gdb/gdb-rhbz1420304-s390x-24of35.patch

commit f236533e3c6a2693bea879b2a4d24d1229864ac9
Author: Andreas Arnez <arnez@linux.vnet.ibm.com>
Date:   Tue Jun 13 15:20:31 2017 +0200

    read/write_pieced_value: Remove unnecessary variable copies
    
    In read_pieced_value's main loop, the variables `dest_offset_bits' and
    `source_offset_bits' are basically just copies of `offset' and
    `bits_to_skip', respectively.  In write_pieced_value the copies are
    reversed.  This is not very helpful when trying to keep the logic between
    these functions in sync.  Since the copies are unnecessary, this patch
    just removes them.
    
    gdb/ChangeLog:
    
            * dwarf2loc.c (read_pieced_value): Remove unnecessary variables
            dest_offset_bits and source_offset_bits.
            (write_pieced_value): Likewise.

### a/gdb/ChangeLog
### b/gdb/ChangeLog
## -1,5 +1,11 @@
 2017-06-13  Andreas Arnez  <arnez@linux.vnet.ibm.com>
 
+	* dwarf2loc.c (read_pieced_value): Remove unnecessary variables
+	dest_offset_bits and source_offset_bits.
+	(write_pieced_value): Likewise.
+
+2017-06-13  Andreas Arnez  <arnez@linux.vnet.ibm.com>
+
 	* dwarf2loc.c (read_pieced_value): Respect the piece offset, as
 	given by DW_OP_bit_piece.
 	(write_pieced_value): Likewise.
--- a/gdb/dwarf2loc.c
+++ b/gdb/dwarf2loc.c
@@ -1790,25 +1790,16 @@ read_pieced_value (struct value *v)
   else
     max_offset = 8 * TYPE_LENGTH (value_type (v));
 
-  for (i = 0; i < c->n_pieces && offset < max_offset; i++)
+  /* Advance to the first non-skipped piece.  */
+  for (i = 0; i < c->n_pieces && bits_to_skip >= c->pieces[i].size; i++)
+    bits_to_skip -= c->pieces[i].size;
+
+  for (; i < c->n_pieces && offset < max_offset; i++)
     {
       struct dwarf_expr_piece *p = &c->pieces[i];
       size_t this_size, this_size_bits;
-      long dest_offset_bits, source_offset_bits;
-
-      /* Compute size, source, and destination offsets for copying, in
-	 bits.  */
-      this_size_bits = p->size;
-      if (bits_to_skip > 0 && bits_to_skip >= this_size_bits)
-	{
-	  bits_to_skip -= this_size_bits;
-	  continue;
-	}
-      source_offset_bits = bits_to_skip;
-      this_size_bits -= bits_to_skip;
-      bits_to_skip = 0;
-      dest_offset_bits = offset;
 
+      this_size_bits = p->size - bits_to_skip;
       if (this_size_bits > max_offset - offset)
 	this_size_bits = max_offset - offset;
 
@@ -1827,16 +1818,16 @@ read_pieced_value (struct value *v)
 		&& p->offset + p->size < reg_bits)
 	      {
 		/* Big-endian, and we want less than full size.  */
-		source_offset_bits += reg_bits - (p->offset + p->size);
+		bits_to_skip += reg_bits - (p->offset + p->size);
 	      }
 	    else
-	      source_offset_bits += p->offset;
+	      bits_to_skip += p->offset;
 
-	    this_size = bits_to_bytes (source_offset_bits, this_size_bits);
+	    this_size = bits_to_bytes (bits_to_skip, this_size_bits);
 	    buffer.reserve (this_size);
 
 	    if (!get_frame_register_bytes (frame, gdb_regnum,
-					   source_offset_bits / 8,
+					   bits_to_skip / 8,
 					   this_size, buffer.data (),
 					   &optim, &unavail))
 	      {
@@ -1846,24 +1837,23 @@ read_pieced_value (struct value *v)
 		  mark_value_bits_unavailable (v, offset, this_size_bits);
 		break;
 	      }
-
-	    copy_bitwise (contents, dest_offset_bits,
-			  buffer.data (), source_offset_bits % 8,
+	    copy_bitwise (contents, offset,
+			  buffer.data (), bits_to_skip % 8,
 			  this_size_bits, bits_big_endian);
 	  }
 	  break;
 
