[llvm-bugs] [Bug 30833] New: [ppc] Use cmplwi insead of rlwinm. to compare bool var

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=30833

            Bug ID: 30833
           Summary: [ppc] Use cmplwi insead of rlwinm. to compare bool var
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: PowerPC
          Assignee: unassignedbugs at nondot.org
          Reporter: carrot at google.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Compile the following code with options -m64 -O2

struct A { 
   long V() const { return f4 ? f1: f2; }
   bool IsDone() const { return f3 >= V(); }

    long f1, f2; 
    int f3; 
    bool f4; 
  };  

struct B { 
    bool IsDone() const { return  f6 >= f5.f1; }

    void Next();

    A f5; 
    int f6; 
  };  

extern A qux();
extern B bar();

void B::Next() {
  while (f5.IsDone()) {
    f5 = qux();
  }
}

void foo() {
    B iter = bar();
    while (!iter.IsDone()) {
      iter.Next();
    }   
}

LLVM generates:

        ...
        lwz 4, 112(31)
        lbz 5, 116(31)
        ld 7, 104(31)
        addi 29, 31, 128 
        .p2align        4
.LBB1_2:                                # %while.body
                                        # =>This Loop Header: Depth=1
                                        #     Child Loop BB1_3 Depth 2
        rlwinm. 8, 5, 0, 24, 31         // A
        extsw 8, 4
        isel 9, 7, 3, 2
        cmpd     8, 9
        blt      0, .LBB1_5
        .p2align        4
.LBB1_3:                                # %while.body.i
                                        #   Parent Loop BB1_2 Depth=1
                                        # =>  This Inner Loop Header: Depth=2
        mr 3, 29
        bl _Z3quxv
        nop
        lxvd2x 0, 0, 29
        stxvd2x 0, 0, 30
        ori 2, 2, 0
        ld 3, 144(31)
        std 3, 112(31)
        ori 2, 2, 0
        lbz 5, 116(31)
        ld 3, 96(31)
        ld 7, 104(31)
        lwa 4, 112(31)
        cmplwi   5, 0                   // B
        isel 6, 7, 3, 2
        cmpd     4, 6
        bge 0, .LBB1_3
# BB#4:                                 # %while.cond.backedge.loopexit
                                        #   in Loop: Header=BB1_2 Depth=1
        lwz 6, 120(31)
.LBB1_5:                                # %while.cond.backedge
                                        #   in Loop: Header=BB1_2 Depth=1
        extsw 8, 6
        cmpd     8, 3
        blt      0, .LBB1_2
        ...

Note that instruction A is actually comparing a bool variable loaded from
116(31), it can be replaced with a slightly faster instruction cmplwi, just
like instruction B.

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20161028/b649b46b/attachment.html>