[llvm] d64a0a9 - [ValueTracking] Make `getUnderlyingObjectsForCodegen()` preserve unidentified objects (#224584)

[via llvm-commits]

Author: Nathan Corbyn
Date: 2026-09-21T12:49:57+01:00
New Revision: d64a0a9effc7704962e21ede22eb0f5ba24e4390

URL: https://github.com/llvm/llvm-project/commit/d64a0a9effc7704962e21ede22eb0f5ba24e4390
DIFF: https://github.com/llvm/llvm-project/commit/d64a0a9effc7704962e21ede22eb0f5ba24e4390.diff

LOG: [ValueTracking] Make `getUnderlyingObjectsForCodegen()` preserve unidentified objects (#224584)

In some situations, it is useful to inspect the underlying objects of a
memory operation, even if they may alias with one another. A concrete
example comes from the approach to schedule DAG construction I've been
developing (see #205689) where these objects are used to infer that a
class of control dependencies between memory operations is redundant,
whereby eliminating the compile time cost of recording them. Update
`getUnderlyingObjectsForCodegen()` to return these objects.

Split from https://github.com/llvm/llvm-project/pull/205689

Added: 
    

Modified: 
    llvm/include/llvm/Analysis/ValueTracking.h
    llvm/lib/Analysis/ValueTracking.cpp
    llvm/lib/CodeGen/StackColoring.cpp
    llvm/lib/Transforms/Utils/MemoryOpRemark.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/Analysis/ValueTracking.h b/llvm/include/llvm/Analysis/ValueTracking.h
index 43dd1bbafbc49..965b69cae0db0 100644
--- a/llvm/include/llvm/Analysis/ValueTracking.h
+++ b/llvm/include/llvm/Analysis/ValueTracking.h
@@ -531,6 +531,10 @@ LLVM_ABI void getUnderlyingObjects(const Value *V,
 
 /// This is a wrapper around getUnderlyingObjects and adds support for basic
 /// ptrtoint+arithmetic+inttoptr sequences.
+///
+/// Return true if each of the underlying objects is identified. \p Objects is
+/// never cleared, so may contain unidentified objects when the return value is
+/// false.
 LLVM_ABI bool getUnderlyingObjectsForCodeGen(const Value *V,
                                              SmallVectorImpl<Value *> &Objects);
 

diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index fbd57012d1a4f..1286130cf5d94 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -7467,6 +7467,7 @@ bool llvm::getUnderlyingObjectsForCodeGen(const Value *V,
                                           SmallVectorImpl<Value *> &Objects) {
   SmallPtrSet<const Value *, 16> Visited;
   SmallVector<const Value *, 4> Working(1, V);
+  bool AllObjectsIdentified = true;
   do {
     V = Working.pop_back_val();
 
@@ -7484,16 +7485,11 @@ bool llvm::getUnderlyingObjectsForCodeGen(const Value *V,
           continue;
         }
       }
-      // If getUnderlyingObjects fails to find an identifiable object,
-      // getUnderlyingObjectsForCodeGen also fails for safety.
-      if (!isIdentifiedObject(V)) {
-        Objects.clear();
-        return false;
-      }
+      AllObjectsIdentified &= isIdentifiedObject(V);
       Objects.push_back(const_cast<Value *>(V));
     }
   } while (!Working.empty());
-  return true;
+  return AllObjectsIdentified;
 }
 
 AllocaInst *llvm::findAllocaForValue(Value *V, bool OffsetZero) {

diff  --git a/llvm/lib/CodeGen/StackColoring.cpp b/llvm/lib/CodeGen/StackColoring.cpp
index 0e4c1526d0d0b..81e4e1bfdefbf 100644
--- a/llvm/lib/CodeGen/StackColoring.cpp
+++ b/llvm/lib/CodeGen/StackColoring.cpp
@@ -1070,9 +1070,8 @@ void StackColoring::remapInstructions(DenseMap<int, int> &SlotRemap) {
         if (MMO->getAAInfo()) {
           if (const Value *MMOV = MMO->getValue()) {
             SmallVector<Value *, 4> Objs;
-            getUnderlyingObjectsForCodeGen(MMOV, Objs);
 
-            if (Objs.empty())
+            if (!getUnderlyingObjectsForCodeGen(MMOV, Objs) || Objs.empty())
               MayHaveConflictingAAMD = true;
             else
               for (Value *V : Objs) {

diff  --git a/llvm/lib/Transforms/Utils/MemoryOpRemark.cpp b/llvm/lib/Transforms/Utils/MemoryOpRemark.cpp
index 9664773e2d0f4..13933460dce1e 100644
--- a/llvm/lib/Transforms/Utils/MemoryOpRemark.cpp
+++ b/llvm/lib/Transforms/Utils/MemoryOpRemark.cpp
@@ -354,8 +354,11 @@ void MemoryOpRemark::visitVariable(const Value *V,
 void MemoryOpRemark::visitPtr(Value *Ptr, bool IsRead, DiagnosticInfoIROptimization &R) {
   // Find if Ptr is a known variable we can give more information on.
   SmallVector<Value *, 2> Objects;
-  getUnderlyingObjectsForCodeGen(Ptr, Objects);
   SmallVector<VariableInfo, 2> VIs;
+
+  if (!getUnderlyingObjectsForCodeGen(Ptr, Objects))
+    Objects.clear();
+
   for (const Value *V : Objects)
     visitVariable(V, VIs);