 	case DWARF_VALUE_MEMORY:
-	  source_offset_bits += p->offset;
-	  this_size = bits_to_bytes (source_offset_bits, this_size_bits);
+	  bits_to_skip += p->offset;
+	  this_size = bits_to_bytes (bits_to_skip, this_size_bits);
 	  buffer.reserve (this_size);
 
 	  read_value_memory (v, offset,
 			     p->v.mem.in_stack_memory,
-			     p->v.mem.addr + source_offset_bits / 8,
+			     p->v.mem.addr + bits_to_skip / 8,
 			     buffer.data (), this_size);
-	  copy_bitwise (contents, dest_offset_bits,
-			buffer.data (), source_offset_bits % 8,
+	  copy_bitwise (contents, offset,
+			buffer.data (), bits_to_skip % 8,
 			this_size_bits, bits_big_endian);
 	  break;
 
@@ -1880,14 +1870,13 @@ read_pieced_value (struct value *v)
 
 	    /* Piece is anchored at least significant bit end.  */
 	    if (gdbarch_byte_order (objfile_gdbarch) == BFD_ENDIAN_BIG)
-	      source_offset_bits += (stack_value_size_bits
-				     - p->offset - p->size);
+	      bits_to_skip += stack_value_size_bits - p->offset - p->size;
 	    else
-	      source_offset_bits += p->offset;
+	      bits_to_skip += p->offset;
 
-	    copy_bitwise (contents, dest_offset_bits,
+	    copy_bitwise (contents, offset,
 			  value_contents_all (p->v.value),
-			  source_offset_bits,
+			  bits_to_skip,
 			  this_size_bits, bits_big_endian);
 	  }
 	  break;
@@ -1898,14 +1887,14 @@ read_pieced_value (struct value *v)
 	    size_t n = this_size_bits;
 
 	    /* Cut off at the end of the implicit value.  */
-	    source_offset_bits += p->offset;
-	    if (source_offset_bits >= literal_size_bits)
+	    bits_to_skip += p->offset;
+	    if (bits_to_skip >= literal_size_bits)
 	      break;
-	    if (n > literal_size_bits - source_offset_bits)
-	      n = literal_size_bits - source_offset_bits;
+	    if (n > literal_size_bits - bits_to_skip)
+	      n = literal_size_bits - bits_to_skip;
 
-	    copy_bitwise (contents, dest_offset_bits,
-			  p->v.literal.data, source_offset_bits,
+	    copy_bitwise (contents, offset,
+			  p->v.literal.data, bits_to_skip,
 			  n, bits_big_endian);
 	  }
 	  break;
@@ -1924,6 +1913,7 @@ read_pieced_value (struct value *v)
 	}
 
       offset += this_size_bits;
+      bits_to_skip = 0;
     }
 }
 
@@ -1959,23 +1949,16 @@ write_pieced_value (struct value *to, struct value *from)
   else
     max_offset = 8 * TYPE_LENGTH (value_type (to));
 
-  for (i = 0; i < c->n_pieces && offset < max_offset; i++)
+  /* Advance to the first non-skipped piece.  */
+  for (i = 0; i < c->n_pieces && bits_to_skip >= c->pieces[i].size; i++)
+    bits_to_skip -= c->pieces[i].size;
+
+  for (; i < c->n_pieces && offset < max_offset; i++)
     {
       struct dwarf_expr_piece *p = &c->pieces[i];
       size_t this_size_bits, this_size;
-      long dest_offset_bits, source_offset_bits;
-
-      this_size_bits = p->size;
-      if (bits_to_skip > 0 && bits_to_skip >= this_size_bits)
-	{
-	  bits_to_skip -= this_size_bits;
-	  continue;
-	}
-      dest_offset_bits = bits_to_skip;
-      this_size_bits -= bits_to_skip;
-      bits_to_skip = 0;
-      source_offset_bits = offset;
 
