RFR: 8224851: AArch64: fix warnings and errors with Clang and GCC 8.3

[Nick Gasson]

Hi,

Please review this set of fixes to building hotspot with GCC 8.3 or 
Clang 7.0 on AArch64.

Bug: https://bugs.openjdk.java.net/browse/JDK-8224851
Webrev: http://cr.openjdk.java.net/~ngasson/8224851/webrev.0/

Ran jtreg with no new failures.

This first one is with GCC 8.3:

/home/nicgas01/jdk/src/hotspot/cpu/aarch64/frame_aarch64.cpp: In function 'void pf(long unsigned int, long unsigned int, long unsigned int, long unsigned int, long unsigned int)':
/home/nicgas01/jdk/src/hotspot/cpu/aarch64/frame_aarch64.cpp:775:35: error: 'void* memcpy(void*, const void*, size_t)' writing to an object of type 'class RegisterMap' with no trivial copy-assignment; use copy-assignment or copy-initialization instead [-Werror=class-memaccess]
   memcpy(reg_map, &map, sizeof map);
                                   ^

RegisterMap is non-POD because its base class AllocatedObj has virtual
methods, so we need to use copy-assignment rather than memcpy. But
because we're allocating reg_map with os::malloc we ought to use
placement new to properly construct it first. But we can't do that
because RegisterMap inherits from StackObj which disallows new. So I
just put in some casts to void * to silence the warning.

I can't see where `pf' and `internal_pf' are used - perhaps they can be
called manually from the debugger? If no one uses them maybe they should
be deleted?

The remaining warnings / errors are with Clang 7.0.

/home/nicgas01/jdk/src/hotspot/cpu/aarch64/assembler_aarch64.hpp:279:22: error: & has lower precedence than ==; == will be evaluated first [-Werror,-Wparentheses]
    assert_cond(bits & mask == mask);
                     ^~~~~~~~~~~~~~

To preserve the behaviour we should write `bits & (mask == mask)' but I
don't think this was what was intended so I changed it to
`(bits & mask) == mask'.

/home/nicgas01/jdk/src/hotspot/cpu/aarch64/interp_masm_aarch64.hpp:44:25: error: redeclaration of using declaration
  using MacroAssembler::call_VM_leaf_base;
        ~~~~~~~~~~~~~~~~^

This using declaration appears twice in a row.

/home/nicgas01/jdk/src/hotspot/cpu/aarch64/aarch64.ad:13866:80: error: invalid suffix 'D' on floating constant
    __ fcmps(as_FloatRegister(opnd_array(1)->reg(ra_,this,idx1)/* src1 */), 0.0D);
                                                                               ^

The "d" or "D" suffix on floating point literals is not in C++98. I
believe it comes from an extension to C to support decimal floating
point? Anyway it's not necessary here.

/home/nicgas01/jdk/src/hotspot/cpu/aarch64/c1_LIRGenerator_aarch64.cpp:429:66: error: implicit conversion of NULL constant to 'bool' [-Werror,-Wnull-conversion]
  arithmetic_op_fpu(x->op(), reg, left.result(), right.result(), NULL);
  ~~~~~~~~~~~~~~~~~                                              ^~~~
                                                                 false

The NULL here is for the `bool is_strictfp' argument to
LIRGenerator::arithmetic_op_fpu. Changing it to `false' would preserve
the existing behaviour but it seems like it should be `x->is_strictfp()'
to match other platforms.

As a consequence of this we need to handle the lir_{div,mul}_scriptfp
opcodes in LIR_Assembler::arith_op, but these just fall through to the
non-strictfp variants so there should be no behaviour change.

/home/nicgas01/jdk/src/hotspot/cpu/aarch64/c1_LIRAssembler_aarch64.cpp:1074:24: error: '&&' within '||' [-Werror,-Wlogical-op-parentheses]
      if (is_unordered && op->cond() == lir_cond_equal
          ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Added parenthesis to make this explicit. No behaviour change.

/home/nicgas01/jdk/src/hotspot/os_cpu/linux_aarch64/copy_linux_aarch64.s:162:32: error: index must be a multiple of 8 in range [0, 32760].
        prfm    pldl1keep, [s, #-256]
                               ^

The immediate offset in `prfm' gets zero-extended to 64-bits and then
left shifted three places so can only be unsigned. GNU as actually
assembles [s, #-256] the same as [s]:

   0:	f9800000 	prfm	pldl1keep, [x0]

Seems like GNU as ought to report an error here instead. I've replaced
this with `prfum' which has a sign-extended offset.

/home/nicgas01/jdk/src/hotspot/os_cpu/linux_aarch64/atomic_linux_aarch64.hpp:43:39: error: cannot initialize a parameter of type 'char *' with an lvalue of type 'unsigned long'
    return __sync_add_and_fetch(dest, add_value);
                                      ^~~~~~~~~

If the add_and_fetch template is instantiated with I=integer and
D=pointer then we need an explicit cast here.

/home/nicgas01/jdk/src/hotspot/os_cpu/linux_aarch64/os_linux_aarch64.cpp:679:8: error: conflicting types for '_Copy_conjoint_jshorts_atomic'
  void _Copy_conjoint_jshorts_atomic(jshort* from, jshort* to, size_t count) {
       ^

This family of functions is declared with const `from' pointer but in
the definition it is non-const. Made it const everywhere.

/home/nicgas01/jdk/src/hotspot/cpu/aarch64/vm_version_aarch64.cpp:177:13: error: using the result of an assignment as a condition without parentheses [-Werror,-Wparentheses]
      if (p = strchr(buf, ':')) {
          ~~^~~~~~~~~~~~~~~~~~

Put parentheses around the argument. No functional change.

/home/nicgas01/jdk/src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp:2684:17: error: shifting a negative signed value is undefined [-Werror,-Wshift-negative-value]
    offset &= -1<<12;
              ~~^

Rewrote as ~((1<<12) - 1) which matches the masks used in the rest of
the function.

/home/nicgas01/jdk/src/hotspot/os_cpu/linux_aarch64/os_linux_aarch64.cpp:103:20: error: variable 'esp' is uninitialized when used here [-Werror,-Wuninitialized]
  return (address) esp;
                   ^~~
/home/nicgas01/jdk/src/hotspot/os_cpu/linux_aarch64/os_linux_aarch64.cpp:101:21: note: initialize the variable 'esp' to silence this warning
  register void *esp __asm__ (SPELL_REG_SP);
                    ^
                     = nullptr

We could silence the -Wuninitialized warning for this function, but that
doesn't help much because Clang then compiles
os::current_stack_pointer() into:

0000000000000000 <_ZN2os21current_stack_pointerEv>:
       0:	d65f03c0 	ret

Whereas with GCC we get:

0000000000000250 <_ZN2os21current_stack_pointerEv>:
     250:	910003e0 	mov	x0, sp
     254:	d65f03c0 	ret

Added some inline assembly to explicitly move sp into the result #ifdef
__clang__. Same with _get_previous_fp().


Thanks,
Nick