[StackColoring] Fix a debug invariance problem

Ignore dbg instructions when collecting stack slot markers. This is
to make sure the coloring is invariant regarding presence of dbg
instructions (even in cases when the dbg instructions might be
badly placed in the input).

Differential Revision: https://reviews.llvm.org/D109758

Author: bjope

llvm/lib/CodeGen/StackColoring.cpp

@@ -687,6 +687,8 @@ unsigned StackColoring::collectMarkers(unsigned NumSlot) {
 
     // Walk the instructions in the block to look for start/end ops.
     for (MachineInstr &MI : *MBB) {
+      if (MI.isDebugInstr())
+        continue;
       if (MI.getOpcode() == TargetOpcode::LIFETIME_START ||
           MI.getOpcode() == TargetOpcode::LIFETIME_END) {
         int Slot = getStartOrEndSlot(MI);

llvm/test/CodeGen/X86/StackColoring-dbg-invariance.mir

@@ -74,9 +74,9 @@ body:             |
 
     ; CHECK-LABEL: name: test_1
     ; CHECK: liveins: $edi
-    ; CHECK: DBG_VALUE %stack.1.a4, $noreg, !9, !DIExpression(), debug-location !11
+    ; CHECK: DBG_VALUE %stack.0.a1, $noreg, !9, !DIExpression(), debug-location !11
     ; CHECK: [[LEA64r:%[0-9]+]]:gr64 = LEA64r %stack.0.a1, 1, $noreg, 0, $noreg
-    ; CHECK: [[LEA64r1:%[0-9]+]]:gr64 = LEA64r %stack.1.a4, 1, $noreg, 0, $noreg
+    ; CHECK: [[LEA64r1:%[0-9]+]]:gr64 = LEA64r %stack.0.a1, 1, $noreg, 0, $noreg
     ; CHECK: RET 0
     DBG_VALUE %stack.3.a4, $noreg, !9, !DIExpression(), debug-location !11
     LIFETIME_START %stack.3.a4