Implement strip.invariant.group

Summary:
This patch introduce new intrinsic -
strip.invariant.group that was described in the
RFC: Devirtualization v2

Reviewers: rsmith, hfinkel, nlopes, sanjoy, amharc, kuhar

Subscribers: arsenm, nhaehnle, JDevlieghere, hiraditya, xbolva00, llvm-commits

Differential Revision: https://reviews.llvm.org/D47103

Co-authored-by: Krzysztof Pszeniczny <krzysztof.pszeniczny@gmail.com>
llvm-svn: 336073

llvm/docs/LangRef.rst

@@ -13350,16 +13350,17 @@ Overview:
 """""""""
 
 The '``llvm.launder.invariant.group``' intrinsic can be used when an invariant
-established by invariant.group metadata no longer holds, to obtain a new pointer
-value that does not carry the invariant information. It is an experimental
-intrinsic, which means that its semantics might change in the future.
+established by ``invariant.group`` metadata no longer holds, to obtain a new
+pointer value that carries fresh invariant group information. It is an
+experimental intrinsic, which means that its semantics might change in the
+future.
 
 
 Arguments:
 """"""""""
 
-The ``llvm.launder.invariant.group`` takes only one argument, which is
-the pointer to the memory for which the ``invariant.group`` no longer holds.
+The ``llvm.launder.invariant.group`` takes only one argument, which is a pointer
+to the memory.
 
 Semantics:
 """"""""""
@@ -13368,6 +13369,43 @@ Returns another pointer that aliases its argument but which is considered differ
 for the purposes of ``load``/``store`` ``invariant.group`` metadata.
 It does not read any accessible memory and the execution can be speculated.
 
+'``llvm.strip.invariant.group``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic. The memory object can belong to any address
+space. The returned pointer must belong to the same address space as the
+argument.
+
+::
+
+      declare i8* @llvm.strip.invariant.group.p0i8(i8* <ptr>)
+
+Overview:
+"""""""""
+
+The '``llvm.strip.invariant.group``' intrinsic can be used when an invariant
+established by ``invariant.group`` metadata no longer holds, to obtain a new pointer
+value that does not carry the invariant information. It is an experimental
+intrinsic, which means that its semantics might change in the future.
+
+
+Arguments:
+""""""""""
+
+The ``llvm.strip.invariant.group`` takes only one argument, which is a pointer
+to the memory.
+
+Semantics:
+""""""""""
+
+Returns another pointer that aliases its argument but which has no associated
+``invariant.group`` metadata.
+It does not read any memory and can be speculated.
+
+
+
 .. _constrainedfp:
 
 Constrained Floating-Point Intrinsics

llvm/include/llvm/IR/IRBuilder.h

@@ -2022,6 +2022,7 @@ class IRBuilder : public IRBuilderBase, public Inserter {
   Value *CreateLaunderInvariantGroup(Value *Ptr) {
     assert(isa<PointerType>(Ptr->getType()) &&
            "launder.invariant.group only applies to pointers.");
+    // FIXME: we could potentially avoid casts to/from i8*.
     auto *PtrType = Ptr->getType();
     auto *Int8PtrTy = getInt8PtrTy(PtrType->getPointerAddressSpace());
     if (PtrType != Int8PtrTy)
@@ -2042,6 +2043,34 @@ class IRBuilder : public IRBuilderBase, public Inserter {
     return Fn;
   }
 
+  /// \brief Create a strip.invariant.group intrinsic call. If Ptr type is
+  /// different from pointer to i8, it's casted to pointer to i8 in the same
+  /// address space before call and casted back to Ptr type after call.
+  Value *CreateStripInvariantGroup(Value *Ptr) {
+    assert(isa<PointerType>(Ptr->getType()) &&
+           "strip.invariant.group only applies to pointers.");
+
+    // FIXME: we could potentially avoid casts to/from i8*.
+    auto *PtrType = Ptr->getType();
+    auto *Int8PtrTy = getInt8PtrTy(PtrType->getPointerAddressSpace());
+    if (PtrType != Int8PtrTy)
+      Ptr = CreateBitCast(Ptr, Int8PtrTy);
+    Module *M = BB->getParent()->getParent();
+    Function *FnStripInvariantGroup = Intrinsic::getDeclaration(
+        M, Intrinsic::strip_invariant_group, {Int8PtrTy});
+
+    assert(FnStripInvariantGroup->getReturnType() == Int8PtrTy &&
+           FnStripInvariantGroup->getFunctionType()->getParamType(0) ==
+               Int8PtrTy &&
+           "StripInvariantGroup should take and return the same type");
+
+    CallInst *Fn = CreateCall(FnStripInvariantGroup, {Ptr});
+
+    if (PtrType != Int8PtrTy)
+      return CreateBitCast(Fn, PtrType);
+    return Fn;
+  }
+
   /// Return a vector value that contains \arg V broadcasted to \p
   /// NumElts elements.
   Value *CreateVectorSplat(unsigned NumElts, Value *V, const Twine &Name = "") {

llvm/include/llvm/IR/Intrinsics.td

@@ -728,6 +728,11 @@ def int_launder_invariant_group : Intrinsic<[llvm_anyptr_ty],
                                             [LLVMMatchType<0>],
                                             [IntrInaccessibleMemOnly, IntrSpeculatable]>;
 
