Map Parameters marked as dereferenceable during inlining to loads.

[mcberg2017]

Summary

If a call has a Dereferenceable parameter and the call site provides
a pointer load to that parameter, walk all load's uses and validate
that all the calls we find have at least one parameter which
shares this property and matches the same definition.

I have done this as an existence walk, but it could just as easily be an intersection
of all the loads parameters that are used in calls.

[jdoerfert]

I doubt this is correct. One problem below, one inlined.

int callee(int *a) { return *a; }
void caller(int **p, int c) {
  int *a = *p;
  if (c)
    callee(a);
}

llvm/lib/Transforms/Utils/InlineFunction.cpp

1678

I don't understand how we can ignore non call uses but somehow need a property of call uses, I'm fairly certain a simple bitcast will break this.

[lebedev.ri]

This review seems to be stuck/dead, consider abandoning if no longer relevant.

llvm/lib/Transforms/Utils/InlineFunction.cpp

llvm::InlineResult llvm::InlineFunction(CallBase &CB, InlineFunctionInfo &IFI,
   // If IFI has any state in it, zap it before we fill it in.
   IFI.reset();
 
   Function *CalledFunc = CB.getCalledFunction();
   if (!CalledFunc ||               // Can't inline external function or indirect
       CalledFunc->isDeclaration()) // call!
     return InlineResult::failure("external or indirect");
 
+  // If the current call has a Dereferenceable parameter at ArgNo,
+  // walk all ActualArg's (which must be a load) uses and validate that all the
+  // calls we find have at least one parameter which shares this property and
+  // match the same definition as ActualArg.
+  auto HaveQualifyingDerefLoads = [CalledFunc](Value *ActualArg, unsigned ArgNo,
+                                               LoadInst *LI) {
+    // Must have a param that is Dereferenceable as a use of this LI.
+    // This is our entry criteria to keep us from iterating on the uses of
+    // each load.
+    if (!CalledFunc->hasParamAttribute(ArgNo, Attribute::Dereferenceable))
+      return false;
+
+    // If the load already has MD_dereferenceable, there nothing to do.
+    if (LI->getMetadata(LLVMContext::MD_dereferenceable))
+      return false;
+
+    // We want to place this attribute on the load iff all uses
+    // that are calls have MD_dereferenceable params.
+    for (User *Use : LI->users()) {
+      // Nothing to analyze.
+      if (!isa<CallInst>(Use))
+        continue;
+
+      CallInst *CI = cast<CallInst>(Use);
+      Function *CurFunc = CI->getCalledFunction();
+      CallBase *CurCS = dyn_cast<CallBase>(CI);
+      auto CurAI = CurCS->arg_begin();
+      bool FoundDereferenceableParam = false;
+      unsigned CurArgNo = 0;
+      for (Function::arg_iterator CurI = CurFunc->arg_begin(),
+                                  CurE = CurFunc->arg_end();
+           CurI != CurE; ++CurI, ++CurAI, ++CurArgNo) {
+        Value *CurArg = *CurAI;
+        if (CurFunc->hasParamAttribute(CurArgNo, Attribute::Dereferenceable)) {
+          if (CurArg == ActualArg) {
+            FoundDereferenceableParam = true;
+            break;
+          }
+        }
+      }
+      if (!FoundDereferenceableParam)
+        return false;
+    }
+
+    return true;
+  };
+
   // The inliner does not know how to inline through calls with operand bundles
   // in general ...
   if (CB.hasOperandBundles()) {
     for (int i = 0, e = CB.getNumOperandBundles(); i != e; ++i) {
       uint32_t Tag = CB.getOperandBundleAt(i).getTagID();
       // ... but it knows how to inline through "deopt" operand bundles ...
       if (Tag == LLVMContext::OB_deopt)
         continue;
for (Function::arg_iterator I = CalledFunc->arg_begin(),
       // by them explicit.  However, we don't do this if the callee is readonly
       // or readnone, because the copy would be unneeded: the callee doesn't
       // modify the struct.
       if (CB.isByValArgument(ArgNo)) {
         ActualArg = HandleByValArgument(ActualArg, &CB, CalledFunc, IFI,
                                         CalledFunc->getParamAlignment(ArgNo));
         if (ActualArg != *AI)
           ByValInit.push_back(std::make_pair(ActualArg, (Value*) *AI));
+      } else if (auto LI = dyn_cast<LoadInst>(ActualArg)) {
+        // Mark loads which have calls with dereferenceable parameters with
+        // their dereferenceable metadata.
+        if (HaveQualifyingDerefLoads(ActualArg, ArgNo, LI)) {
+          uint64_t DerefBytes = CalledFunc->getParamDereferenceableBytes(ArgNo);
+          auto &Ctx = LI->getContext();
+          MDBuilder MDB(Ctx);
+          LI->setMetadata(
+              LLVMContext::MD_dereferenceable,
+              MDNode::get(Ctx, MDB.createConstant(ConstantInt::get(
+                                   Type::getInt64Ty(Ctx), DerefBytes))));
+        }
       }
 
       VMap[&*I] = ActualArg;
     }
 
     // TODO: Remove this when users have been updated to the assume bundles.
     // Add alignment assumptions if necessary. We do this before the inlined
     // instructions are actually cloned into the caller so that we can easily

llvm/test/Transforms/Inline/inline-dereferenceable.ll

+; RUN: opt -S -inline < %s | FileCheck %s
+
+; Map dereferenceable on the load that provides the parameter to inner
+; via the dereferenceable parameter definition in the inliner.
+
+%struct._primitive_acceleration_structure_t = type opaque
+%struct.Header = type { i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i64, %struct._Box }
+%struct._Box = type { [3 x float], [3 x float] }
+
+@buffer_pointers.0 = external constant %struct._primitive_acceleration_structure_t*, section "buffer_bindings", align 8
+
+; CHECK: define i32 @inner(%struct.Header* nocapture readonly dereferenceable(96) %a)
+define i32 @inner(%struct.Header* nocapture readonly dereferenceable(96) %a) {
+  %innerNodeOffset.i = getelementptr inbounds %struct.Header, %struct.Header* %a, i32 0, i32 9
+  %x = load i32, i32* %innerNodeOffset.i, align 4
+  ret i32 %x
+}
+
+define i32 @outer() {
+; CHECK: %struct = load %struct.Header*, %struct.Header** bitcast (%struct._primitive_acceleration_structure_t** @buffer_pointers.0 to %struct.Header**), align 8, !dereferenceable !0
+   %struct = load %struct.Header*, %struct.Header** bitcast (%struct._primitive_acceleration_structure_t** @buffer_pointers.0 to %struct.Header**), align 8
+   %r = call i32 @inner(%struct.Header* %struct)
+   ret i32 %r
+}
+