[DebugInstrRef] Parse debug instruction-references from/to MIR

This patch defines the MIR format for debug instruction references: it's an
integer trailing an instruction, marked out by "debug-instr-number", much
like how "debug-location" identifies the DebugLoc metadata of an
instruction. The instruction number is stored directly in a MachineInstr.

Actually referring to an instruction comes in a later patch, but is done
using one of these instruction numbers.

I've added a round-trip test and two verifier checks: that we don't label
meta-instructions as generating values, and that there are no duplicates.

Differential Revision: https://reviews.llvm.org/D85746

1 files changed, 20 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineVerifier.cpp b/llvm/lib/CodeGen/MachineVerifier.cpp
index 31c6ab8..5c22673 100644
--- a/llvm/lib/CodeGen/MachineVerifier.cpp
+++ b/llvm/lib/CodeGen/MachineVerifier.cpp
@@ -1556,6 +1556,11 @@ void MachineVerifier::visitMachineInstrBefore(const MachineInstr *MI) {
     if (!MI->getDebugLoc())
       report("Missing DebugLoc for debug instruction", MI);
 
+  // Meta instructions should never be the subject of debug value tracking,
+  // they don't create a value in the output program at all.
+  if (MI->isMetaInstruction() && MI->peekDebugInstrNum())
+    report("Metadata instruction should not have a value tracking number", MI);
+
   // Check the MachineMemOperands for basic consistency.
   for (MachineMemOperand *Op : MI->memoperands()) {
     if (Op->isLoad() && !MI->mayLoad())
@@ -2519,6 +2524,21 @@ void MachineVerifier::visitMachineFunctionAfter() {
   for (auto CSInfo : MF->getCallSitesInfo())
     if (!CSInfo.first->isCall())
       report("Call site info referencing instruction that is not call", MF);
+
+  // If there's debug-info, check that we don't have any duplicate value
+  // tracking numbers.
+  if (MF->getFunction().getSubprogram()) {
+    DenseSet<unsigned> SeenNumbers;
+    for (auto &MBB : *MF) {
+      for (auto &MI : MBB) {
+        if (auto Num = MI.peekDebugInstrNum()) {
+          auto Result = SeenNumbers.insert((unsigned)Num);
+          if (!Result.second)
+            report("Instruction has a duplicated value tracking number", &MI);
+        }
+      }
+    }
+  }
 }
 
 void MachineVerifier::verifyLiveVariables() {