[aarch64-port-dev ] RFR: Remove mistaken shift in form_address

[Edward Nevill]

Hi,

I came across this while looking at the implicit exception offsets.

I believe the shift removed by the patch below is mistaken. 'byte_offset' is already the offset in bytes so shifting it by scale of the data being loaded is wrong.

Regards,
Ed.

Here is some context

Address MacroAssembler::form_address(Register Rd, Register base, long byte_offset, int shift) {
  if (Address::offset_ok_for_immed(byte_offset, shift))
    // It fits; no need for any heroics
    return Address(base, byte_offset);

  // Don't do anything clever with negative or misaligned offsets
  unsigned mask = (1 << shift) - 1;
  if (byte_offset < 0 || byte_offset & mask) {
    mov(Rd, byte_offset);   <<<<< Here it doesn't apply the shift
    add(Rd, base, Rd);
    return Address(Rd);
  }

  // See if we can do this with two 12-bit offsets
  {
    unsigned long word_offset = byte_offset >> shift;  <<<< and here it assumes it needs to shift right
    unsigned long masked_offset = word_offset & 0xfff000;
    if (Address::offset_ok_for_immed(word_offset - masked_offset)
        && Assembler::operand_valid_for_add_sub_immediate(masked_offset << shift)) {
      add(Rd, base, masked_offset << shift);
      word_offset -= masked_offset;
      return Address(Rd, word_offset << shift);
    }
  }

  // Do it the hard way
  mov(Rd, byte_offset << shift);   <<<<<< but here it shift the byte offset left????
  add(Rd, base, Rd);
  return Address(Rd);
}


--- CUT HERE ---
exporting patch:
# HG changeset patch
# User Edward Nevill edward.nevill at linaro.org
# Date 1395245750 0
#      Wed Mar 19 16:15:50 2014 +0000
# Node ID 9393c177ac9b9407f1f4e58bd662b719b40ded54
# Parent  b56e2e46bfe1de5761fbdaf4fd9b021320ab3a18
Remove mistaken shift in form_address

diff -r b56e2e46bfe1 -r 9393c177ac9b src/cpu/aarch64/vm/macroAssembler_aarch64.cpp
--- a/src/cpu/aarch64/vm/macroAssembler_aarch64.cpp	Wed Mar 19 10:39:35 2014 +0000
+++ b/src/cpu/aarch64/vm/macroAssembler_aarch64.cpp	Wed Mar 19 16:15:50 2014 +0000
@@ -1399,7 +1399,7 @@
   }
 
   // Do it the hard way
-  mov(Rd, byte_offset << shift);
+  mov(Rd, byte_offset);
   add(Rd, base, Rd);
   return Address(Rd);
 }
--- CUT HERE ---