[StackColoring] Fix a debug invariance problem

[bjope]

Summary

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).

[djtodoro]

This looks reasonable to me.

llvm/lib/CodeGen/StackColoring.cpp

717

an early continue at the begging of the loop as:

if (MI.isDebugInstr())
  continue;

?

[bjope]

llvm/lib/CodeGen/StackColoring.cpp

717

Thanks for taking a look (I haven't figured out whom to add as a reviewer yet, but maybe you are signing up as a volounteer)!

And sure, probably cleaner to add such an early continue to show that we ignore debug instructions throughout the analysis. I'll fix that.

[bjope]

Move the check for isDebugInstr() to beginning of the loop.

[djtodoro]

LGTM, thanks!

llvm/lib/CodeGen/StackColoring.cpp

 //===- StackColoring.cpp --------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
for (const MachineBasicBlock *Pred : MBB->predecessors()) {
       BlockBitVecMap::const_iterator I = SeenStartMap.find(Pred);
       if (I != SeenStartMap.end()) {
         BetweenStartEnd |= I->second;
       }
     }
 
     // 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);
         if (Slot < 0)
           continue;
         InterestingSlots.set(Slot);
         if (MI.getOpcode() == TargetOpcode::LIFETIME_START) {
           BetweenStartEnd.set(Slot);
for (MachineInstr &MI : *MBB) {
                                     ? "start"
                                     : "end"));
           LLVM_DEBUG(dbgs() << " marker for slot #" << Slot);
           LLVM_DEBUG(dbgs()
                      << " with allocation: " << Allocation->getName() << "\n");
         }
         Markers.push_back(&MI);
         MarkersFound += 1;
       } else {
         for (const MachineOperand &MO : MI.operands()) {
           if (!MO.isFI())
             continue;
           int Slot = MO.getIndex();
           if (Slot < 0)
             continue;
           if (! BetweenStartEnd.test(Slot)) {
             ConservativeSlots.set(Slot);

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

- { id: 3, name: a4, type: default, offset: 0, size: 88, alignment: 8,
       stack-id: default, callee-saved-register: '', callee-saved-restored: true,
       debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
 body:             |
   bb.0.entry:
     liveins: $edi
 
     ; 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
     LIFETIME_START %stack.0.a1
     %0:gr64 = LEA64r %stack.0.a1, 1, $noreg, 0, $noreg
     LIFETIME_END %stack.0.a1
     %1:gr64 = LEA64r %stack.3.a4, 1, $noreg, 0, $noreg
     LIFETIME_END %stack.3.a4