple_min_invariant (SSA_VAL (gimple_assign_rhs1 (def_stmt))))))
@@ -2617,8 +2617,6 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
 	  && !reverse
 	  && !storage_order_barrier_p (lhs)
 	  && known_eq (maxsize2, size2)
-	  && multiple_p (size2, BITS_PER_UNIT)
-	  && multiple_p (offset2, BITS_PER_UNIT)
 	  && adjust_offsets_for_equal_base_address (base, &offset,
 						    base2, &offset2)
 	  && offset.is_constant (&offseti)
@@ -2629,37 +2627,80 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
 	      && known_subrange_p (offseti, maxsizei, offset2, size2))
 	    {
 	      /* We support up to 512-bit values (for V8DFmode).  */
-	      unsigned char buffer[64];
+	      unsigned char buffer[65];
 	      int len;
 
 	      tree rhs = gimple_assign_rhs1 (def_stmt);
 	      if (TREE_CODE (rhs) == SSA_NAME)
 		rhs = SSA_VAL (rhs);
-	      unsigned pad = 0;
-	      if (BYTES_BIG_ENDIAN
-		  && is_a <scalar_mode> (TYPE_MODE (TREE_TYPE (rhs))))
-		{
-		  /* On big-endian the padding is at the 'front' so
-		     just skip the initial bytes.  */
-		  fixed_size_mode mode
-		    = as_a <fixed_size_mode> (TYPE_MODE (TREE_TYPE (rhs)));
-		  pad = GET_MODE_SIZE (mode) - size2i / BITS_PER_UNIT;
-		}
 	      len = native_encode_expr (rhs,
-					buffer, sizeof (buffer),
-					((offseti - offset2i) / BITS_PER_UNIT
-					 + pad));
+					buffer, sizeof (buffer) - 1,
+					(offseti - offset2i) / BITS_PER_UNIT);
 	      if (len > 0 && len * BITS_PER_UNIT >= maxsizei)
 		{
 		  tree type = vr->type;
+		  unsigned char *buf = buffer;
+		  unsigned int amnt = 0;
 		  /* Make sure to interpret in a type that has a range
 		     covering the whole access size.  */
 		  if (INTEGRAL_TYPE_P (vr->type)
 		      && maxsizei != TYPE_PRECISION (vr->type))
 		    type = build_nonstandard_integer_type (maxsizei,
 							   TYPE_UNSIGNED (type));
-		  tree val = native_interpret_expr (type, buffer,
-						    maxsizei / BITS_PER_UNIT);
+		  if (BYTES_BIG_ENDIAN)
+		    {
+		      /* For big-endian native_encode_expr stored the rhs
+			 such that the LSB of it is the LSB of buffer[len - 1].
+			 That bit is stored into memory at position
+			 offset2 + size2 - 1, i.e. in byte
+			 base + (offset2 + size2 - 1) / BITS_PER_UNIT.
+			 E.g. for offset2 1 and size2 14, rhs -1 and memory
+			 previously cleared that is:
+			 0        1
+			 01111111|11111110
+			 Now, if we want to extract offset 2 and size 12 from
+			 it using native_interpret_expr (which actually works
+			 for integral bitfield types in terms of byte size of
+			 the mode), the native_encode_expr stored the value
+			 into buffer as
+			 XX111111|11111111
+			 and returned len 2 (the X bits are outside of
+			 precision).
+			 Let sz be maxsize / BITS_PER_UNIT if not extracting
+			 a bitfield, and GET_MODE_SIZE otherwise.
+			 We need to align the LSB of the value we want to
+			 extract as the LSB of buf[sz - 1].
+			 The LSB from memory we need to read is at position
+			 offset + maxsize - 1.  */
+		      HOST_WIDE_INT sz = maxsizei / BITS_PER_UNIT;
+		      if (INTEGRAL_TYPE_P (type))
+			sz = GET_MODE_SIZE (SCALAR_INT_TYPE_MODE (type));
+		      amnt = ((unsigned HOST_WIDE_INT) offset2i + size2i
+			      - offseti - maxsizei) % BITS_PER_UNIT;
+		      if (amnt)
+			shift_bytes_in_array_right (buffer, len, amnt);
+		      amnt = ((unsigned HOST_WIDE_INT) offset2i + size2i
+			      - offseti - maxsizei - amnt) / BITS_PER_UNIT;
+		      if ((unsigned HOST_WIDE_INT) sz + amnt > (unsigned) len)
+			len = 0;
+		      else
+			{
+			  buf = buffer + len - sz - amnt;
+			  len -= (buf - buffer);
+			}
+		    }
+		  else
+		    {
+		      amnt = ((unsigned HOST_WIDE_INT) offset2i
+			      - offseti) % BITS_PER_UNIT;
+		      if (amnt)
+			{
+			  buffer[len] = 0;
+			  shift_bytes_in_array_left (buffer, len + 1, amnt);
+			  buf = buffer + 1;
+			}
+		    }
+		  tree val = native_interpret_expr (type, buf, len);
 		  /* If we chop off bits because the types precision doesn't
 		     match the memory access size this is ok when optimizing
 		     reads but not when called from the DSE code during
@@ -2677,7 +2718,12 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
 		    return data->finish (get_alias_set (lhs), val);
 		}
 	    }
-	  else if (ranges_known_overlap_p (offseti, maxsizei, offset2i, size2i))
+	  else if (ranges_known_overlap_p (offseti, maxsizei, offset2i,
+					   size2i)
+		   && maxsizei % BITS_PER_UNIT == 0
+		   && offseti % BITS_PER_UNIT == 0
+		   && size2i % BITS_PER_UNIT == 0
+		   && offset2i % BITS_PER_UNIT == 0)
 	    {
 	      pd_data pd;
 	      tree rhs = gimple_assign_rhs1 (def_stmt);