[GIsel][CombinerHelper] Don't consider debug insts in dominance queri…

…es [3/10]

Summary:
This fixes several issues where the presence of debug instructions could
disable certain combines, due to dominance queries finding uses/defs that
don't actually exist.

Reviewers: dsanders, fhahn, paquette, aemerson

Subscribers: hiraditya, arphaman, aprantl, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78253

llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h

@@ -77,15 +77,15 @@ class CombinerHelper {
 
   /// Returns true if \p DefMI precedes \p UseMI or they are the same
   /// instruction. Both must be in the same basic block.
-  bool isPredecessor(MachineInstr &DefMI, MachineInstr &UseMI);
+  bool isPredecessor(const MachineInstr &DefMI, const MachineInstr &UseMI);
 
   /// Returns true if \p DefMI dominates \p UseMI. By definition an
   /// instruction dominates itself.
   ///
   /// If we haven't been provided with a MachineDominatorTree during
   /// construction, this function returns a conservative result that tracks just
   /// a single basic block.
-  bool dominates(MachineInstr &DefMI, MachineInstr &UseMI);
+  bool dominates(const MachineInstr &DefMI, const MachineInstr &UseMI);
 
   /// If \p MI is extend that consumes the result of a load, try to combine it.
   /// Returns true if MI changed.

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

@@ -429,7 +429,7 @@ bool CombinerHelper::matchCombineExtendingLoads(MachineInstr &MI,
                                        ? TargetOpcode::G_SEXT
                                        : TargetOpcode::G_ZEXT;
   Preferred = {LLT(), PreferredOpcode, nullptr};
-  for (auto &UseMI : MRI.use_instructions(LoadValue.getReg())) {
+  for (auto &UseMI : MRI.use_nodbg_instructions(LoadValue.getReg())) {
     if (UseMI.getOpcode() == TargetOpcode::G_SEXT ||
         UseMI.getOpcode() == TargetOpcode::G_ZEXT ||
         UseMI.getOpcode() == TargetOpcode::G_ANYEXT) {
@@ -560,7 +560,10 @@ void CombinerHelper::applyCombineExtendingLoads(MachineInstr &MI,
   Observer.changedInstr(MI);
 }
 
-bool CombinerHelper::isPredecessor(MachineInstr &DefMI, MachineInstr &UseMI) {
+bool CombinerHelper::isPredecessor(const MachineInstr &DefMI,
+                                   const MachineInstr &UseMI) {
+  assert(!DefMI.isDebugInstr() && !UseMI.isDebugInstr() &&
+         "shouldn't consider debug uses");
   assert(DefMI.getParent() == UseMI.getParent());
   if (&DefMI == &UseMI)
     return false;
@@ -573,7 +576,10 @@ bool CombinerHelper::isPredecessor(MachineInstr &DefMI, MachineInstr &UseMI) {
   llvm_unreachable("Block must contain instructions");
 }
 
-bool CombinerHelper::dominates(MachineInstr &DefMI, MachineInstr &UseMI) {
+bool CombinerHelper::dominates(const MachineInstr &DefMI,
+                               const MachineInstr &UseMI) {
+  assert(!DefMI.isDebugInstr() && !UseMI.isDebugInstr() &&
+         "shouldn't consider debug uses");
   if (MDT)
     return MDT->dominates(&DefMI, &UseMI);
   else if (DefMI.getParent() != UseMI.getParent())
@@ -600,7 +606,7 @@ bool CombinerHelper::findPostIndexCandidate(MachineInstr &MI, Register &Addr,
 
   LLVM_DEBUG(dbgs() << "Searching for post-indexing opportunity for: " << MI);
 
-  for (auto &Use : MRI.use_instructions(Base)) {
+  for (auto &Use : MRI.use_nodbg_instructions(Base)) {
     if (Use.getOpcode() != TargetOpcode::G_PTR_ADD)
       continue;
 
@@ -627,7 +633,8 @@ bool CombinerHelper::findPostIndexCandidate(MachineInstr &MI, Register &Addr,
     // forming an indexed one.
 
     bool MemOpDominatesAddrUses = true;
-    for (auto &PtrAddUse : MRI.use_instructions(Use.getOperand(0).getReg())) {
+    for (auto &PtrAddUse :
+         MRI.use_nodbg_instructions(Use.getOperand(0).getReg())) {
       if (!dominates(MI, PtrAddUse)) {
         MemOpDominatesAddrUses = false;
         break;
@@ -700,7 +707,7 @@ bool CombinerHelper::findPreIndexCandidate(MachineInstr &MI, Register &Addr,
   // FIXME: check whether all uses of the base pointer are constant PtrAdds.
   // That might allow us to end base's liveness here by adjusting the constant.
 
-  for (auto &UseMI : MRI.use_instructions(Addr)) {
+  for (auto &UseMI : MRI.use_nodbg_instructions(Addr)) {
     if (!dominates(MI, UseMI)) {
       LLVM_DEBUG(dbgs() << "    Skipping, does not dominate all addr uses.");
       return false;

llvm/test/CodeGen/AArch64/GlobalISel/combiner-load-store-indexing.ll

@@ -1,4 +1,4 @@
-; RUN: llc -mtriple=arm64-apple-ios -global-isel -global-isel-abort=1 -verify-machineinstrs -stop-after=aarch64-prelegalizer-combiner -force-legal-indexing %s -o - | FileCheck %s
+; RUN: llc -debugify-and-strip-all-safe -mtriple=arm64-apple-ios -global-isel -global-isel-abort=1 -verify-machineinstrs -stop-after=aarch64-prelegalizer-combiner -force-legal-indexing %s -o - | FileCheck %s
 
 define i8* @test_simple_load_pre(i8* %ptr) {
 ; CHECK-LABEL: name: test_simple_load_pre