+
+def int_strip_invariant_group : Intrinsic<[llvm_anyptr_ty],
+                                          [LLVMMatchType<0>],
+                                          [IntrSpeculatable, IntrNoMem]>;
+
 //===------------------------ Stackmap Intrinsics -------------------------===//
 //
 def int_experimental_stackmap : Intrinsic<[],

llvm/lib/Analysis/BasicAliasAnalysis.cpp

@@ -431,13 +431,15 @@ bool BasicAAResult::DecomposeGEPExpression(const Value *V,
     const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
     if (!GEPOp) {
       if (auto CS = ImmutableCallSite(V)) {
-        // Note: getArgumentAliasingToReturnedPointer keeps it in sync with
-        // CaptureTracking, which is needed for correctness.  This is because
-        // some intrinsics like launder.invariant.group returns pointers that
-        // are aliasing it's argument, which is known to CaptureTracking.
-        // If AliasAnalysis does not use the same information, it could assume
-        // that pointer returned from launder does not alias it's argument
-        // because launder could not return it if the pointer was not captured.
+        // CaptureTracking can know about special capturing properties of some
+        // intrinsics like launder.invariant.group, that can't be expressed with
+        // the attributes, but have properties like returning aliasing pointer.
+        // Because some analysis may assume that nocaptured pointer is not
+        // returned from some special intrinsic (because function would have to
+        // be marked with returns attribute), it is crucial to use this function
+        // because it should be in sync with CaptureTracking. Not using it may
+        // cause weird miscompilations where 2 aliasing pointers are assumed to
+        // noalias.
         if (auto *RP = getArgumentAliasingToReturnedPointer(CS)) {
           V = RP;
           continue;

llvm/lib/Analysis/ConstantFolding.cpp

@@ -1393,6 +1393,7 @@ bool llvm::canConstantFoldCallTo(ImmutableCallSite CS, const Function *F) {
   case Intrinsic::fmuladd:
   case Intrinsic::copysign:
   case Intrinsic::launder_invariant_group:
+  case Intrinsic::strip_invariant_group:
   case Intrinsic::round:
   case Intrinsic::masked_load:
   case Intrinsic::sadd_with_overflow:
@@ -1596,14 +1597,16 @@ Constant *ConstantFoldScalarCall(StringRef Name, unsigned IntrinsicID, Type *Ty,
         return Constant::getNullValue(Ty);
       if (IntrinsicID == Intrinsic::bswap ||
           IntrinsicID == Intrinsic::bitreverse ||
-          IntrinsicID == Intrinsic::launder_invariant_group)
+          IntrinsicID == Intrinsic::launder_invariant_group ||
+          IntrinsicID == Intrinsic::strip_invariant_group)
         return Operands[0];
     }
 
     if (isa<ConstantPointerNull>(Operands[0]) &&
         Operands[0]->getType()->getPointerAddressSpace() == 0) {
-      // launder(null) == null iff in addrspace 0
-      if (IntrinsicID == Intrinsic::launder_invariant_group)
+      // launder(null) == null == strip(null) iff in addrspace 0
+      if (IntrinsicID == Intrinsic::launder_invariant_group ||
+          IntrinsicID == Intrinsic::strip_invariant_group)
         return Operands[0];
       return nullptr;
     }

llvm/lib/Analysis/ValueTracking.cpp

@@ -3404,8 +3404,9 @@ const Value *llvm::getArgumentAliasingToReturnedPointer(ImmutableCallSite CS) {
 }
 
 bool llvm::isIntrinsicReturningPointerAliasingArgumentWithoutCapturing(
-      ImmutableCallSite CS) {
-  return CS.getIntrinsicID() == Intrinsic::launder_invariant_group;
+    ImmutableCallSite CS) {
+  return CS.getIntrinsicID() == Intrinsic::launder_invariant_group ||
+         CS.getIntrinsicID() == Intrinsic::strip_invariant_group;
 }
 
