[llvm] [RemoveDIs][DebugInfo] Correctly visit DPValues in StackInfoBuilder::visit (PR #81247)

[Stephen Tozer via llvm-commits]

https://github.com/SLTozer created https://github.com/llvm/llvm-project/pull/81247

In `StackInfoBuilder::visit(Instruction &Inst)`, operations are performed on memory-related instructions, including debug intrinsics that refer to "interesting" allocas. There is a block that also visits DPValues attached to the instruction, but this block is near the end of the function; this has two problems:
1. The DPValues attached to an instruction precede that instruction, so they should always be processed before the instruction itself.
2. More importantly, some of the paths for visiting other instructions contain early returns, which will result in the DPValues not being visited at all.
This patch simply moves the DPValue-visiting block to the top of the function, which should resolve both of these problems.

>From 6970a1b4fe5b6c3eb186f6f6c86b3df336db52d6 Mon Sep 17 00:00:00 2001
From: Stephen Tozer <Stephen.Tozer at Sony.com>
Date: Fri, 9 Feb 2024 09:53:58 +0000
Subject: [PATCH] Correctly visit DPValues in StackInfoBuilder::visit

---
 .../Transforms/Utils/MemoryTaggingSupport.cpp | 28 +++++++++----------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/llvm/lib/Transforms/Utils/MemoryTaggingSupport.cpp b/llvm/lib/Transforms/Utils/MemoryTaggingSupport.cpp
index 648a5276a3d60..43366950d8df1 100644
--- a/llvm/lib/Transforms/Utils/MemoryTaggingSupport.cpp
+++ b/llvm/lib/Transforms/Utils/MemoryTaggingSupport.cpp
@@ -110,6 +110,20 @@ Instruction *getUntagLocationIfFunctionExit(Instruction &Inst) {
 }
 
 void StackInfoBuilder::visit(Instruction &Inst) {
+  // Check for non-intrinsic debug-info records.
+  for (auto &DPV : Inst.getDbgValueRange()) {
+    for (Value *V : DPV.location_ops()) {
+      if (auto *AI = dyn_cast_or_null<AllocaInst>(V)) {
+        if (!isInterestingAlloca(*AI))
+          continue;
+        AllocaInfo &AInfo = Info.AllocasToInstrument[AI];
+        auto &DPVVec = AInfo.DbgVariableRecords;
+        if (DPVVec.empty() || DPVVec.back() != &DPV)
+          DPVVec.push_back(&DPV);
+      }
+    }
+  }
+
   if (CallInst *CI = dyn_cast<CallInst>(&Inst)) {
     if (CI->canReturnTwice()) {
       Info.CallsReturnTwice = true;
@@ -150,20 +164,6 @@ void StackInfoBuilder::visit(Instruction &Inst) {
     }
   }
 
-  // Check for non-intrinsic debug-info records.
-  for (auto &DPV : Inst.getDbgValueRange()) {
-    for (Value *V : DPV.location_ops()) {
-      if (auto *AI = dyn_cast_or_null<AllocaInst>(V)) {
-        if (!isInterestingAlloca(*AI))
-          continue;
-        AllocaInfo &AInfo = Info.AllocasToInstrument[AI];
-        auto &DPVVec = AInfo.DbgVariableRecords;
-        if (DPVVec.empty() || DPVVec.back() != &DPV)
-          DPVVec.push_back(&DPV);
-      }
-    }
-  }
-
   Instruction *ExitUntag = getUntagLocationIfFunctionExit(Inst);
   if (ExitUntag)
     Info.RetVec.push_back(ExitUntag);