[MachineSink] Some more preserving of debug location when rematerialising an instruction to replace a COPY

[momchil-velikov]

Somewhet similar to ef9bcac
([MachineSink][AArch64] Preserve debug location when rematerialising
an instruction to replace a COPY (#72685))
reuse the debug location of the COPY, iff the rematerialised instruction
did not have a location.

Fixes a regression in DebugInfo/AArch64/constant-dbgloc.ll after enabling sinj-and-fold.

[llvmbot]

@llvm/pr-subscribers-debuginfo

@llvm/pr-subscribers-backend-aarch64

Author: Momchil Velikov (momchil-velikov)

Changes

Somewhet similar to ef9bcac
([MachineSink][AArch64] Preserve debug location when rematerialising
an instruction to replace a COPY (#72685))
reuse the debug location of the COPY, iff the rematerialised instruction
did not have a location.

---

Full diff: https://github.com/llvm/llvm-project/pull/73155.diff

3 Files Affected:

• (modified) llvm/lib/CodeGen/MachineSink.cpp (+3-1)
• (modified) llvm/lib/Target/AArch64/AArch64TargetMachine.cpp (+1-1)
• (modified) llvm/test/CodeGen/AArch64/sink-and-fold.ll (+1-1)

diff --git a/llvm/lib/CodeGen/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
index 48f5a21406f08a8..83d775055dfd733 100644
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -506,7 +506,7 @@ bool MachineSinking::PerformSinkAndFold(MachineInstr &MI,
     MRI->clearKillFlags(UsedRegB);
 
   for (auto &[SinkDst, MaybeAM] : SinkInto) {
-    [[maybe_unused]] MachineInstr *New = nullptr;
+    MachineInstr *New = nullptr;
     LLVM_DEBUG(dbgs() << "Sinking copy of"; MI.dump(); dbgs() << "into";
                SinkDst->dump());
     if (SinkDst->isCopy()) {
@@ -525,6 +525,8 @@ bool MachineSinking::PerformSinkAndFold(MachineInstr &MI,
       Register DstReg = SinkDst->getOperand(0).getReg();
       TII->reMaterialize(*SinkDst->getParent(), InsertPt, DstReg, 0, MI, *TRI);
       New = &*std::prev(InsertPt);
+      if (!New->getDebugLoc())
+        New->setDebugLoc(SinkDst->getDebugLoc());
     } else {
       // Fold instruction into the addressing mode of a memory instruction.
       New = TII->emitLdStWithAddr(*SinkDst, MaybeAM);
diff --git a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
index d418a297218eb06..036719be06d83f1 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
@@ -200,7 +200,7 @@ static cl::opt<bool> EnableGISelLoadStoreOptPostLegal(
 static cl::opt<bool>
     EnableSinkFold("aarch64-enable-sink-fold",
                    cl::desc("Enable sinking and folding of instruction copies"),
-                   cl::init(false), cl::Hidden);
+                   cl::init(true), cl::Hidden);
 
 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAArch64Target() {
   // Register the target.
diff --git a/llvm/test/CodeGen/AArch64/sink-and-fold.ll b/llvm/test/CodeGen/AArch64/sink-and-fold.ll
index 632fdb391053121..52007221e12a7b5 100644
--- a/llvm/test/CodeGen/AArch64/sink-and-fold.ll
+++ b/llvm/test/CodeGen/AArch64/sink-and-fold.ll
@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc -aarch64-enable-sink-fold=true < %s | FileCheck %s
+; RUN: llc < %s | FileCheck %s
 target triple = "aarch64-linux"
 
 declare i32 @use(...)

[davemgreen]

Can you add the sinkand-fold flag temporarily to DebugInfo/AArch64/constant-dbgloc.ll, to show it still working? It can be removed again later but helps show this is tested.

[davemgreen]

Thanks. LGTM