Fix hoisting safe dead implicit-defs

Author: atrosinenko

llvm/lib/CodeGen/MachineLICM.cpp

@@ -554,8 +554,6 @@ void MachineLICMImpl::ProcessMI(MachineInstr *MI, BitVector &RUDefs,
     }
 
     if (MO.isImplicit()) {
-      for (MCRegUnit Unit : TRI->regunits(Reg))
-        RUClobbers.set(Unit);
       if (!MO.isDead())
         // Non-dead implicit def? This cannot be hoisted.
         RuledOut = true;
@@ -582,6 +580,8 @@ void MachineLICMImpl::ProcessMI(MachineInstr *MI, BitVector &RUDefs,
       }
 
       RUDefs.set(Unit);
+      if (MO.isImplicit())
+        RUClobbers.set(Unit);
     }
   }
 

llvm/test/CodeGen/AArch64/mlicm-implicit-defs.mir

@@ -62,15 +62,15 @@ body: |
   ; CHECK-NEXT:   liveins: $x0
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT:   $x12 = COPY killed $x0
+  ; CHECK-NEXT:   $x2 = MOVi64imm 1024, implicit-def dead $x16
   ; CHECK-NEXT:   B %bb.1
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT: bb.1:
   ; CHECK-NEXT:   successors: %bb.1(0x40000000), %bb.2(0x40000000)
-  ; CHECK-NEXT:   liveins: $x12
+  ; CHECK-NEXT:   liveins: $x12, $x2
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT:   $x1 = COPY killed $x12
-  ; CHECK-NEXT:   $x2 = MOVi64imm 1024, implicit-def dead $x16
-  ; CHECK-NEXT:   $x16 = LDRXroX killed $x1, killed $x2, 0, 0
+  ; CHECK-NEXT:   $x16 = LDRXroX killed $x1, $x2, 0, 0
   ; CHECK-NEXT:   $xzr = SUBSXri $x16, 0, 0, implicit-def $nzcv
   ; CHECK-NEXT:   Bcc 1, %bb.1, implicit $nzcv
   ; CHECK-NEXT:   B %bb.2