llvm-svn: 19656

X86/reg-pressure.ll again, and allows us to do nice things in other cases.
For example, we now codegen this sort of thing:

int %loadload(int *%X, int* %Y) {
  %Z = load int* %Y
  %Y = load int* %X      ;; load between %Z and store
  %Q = add int %Z, 1
  store int %Q, int* %Y
  ret int %Y
}

Into this:

loadload:
        mov %EAX, DWORD PTR [%ESP + 4]
        mov %EAX, DWORD PTR [%EAX]
        mov %ECX, DWORD PTR [%ESP + 8]
        inc DWORD PTR [%ECX]
        ret

where we weren't able to form the 'inc [mem]' before.  This also lets the
instruction selector emit loads in any order it wants to, which can be good
for register pressure as well.

llvm-svn: 19644

llvm-svn: 19642

the basic block that uses them if possible.  This is a big win on X86, as it
lets us fold the argument loads into instructions and reduce register pressure
(by not loading all of the arguments in the entry block).

For this (contrived to show the optimization) testcase:

int %argtest(int %A, int %B) {
        %X = sub int 12345, %A
        br label %L
L:
        %Y = add int %X, %B
        ret int %Y
}

we used to produce:

argtest:
        mov %ECX, DWORD PTR [%ESP + 4]
        mov %EAX, 12345
        sub %EAX, %ECX
        mov %EDX, DWORD PTR [%ESP + 8]
.LBBargtest_1:  # L
        add %EAX, %EDX
        ret


now we produce:

argtest:
        mov %EAX, 12345
        sub %EAX, DWORD PTR [%ESP + 4]
.LBBargtest_1:  # L
        add %EAX, DWORD PTR [%ESP + 8]
        ret

This also fixes the FIXME in the code.

BTW, this occurs in real code.  164.gzip shrinks from 8623 to 8608 lines of
.s file.  The stack frame in huft_build shrinks from 1644->1628 bytes,
inflate_codes shrinks from 116->108 bytes, and inflate_block from 2620->2612,
due to fewer spills.

Take that alkis. :-)

llvm-svn: 19639

llvm-svn: 19635

llvm-svn: 19612

llvm-svn: 19595

llvm-svn: 19582

llvm-svn: 19579

llvm-svn: 19568

stores/loads.

llvm-svn: 19562

llvm-svn: 19535

llvm-svn: 19531

llvm-svn: 19528

llvm-svn: 19498

same for PHI nodes.

llvm-svn: 19484

llvm-svn: 19463

llvm-svn: 19409

llvm-svn: 19407

llvm-svn: 19404

llvm-svn: 19384

llvm-svn: 19374

llvm-svn: 19369

int GEP indices on 64-bit archs.

llvm-svn: 19354

llvm-svn: 19349

of the code for lowering from LLVM code to a SelectionDAG.

llvm-svn: 19331