[AArch64][Falkor] Ignore SP based loads in HW prefetch fixups.

[mcrosier]

LGTM.

llvm/trunk/lib/Target/AArch64/AArch64FalkorHWPFFix.cpp

static Optional<LoadInfo> getLoadInfo(const MachineInstr &MI) {
   case AArch64::LDPXpre:
     DestRegIdx = 1;
     BaseRegIdx = 3;
     OffsetIdx = 4;
     IsPrePost = true;
     break;
   }
 
+  // Loads from the stack pointer don't get prefetched.
+  unsigned BaseReg = MI.getOperand(BaseRegIdx).getReg();
+  if (BaseReg == AArch64::SP || BaseReg == AArch64::WSP)
+    return None;
+
   LoadInfo LI;
   LI.DestReg = DestRegIdx == -1 ? 0 : MI.getOperand(DestRegIdx).getReg();
-  LI.BaseReg = MI.getOperand(BaseRegIdx).getReg();
+  LI.BaseReg = BaseReg;
   LI.BaseRegIdx = BaseRegIdx;
   LI.OffsetOpnd = OffsetIdx == -1 ? nullptr : &MI.getOperand(OffsetIdx);
   LI.IsPrePost = IsPrePost;
   return LI;
 }
 
 static Optional<unsigned> getTag(const TargetRegisterInfo *TRI,
                                  const MachineInstr &MI, const LoadInfo &LI) {

llvm/trunk/test/CodeGen/AArch64/falkor-hwpf-fix.mir

bb.0:
 
     %w0 = SUBWri %w0, 1, 0
     %wzr = SUBSWri %w0, 0, 0, implicit-def %nzcv
     Bcc 9, %bb.0, implicit %nzcv
 
   bb.1:
     RET_ReallyLR
 ...
+---
+# Check that we treat sp based loads as non-prefetching.
+
+# CHECK-LABEL: name: hwpf_spbase
+# CHECK-NOT: ORRXrs %xzr
+# CHECK: LDRWui %x15
+# CHECK: LDRWui %sp
+name:            hwpf_spbase
+tracksRegLiveness: true
+body: |
+  bb.0:
+    liveins: %w0, %x15
+
+    %w1 = LDRWui %x15, 0 :: ("aarch64-strided-access" load 4)
+    %w17 = LDRWui %sp, 0
+
+    %w0 = SUBWri %w0, 1, 0
+    %wzr = SUBSWri %w0, 0, 0, implicit-def %nzcv
+    Bcc 9, %bb.0, implicit %nzcv
+
+  bb.1:
+    RET_ReallyLR
+...