 /// \p PN defines a loop-variant pointer to an object.  Check if the
@@ -3454,13 +3455,15 @@ Value *llvm::GetUnderlyingObject(Value *V, const DataLayout &DL,
       return V;
     } else {
       if (auto CS = CallSite(V)) {
-        // Note: getArgumentAliasingToReturnedPointer keeps it in sync with
-        // CaptureTracking, which is needed for correctness.  This is because
-        // some intrinsics like launder.invariant.group returns pointers that
-        // are aliasing it's argument, which is known to CaptureTracking.
-        // If AliasAnalysis does not use the same information, it could assume
-        // that pointer returned from launder does not alias it's argument
-        // because launder could not return it if the pointer was not captured.
+        // CaptureTracking can know about special capturing properties of some
+        // intrinsics like launder.invariant.group, that can't be expressed with
+        // the attributes, but have properties like returning aliasing pointer.
+        // Because some analysis may assume that nocaptured pointer is not
+        // returned from some special intrinsic (because function would have to
+        // be marked with returns attribute), it is crucial to use this function
+        // because it should be in sync with CaptureTracking. Not using it may
+        // cause weird miscompilations where 2 aliasing pointers are assumed to
+        // noalias.
         if (auto *RP = getArgumentAliasingToReturnedPointer(CS)) {
           V = RP;
           continue;

llvm/lib/CodeGen/CodeGenPrepare.cpp

@@ -1702,6 +1702,7 @@ bool CodeGenPrepare::optimizeCallInst(CallInst *CI, bool &ModifiedDT) {
       return true;
     }
     case Intrinsic::launder_invariant_group:
+    case Intrinsic::strip_invariant_group:
       II->replaceAllUsesWith(II->getArgOperand(0));
       II->eraseFromParent();
       return true;

llvm/lib/CodeGen/SelectionDAG/FastISel.cpp

@@ -1437,6 +1437,7 @@ bool FastISel::selectIntrinsicCall(const IntrinsicInst *II) {
     return true;
   }
   case Intrinsic::launder_invariant_group:
+  case Intrinsic::strip_invariant_group:
   case Intrinsic::expect: {
     unsigned ResultReg = getRegForValue(II->getArgOperand(0));
     if (!ResultReg)

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -5768,6 +5768,7 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
   case Intrinsic::annotation:
   case Intrinsic::ptr_annotation:
   case Intrinsic::launder_invariant_group:
+  case Intrinsic::strip_invariant_group:
     // Drop the intrinsic, but forward the value
     setValue(&I, getValue(I.getOperand(0)));
     return nullptr;

llvm/lib/IR/Value.cpp

@@ -521,7 +521,8 @@ static const Value *stripPointerCastsAndOffsets(const Value *V) {
         // but it can't be marked with returned attribute, that's why it needs
         // special case.
         if (StripKind == PSK_ZeroIndicesAndAliasesAndInvariantGroups &&
-            CS.getIntrinsicID() == Intrinsic::launder_invariant_group) {
+            (CS.getIntrinsicID() == Intrinsic::launder_invariant_group ||
+             CS.getIntrinsicID() == Intrinsic::strip_invariant_group)) {
           V = CS.getArgOperand(0);
           continue;
         }

llvm/lib/Target/AMDGPU/AMDGPUPromoteAlloca.cpp

@@ -457,6 +457,7 @@ static bool isCallPromotable(CallInst *CI) {
   case Intrinsic::invariant_start:
   case Intrinsic::invariant_end:
   case Intrinsic::launder_invariant_group:
+  case Intrinsic::strip_invariant_group:
   case Intrinsic::objectsize:
     return true;
   default:
@@ -882,6 +883,7 @@ bool AMDGPUPromoteAlloca::handleAlloca(AllocaInst &I, bool SufficientLDS) {
     case Intrinsic::invariant_start:
     case Intrinsic::invariant_end:
     case Intrinsic::launder_invariant_group:
+    case Intrinsic::strip_invariant_group:
       Intr->eraseFromParent();
       // FIXME: I think the invariant marker should still theoretically apply,
       // but the intrinsics need to be changed to accept pointers with any

llvm/test/Analysis/ValueTracking/invariant.group.ll

@@ -1,7 +1,7 @@
 ; RUN: opt -S -instsimplify -instcombine < %s | FileCheck %s
 
-; CHECK-LABEL: define void @checkNonnull()
-define void @checkNonnull() {
+; CHECK-LABEL: define void @checkNonnullLaunder()
+define void @checkNonnullLaunder() {
 ; CHECK:   %p = call i8* @llvm.launder.invariant.group.p0i8(i8* nonnull %0)
 ; CHECK:   %p2 = call i8* @llvm.launder.invariant.group.p0i8(i8* nonnull %p)
 ; CHECK:   call void @use(i8* nonnull %p2)
@@ -15,5 +15,22 @@ entry:
   ret void
 }
 
