[ppc] redundant zero extension when returning bool value

[Quuxplusone]

Bugzilla Link	PR32442
Status	CONFIRMED
Importance	P enhancement
Reported by	Carrot (carrot@google.com)
Reported on	2017-03-27 14:45:04 -0700
Last modified on	2017-04-18 00:44:00 -0700
Version	trunk
Hardware	PC Linux
CC	hfinkel@anl.gov, inouehrs@jp.ibm.com, kit.barton@gmail.com, llvm-bugs@lists.llvm.org
Fixed by commit(s)
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Compile the following code with options -m64 -O2 -mvsx -mcpu=power8

bool foo(int i, int* p) {
  if (i==0)
    return false;

  *p = i;
  return true;
}

LLVM generates:

_Z3fooiPi:                              # @_Z3fooiPi
.Lfunc_begin0:
# BB#0:                                 # %entry
        cmplwi   3, 0
        beq      0, .LBB0_2
# BB#1:                                 # %if.end
        stw 3, 0(4)
        li 3, 1
        clrldi   3, 3, 32           // redundant
        blr
.LBB0_2:
        li 3, 0
        clrldi   3, 3, 32           // redundant
        blr

The problem is when PPCBoolRetToInt.cpp converts the old the old cmp/isel
behavior into today's integer operation, it uses  i32 type, on ppc64, it needs
to be zero extended to 64bit before return. We should use i64 on ppc64 and i32
on ppc32.

[Quuxplusone]

The following patch (under review in Phabricator) resolves this issue.
https://reviews.llvm.org/D31319

Generated code with the patch:

_Z3fooiPi:                              # @_Z3fooiPi
.Lfunc_begin0:
# BB#0:                                 # %entry
    cmplwi   3, 0
    beq  0, .LBB0_2
# BB#1:                                 # %if.end
    stw 3, 0(4)
    li 3, 1
    blr
.LBB0_2:
    li 3, 0
    blr