[llvm] [PowerPC] fold i128 equality/inequality compares of two loads into a vectorized compare using vcmpequb.p when Altivec is available (PR #158657)

[zhijian lin via llvm-commits]

================
@@ -35,18 +35,13 @@ define signext i32 @zeroEqualityTest02(ptr %x, ptr %y) {
 define signext i32 @zeroEqualityTest01(ptr %x, ptr %y) {
 ; CHECK-LABEL: zeroEqualityTest01:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    ld 5, 0(3)
-; CHECK-NEXT:    ld 6, 0(4)
-; CHECK-NEXT:    cmpld 5, 6
-; CHECK-NEXT:    bne 0, .LBB1_2
-; CHECK-NEXT:  # %bb.1: # %loadbb1
-; CHECK-NEXT:    ld 5, 8(3)
-; CHECK-NEXT:    ld 4, 8(4)
-; CHECK-NEXT:    li 3, 0
-; CHECK-NEXT:    cmpld 5, 4
-; CHECK-NEXT:    beqlr 0
-; CHECK-NEXT:  .LBB1_2: # %res_block
-; CHECK-NEXT:    li 3, 1
+; CHECK-NEXT:    lxvd2x 34, 0, 4
+; CHECK-NEXT:    lxvd2x 35, 0, 3
+; CHECK-NEXT:    vcmpequb. 2, 3, 2
+; CHECK-NEXT:    mfocrf 3, 2
+; CHECK-NEXT:    rlwinm 3, 3, 25, 31, 31
+; CHECK-NEXT:    cntlzw 3, 3
+; CHECK-NEXT:    srwi 3, 3, 5
----------------
diggerlin wrote:

I consider again, I do not think we can transfer 

```
         rlwinm r3, r3, 25, 31, 31
        cntlzw  r3, r3
        srwi r3, r3, 5
```
   
into 
```
    rlwinm r3, r3, 25, 31, 31
    xori r3,  (value).
```
    
  since 
  
```
      cntlzw  r3, r3
      srwi r3, r3, 5
```

check whether only the bit 31 of r3 is 1 . I do not think we have a single xori instruction or other single instruction to achieve it.
       

https://github.com/llvm/llvm-project/pull/158657