[llvm] [PowerPC] Implement a more efficient memcmp in cases where the length is known. (PR #158657)

[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
----------------
RolandF77 wrote:

Extra instruction? I think isolating and flipping the bit can just be rlwinm/xori.

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