Add pass to strip debug info from MIR

Summary:
Removes:
* All LLVM-IR level debug info using StripDebugInfo()
* All debugify metadata
* 'Debug Info Version' module flag
* All (valid*) DEBUG_VALUE MachineInstrs
* All DebugLocs from MachineInstrs

This is a more complete solution than the previous MIRPrinter
option that just causes it to neglect to print debug-locations.

* The qualifier 'valid' is used here because AArch64 emits
  an invalid one and tests depend on it

Reviewers: vsk, aprantl, bogner

Subscribers: mgorny, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77747

1 files changed, 112 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineStripDebug.cpp b/llvm/lib/CodeGen/MachineStripDebug.cpp
new file mode 100644
index 0000000..0129718
--- /dev/null
+++ b/llvm/lib/CodeGen/MachineStripDebug.cpp
@@ -0,0 +1,112 @@
+//===- MachineStripDebug.cpp - Strip debug info ---------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file This removes debug info from everything. It can be used to ensure
+/// tests can be debugified without affecting the output MIR.
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/IR/DebugInfo.h"
+#include "llvm/InitializePasses.h"
+
+#define DEBUG_TYPE "mir-strip-debug"
+
+using namespace llvm;
+
+namespace {
+
+struct StripDebugMachineModule : public ModulePass {
+  bool runOnModule(Module &M) override {
+    MachineModuleInfo &MMI =
+        getAnalysis<MachineModuleInfoWrapperPass>().getMMI();
+
+    bool Changed = false;
+    for (Function &F : M.functions()) {
+      MachineFunction &MF = MMI.getOrCreateMachineFunction(F);
+      for (MachineBasicBlock &MBB : MF) {
+        for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
+             I != E;) {
+          if (I->isDebugInstr()) {
+            // FIXME: We should remove all of them. However, AArch64 emits an
+            //        invalid `DBG_VALUE $lr` with only one operand instead of
+            //        the usual three and has a test that depends on it's
+            //        preservation. Preserve it for now.
+            if (I->getNumOperands() > 1) {
+              LLVM_DEBUG(dbgs() << "Removing debug instruction " << *I);
+              I = MBB.erase(I);
+              Changed |= true;
+              continue;
+            }
+          }
+          if (I->getDebugLoc()) {
+            LLVM_DEBUG(dbgs() << "Removing location " << *I);
+            I->setDebugLoc(DebugLoc());
+            Changed |= true;
+            ++I;
+            continue;
+          }
+          LLVM_DEBUG(dbgs() << "Keeping " << *I);
+          ++I;
+        }
+      }
+    }
+
+    Changed |= StripDebugInfo(M);
+
+    NamedMDNode *NMD = M.getNamedMetadata("llvm.debugify");
+    if (NMD) {
+      NMD->eraseFromParent();
+      Changed |= true;
+    }
+
+    NMD = M.getModuleFlagsMetadata();
+    if (NMD) {
+      // There must be an easier way to remove an operand from a NamedMDNode.
+      SmallVector<MDNode *, 4> Flags;
+      for (MDNode *Flag : NMD->operands())
+        Flags.push_back(Flag);
+      NMD->clearOperands();
+      for (MDNode *Flag : Flags) {
+        MDString *Key = dyn_cast_or_null<MDString>(Flag->getOperand(1));
+        if (Key->getString() == "Debug Info Version") {
+          Changed |= true;
+          continue;
+        }
+        NMD->addOperand(Flag);
+      }
+      // If we left it empty we might as well remove it.
+      if (NMD->getNumOperands() == 0)
+        NMD->eraseFromParent();
+    }
+
+    return Changed;
+  }
+
+  StripDebugMachineModule() : ModulePass(ID) {}
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.addRequired<MachineModuleInfoWrapperPass>();
+    AU.addPreserved<MachineModuleInfoWrapperPass>();
+  }
+
+  static char ID; // Pass identification.
+};
+char StripDebugMachineModule::ID = 0;
+
+} // end anonymous namespace
+
+INITIALIZE_PASS_BEGIN(StripDebugMachineModule, DEBUG_TYPE,
+                      "Machine Strip Debug Module", false, false)
+INITIALIZE_PASS_END(StripDebugMachineModule, DEBUG_TYPE,
+                    "Machine Strip Debug Module", false, false)
+
+ModulePass *createStripDebugMachineModulePass() {
+  return new StripDebugMachineModule();
+}