+      this_size_bits = p->size - bits_to_skip;
       if (this_size_bits > max_offset - offset)
 	this_size_bits = max_offset - offset;
 
@@ -1992,22 +1975,22 @@ write_pieced_value (struct value *to, struct value *from)
 		&& p->offset + p->size < reg_bits)
 	      {
 		/* Big-endian, and we want less than full size.  */
-		dest_offset_bits += reg_bits - (p->offset + p->size);
+		bits_to_skip += reg_bits - (p->offset + p->size);
 	      }
 	    else
-	      dest_offset_bits += p->offset;
+	      bits_to_skip += p->offset;
 
-	    this_size = bits_to_bytes (dest_offset_bits, this_size_bits);
+	    this_size = bits_to_bytes (bits_to_skip, this_size_bits);
 	    buffer.reserve (this_size);
 
-	    if (dest_offset_bits % 8 != 0 || this_size_bits % 8 != 0)
+	    if (bits_to_skip % 8 != 0 || this_size_bits % 8 != 0)
 	      {
 		/* Data is copied non-byte-aligned into the register.
 		   Need some bits from original register value.  */
 		int optim, unavail;
 
 		if (!get_frame_register_bytes (frame, gdb_regnum,
-					       dest_offset_bits / 8,
+					       bits_to_skip / 8,
 					       this_size, buffer.data (),
 					       &optim, &unavail))
 		  {
@@ -2024,34 +2007,34 @@ write_pieced_value (struct value *to, struct value *from)
 		  }
 	      }
 
-	    copy_bitwise (buffer.data (), dest_offset_bits % 8,
-			  contents, source_offset_bits,
+	    copy_bitwise (buffer.data (), bits_to_skip % 8,
+			  contents, offset,
 			  this_size_bits, bits_big_endian);
 	    put_frame_register_bytes (frame, gdb_regnum,
-				      dest_offset_bits / 8,
+				      bits_to_skip / 8,
 				      this_size, buffer.data ());
 	  }
 	  break;
 	case DWARF_VALUE_MEMORY:
 	  {
-	    dest_offset_bits += p->offset;
+	    bits_to_skip += p->offset;
 
-	    CORE_ADDR start_addr = p->v.mem.addr + dest_offset_bits / 8;
+	    CORE_ADDR start_addr = p->v.mem.addr + bits_to_skip / 8;
 
-	    if (dest_offset_bits % 8 == 0 && this_size_bits % 8 == 0
-		&& source_offset_bits % 8 == 0)
+	    if (bits_to_skip % 8 == 0 && this_size_bits % 8 == 0
+		&& offset % 8 == 0)
 	      {
 		/* Everything is byte-aligned; no buffer needed.  */
 		write_memory (start_addr,
-			      contents + source_offset_bits / 8,
+			      contents + offset / 8,
 			      this_size_bits / 8);
 		break;
 	      }
 
-	    this_size = bits_to_bytes (dest_offset_bits, this_size_bits);
+	    this_size = bits_to_bytes (bits_to_skip, this_size_bits);
 	    buffer.reserve (this_size);
 
-	    if (dest_offset_bits % 8 != 0 || this_size_bits % 8 != 0)
+	    if (bits_to_skip % 8 != 0 || this_size_bits % 8 != 0)
 	      {
 		if (this_size <= 8)
 		  {
@@ -2068,8 +2051,8 @@ write_pieced_value (struct value *to, struct value *from)
 		  }
 	      }
 
-	    copy_bitwise (buffer.data (), dest_offset_bits % 8,
-			  contents, source_offset_bits,
+	    copy_bitwise (buffer.data (), bits_to_skip % 8,
+			  contents, offset,
 			  this_size_bits, bits_big_endian);
 	    write_memory (start_addr, buffer.data (), this_size);
 	  }
@@ -2079,6 +2062,7 @@ write_pieced_value (struct value *to, struct value *from)
 	  break;
 	}
       offset += this_size_bits;
+      bits_to_skip = 0;
     }
 }