[PATCH] D48813: [PowerPC] Don't make it as pre-inc candidate if displacement isn't 4's multiple for i64 pre-inc load/store

[Kewen Lin via Phabricator via llvm-commits]

jedilyn created this revision.
jedilyn added reviewers: hfinkel, nemanjai, stefanp.

For the below case, pre-inc prep think it's a good candidate to use pre-inc for the bucket, but 64bit integer load/store update (pre-inc) instruction on Power requires the displacement field should be DS-form (4's multiple). Since it can't satisfy the constraint, we have to do some fix ups later. As below, the original load/stores could be well-form, it makes things worse.

  unsigned long long result = 0;
  unsigned long long foo(char *p, unsigned long long n) {
    for (unsigned long long i = 0; i < n; i++) {
      unsigned long long x1 = *(unsigned long long *)(p - 50000 + i);
      unsigned long long x2 = *(unsigned long long *)(p - 61024 + i);
      unsigned long long x3 = *(unsigned long long *)(p - 62048 + i);
      unsigned long long x4 = *(unsigned long long *)(p - 64096 + i);
      result *= x1 * x2 * x3 * x4;
    }
    return result;
  }

The current instruction sequence:

  .LBB0_2:                   
        addi 4, 5, -11023
        addi 7, 5, 1
        addi 8, 5, -12047
        addi 5, 5, -14095
        ld 9, 0(7)
        ld 4, 0(4)
        ld 8, 0(8)
        ld 5, 0(5)
        mulld 4, 4, 9
        mulld 4, 4, 8
        mulld 4, 4, 5
        mr 5, 7
        mulld 3, 4, 3
        bdnz .LBB0_2

With the proposed fix:

  .LBB0_2:    
        ld 4, 14096(5)
        ld 7, 3072(5)
        ld 8, 2048(5)
        ld 9, 0(5)
        addi 5, 5, 1
        mulld 4, 7, 4
        mulld 4, 4, 8
        mulld 4, 4, 9
        mulld 3, 4, 3
        bdnz .LBB0_2

For i64 loads/stores, the proposed fix is to check whether the displacement fits in a 16-bit signed field but isn't a multiple of 4, if so we don't make it as candidate any more.


Repository:
  rL LLVM

https://reviews.llvm.org/D48813

Files:
  llvm/lib/Target/PowerPC/PPCLoopPreIncPrep.cpp
  llvm/test/CodeGen/PowerPC/preincprep-i64-check.ll

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D48813.153661.patch
Type: text/x-patch
Size: 6151 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20180702/537ff1c3/attachment.bin>