[llvm] [NFC] clean up memtag-stack code (PR #80906)

[Florian Mayer via llvm-commits]

https://github.com/fmayer created https://github.com/llvm/llvm-project/pull/80906

we would replace the alloca with tagp for debug instructions, then replace it back with the original alloca. it's easier to just skip the replacement.

>From bcdadcfcedeb64dc4224cefcb8fe82ff0e860175 Mon Sep 17 00:00:00 2001
From: Florian Mayer <fmayer at google.com>
Date: Thu, 1 Feb 2024 17:49:21 -0800
Subject: [PATCH] [NFC] clean up memtag-stack code

we would replace the alloca with tagp for debug instructions, then
replace it back with the original alloca. it's easier to just skip the
replacement.
---
 llvm/lib/Target/AArch64/AArch64StackTagging.cpp | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/llvm/lib/Target/AArch64/AArch64StackTagging.cpp b/llvm/lib/Target/AArch64/AArch64StackTagging.cpp
index 961dded1323436..15d81c2f44a5b0 100644
--- a/llvm/lib/Target/AArch64/AArch64StackTagging.cpp
+++ b/llvm/lib/Target/AArch64/AArch64StackTagging.cpp
@@ -21,7 +21,6 @@
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
 #include "llvm/Analysis/StackSafetyAnalysis.h"
-#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/CodeGen/LiveRegUnits.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineFunction.h"
@@ -520,7 +519,6 @@ bool AArch64StackTagging::runOnFunction(Function &Fn) {
   for (auto &I : SInfo.AllocasToInstrument) {
     memtag::AllocaInfo &Info = I.second;
     assert(Info.AI && SIB.isInterestingAlloca(*Info.AI));
-    TrackingVH<Instruction> OldAI = Info.AI;
     memtag::alignAndPadAlloca(Info, kTagGranuleSize);
     AllocaInst *AI = Info.AI;
     int Tag = NextTag;
@@ -534,7 +532,9 @@ bool AArch64StackTagging::runOnFunction(Function &Fn) {
                               ConstantInt::get(IRB.getInt64Ty(), Tag)});
     if (Info.AI->hasName())
       TagPCall->setName(Info.AI->getName() + ".tag");
-    Info.AI->replaceAllUsesWith(TagPCall);
+    // Does not replace metadata, so we don't have to handle DPValues.
+    Info.AI->replaceUsesWithIf(
+        TagPCall, [&](Use &U) { return !isa<DbgVariableIntrinsic>(U); });
     TagPCall->setOperand(0, Info.AI);
 
     // Calls to functions that may return twice (e.g. setjmp) confuse the
@@ -574,12 +574,6 @@ bool AArch64StackTagging::runOnFunction(Function &Fn) {
       for (auto *II : Info.LifetimeEnd)
         II->eraseFromParent();
     }
-
-    // Fixup debug intrinsics to point to the new alloca.
-    for (auto *DVI : Info.DbgVariableIntrinsics)
-      DVI->replaceVariableLocationOp(OldAI, Info.AI);
-    for (auto *DPV : Info.DbgVariableRecords)
-      DPV->replaceVariableLocationOp(OldAI, Info.AI);
   }
 
   // If we have instrumented at least one alloca, all unrecognized lifetime