+; CHECK-LABEL: define void @checkNonnullStrip()
+define void @checkNonnullStrip() {
+; CHECK:   %p = call i8* @llvm.strip.invariant.group.p0i8(i8* nonnull %0)
+; CHECK:   %p2 = call i8* @llvm.strip.invariant.group.p0i8(i8* nonnull %p)
+; CHECK:   call void @use(i8* nonnull %p2)
+entry:
+  %0 = alloca i8, align 8
+
+  %p = call i8* @llvm.strip.invariant.group.p0i8(i8* %0)
+  %p2 = call i8* @llvm.strip.invariant.group.p0i8(i8* %p)
+  call void @use(i8* %p2)
+
+  ret void
+}
+
 declare i8* @llvm.launder.invariant.group.p0i8(i8*)
+declare i8* @llvm.strip.invariant.group.p0i8(i8*)
+
 declare void @use(i8*)

llvm/test/CodeGen/Generic/intrinsics.ll

@@ -41,11 +41,19 @@ define double @test_cos(float %F) {
 
 declare i8* @llvm.launder.invariant.group(i8*)
 
-define i8* @barrier(i8* %p) {
+define i8* @launder(i8* %p) {
         %q = call i8* @llvm.launder.invariant.group(i8* %p)
         ret i8* %q
 }
 
+declare i8* @llvm.strip.invariant.group(i8*)
+
+define i8* @strip(i8* %p) {
+        %q = call i8* @llvm.strip.invariant.group(i8* %p)
+        ret i8* %q
+}
+
+
 ; sideeffect
 
 declare void @llvm.sideeffect()

llvm/test/Other/launder.invariant.group.ll → llvm/test/Other/invariant.group.ll

@@ -77,8 +77,14 @@ define i8 @unoptimizable2() {
 define void @dontProveEquality(i8* %a) {
   %b = call i8* @llvm.launder.invariant.group.p0i8(i8* %a)
   %r = icmp eq i8* %b, %a
-;CHECK: call void @useBool(i1 %r)
+; CHECK: call void @useBool(i1 %r)
   call void @useBool(i1 %r)
+
+  %b2 = call i8* @llvm.strip.invariant.group.p0i8(i8* %a)
+  %r2 = icmp eq i8* %b2, %a
+; CHECK: call void @useBool(i1 %r2)
+  call void @useBool(i1 %r2)
+
   ret void
 }
 
@@ -90,5 +96,9 @@ declare void @clobber(i8*)
 ; CHECK-NEXT: declare i8* @llvm.launder.invariant.group.p0i8(i8*)
 declare i8* @llvm.launder.invariant.group.p0i8(i8*)
 
-!0 = !{}
+; CHECK: Function Attrs: nounwind readnone speculatable{{$}}
+; CHECK-NEXT: declare i8* @llvm.strip.invariant.group.p0i8(i8*)
+declare i8* @llvm.strip.invariant.group.p0i8(i8*)
+
 
+!0 = !{}

llvm/test/Transforms/CodeGenPrepare/invariant.group.ll

@@ -7,8 +7,8 @@ define void @foo() {
 enter:
   ; CHECK-NOT: !invariant.group
   ; CHECK-NOT: @llvm.launder.invariant.group.p0i8(
-  ; CHECK: %val = load i8, i8* @tmp, !tbaa
-  %val = load i8, i8* @tmp, !invariant.group !0, !tbaa !{!1, !1, i64 0}
+  ; CHECK: %val = load i8, i8* @tmp{{$}}
+  %val = load i8, i8* @tmp, !invariant.group !0
   %ptr = call i8* @llvm.launder.invariant.group.p0i8(i8* @tmp)
 
   ; CHECK: store i8 42, i8* @tmp{{$}}
@@ -18,7 +18,23 @@ enter:
 }
 ; CHECK-LABEL: }
 
-declare i8* @llvm.launder.invariant.group.p0i8(i8*)
+; CHECK-LABEL: define void @foo2() {
+define void @foo2() {
+enter:
+  ; CHECK-NOT: !invariant.group
+  ; CHECK-NOT: @llvm.strip.invariant.group.p0i8(
+  ; CHECK: %val = load i8, i8* @tmp{{$}}
+  %val = load i8, i8* @tmp, !invariant.group !0
+  %ptr = call i8* @llvm.strip.invariant.group.p0i8(i8* @tmp)
+
+  ; CHECK: store i8 42, i8* @tmp{{$}}
+  store i8 42, i8* %ptr, !invariant.group !0
 
+  ret void
+}
+; CHECK-LABEL: }
+
+
+declare i8* @llvm.launder.invariant.group.p0i8(i8*)
+declare i8* @llvm.strip.invariant.group.p0i8(i8*)
 !0 = !{}
-!1 = !{!"x", !0}