[llvm] [Loads] Support dereferenceable assumption with variable size. (PR #128436)

[Nikita Popov via llvm-commits]

================
@@ -174,33 +203,41 @@ static bool isDereferenceableAndAlignedPointer(
   // information for values that cannot be freed in the function.
   // TODO: More precisely check if the pointer can be freed between assumption
   // and use.
-  if (CtxI && !V->canBeFreed()) {
-    /// Look through assumes to see if both dereferencability and alignment can
-    /// be proven by an assume if needed.
-    RetainedKnowledge AlignRK;
-    RetainedKnowledge DerefRK;
-    bool IsAligned = V->getPointerAlignment(DL) >= Alignment;
-    if (getKnowledgeForValue(
-            V, {Attribute::Dereferenceable, Attribute::Alignment}, AC,
-            [&](RetainedKnowledge RK, Instruction *Assume, auto) {
-              if (!isValidAssumeForContext(Assume, CtxI, DT))
-                return false;
-              if (RK.AttrKind == Attribute::Alignment)
-                AlignRK = std::max(AlignRK, RK);
-              if (RK.AttrKind == Attribute::Dereferenceable)
-                DerefRK = std::max(DerefRK, RK);
-              IsAligned |= AlignRK && AlignRK.ArgValue >= Alignment.value();
-              if (IsAligned && DerefRK &&
-                  DerefRK.ArgValue >= Size.getZExtValue())
-                return true; // We have found what we needed so we stop looking
-              return false;  // Other assumes may have better information. so
-                             // keep looking
-            }))
-      return true;
+  if (CtxI) {
+    const Value *UO = getUnderlyingObjectAggressive(V);
+    if (!V->canBeFreed() || (UO && !UO->canBeFreed())) {
+      /// Look through assumes to see if both dereferencability and alignment
+      /// can be proven by an assume if needed.
+      RetainedKnowledge AlignRK;
+      RetainedKnowledge DerefRK;
+      bool IsAligned = V->getPointerAlignment(DL) >= Alignment;
+      if (getKnowledgeForValue(
+              V, {Attribute::Dereferenceable, Attribute::Alignment}, AC,
+              [&](RetainedKnowledge RK, Instruction *Assume, auto) {
+                if (!isValidAssumeForContext(Assume, CtxI, DT))
+                  return false;
+                if (RK.AttrKind == Attribute::Alignment)
+                  AlignRK = std::max(AlignRK, RK);
+                if (RK.AttrKind == Attribute::Dereferenceable)
+                  DerefRK = std::max(DerefRK, RK);
+                IsAligned |= AlignRK && AlignRK.ArgValue >= Alignment.value();
+                if (IsAligned && DerefRK &&
+                    DerefRK.ArgValue >= Size.getZExtValue())
+                  return true; // We have found what we needed so we stop
+                               // looking
+                return false;  // Other assumes may have better information. so
+                               // keep looking
+              }))
+        return true;
+    }
----------------
nikic wrote:

Should this block of code have been removed?

https://github.com/llvm/llvm-project/pull/128436