RFR: 8255838: Use 32-bit immediate movslq in macro assembler if 64-bit value fits in 32 bits on x86_64

[Jorn Vernee]

Currently, Macro::Assembler(Address dst, intprt_t src) on x64 uses an intermediate scratch register to store the 64-bit immediate.

void MacroAssembler::movptr(Address dst, intptr_t src) {
  mov64(rscratch1, src);
  movq(dst, rscratch1);
}

But, if the value fits into 32-bits, we can also explicitly use the 32-bit immediate overload, which saves an instruction and a register use, by using movslq/movabs instead (sig extended move).

This ends up saving about 90k instructions on hello world. It also reduces the size of the interpreter by about 4k.

Special thanks to Claes for prior discussion and help with testing.

Testing: tier1-3, local startup profiling

-------------

Commit messages:
 - Explicitly convert intptr_t to int32_t to use movslq on 64 bit platforms if possible

Changes: https://git.openjdk.java.net/jdk/pull/1038/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1038&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255838
  Stats: 6 lines in 1 file changed: 4 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1038.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1038/head:pull/1038

PR: https://git.openjdk.java.net/jdk/pull/1038