LowerDbgDeclare: ignore dbg.declares for allocas with volatile access

There is no point in lowering a dbg.declare describing an alloca that
has volatile loads or stores as users, since the alloca cannot be
elided. Lowering the dbg.declare will result in larger debug info that
may also have worse coverage than just describing the alloca.

rdar://problem/34496278

llvm-svn: 327092

1 files changed, 28 insertions, 17 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 1bfa1be..cd96847c 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1322,25 +1322,36 @@ bool llvm::LowerDbgDeclare(Function &F) {
     // stored on the stack, while the dbg.declare can only describe
     // the stack slot (and at a lexical-scope granularity). Later
     // passes will attempt to elide the stack slot.
-    if (AI && !isArray(AI)) {
-      for (auto &AIUse : AI->uses()) {
-        User *U = AIUse.getUser();
-        if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
-          if (AIUse.getOperandNo() == 1)
-            ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
-        } else if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
-          ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
-        } else if (CallInst *CI = dyn_cast<CallInst>(U)) {
-          // This is a call by-value or some other instruction that
-          // takes a pointer to the variable. Insert a *value*
-          // intrinsic that describes the alloca.
-          DIB.insertDbgValueIntrinsic(AI, DDI->getVariable(),
-                                      DDI->getExpression(), DDI->getDebugLoc(),
-                                      CI);
-        }
+    if (!AI || isArray(AI))
+      continue;
+
+    // A volatile load/store means that the alloca can't be elided anyway.
+    if (llvm::any_of(AI->users(), [](User *U) -> bool {
+          if (LoadInst *LI = dyn_cast<LoadInst>(U))
+            return LI->isVolatile();
+          if (StoreInst *SI = dyn_cast<StoreInst>(U))
+            return SI->isVolatile();
+          return false;
+        }))
+      continue;
+
+    for (auto &AIUse : AI->uses()) {
+      User *U = AIUse.getUser();
+      if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
+        if (AIUse.getOperandNo() == 1)
+          ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
+      } else if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
+        ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
+      } else if (CallInst *CI = dyn_cast<CallInst>(U)) {
+        // This is a call by-value or some other instruction that
+        // takes a pointer to the variable. Insert a *value*
+        // intrinsic that describes the alloca.
+        DIB.insertDbgValueIntrinsic(AI, DDI->getVariable(),
+                                    DDI->getExpression(), DDI->getDebugLoc(),
+                                    CI);
       }
-      DDI->eraseFromParent();
     }
+    DDI->eraseFromParent();
   }
   return true;
 }