[clang] [llvm] [clang][HLSL][SPRI-V] Add convergence intrinsics (PR #80680)

Nathan Gauër via cfe-commits cfe-commits at lists.llvm.org
Thu Feb 22 12:31:17 PST 2024


https://github.com/Keenuts updated https://github.com/llvm/llvm-project/pull/80680

>From f43134787dc5b1120e3722e03028d0071de22331 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nathan=20Gau=C3=ABr?= <brioche at google.com>
Date: Fri, 2 Feb 2024 16:38:46 +0100
Subject: [PATCH 1/2] [clang][HLSL][SPRI-V] Add convergence intrinsics
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

HLSL has wave operations and other kind of function which required the
control flow to either be converged, or respect certain constraints as
where and how to re-converge.

At the HLSL level, the convergence are mostly obvious: the control flow
is expected to re-converge at the end of a scope.
Once translated to IR, HLSL scopes disapear. This means we need a way to
communicate convergence restrictions down to the backend.

For this, the SPIR-V backend uses convergence intrinsics. So this commit
adds some code to generate convergence intrinsics when required.

This commit is not to be submitted as-is (lacks testing), but
should serve as a basis for an upcoming RFC.

Signed-off-by: Nathan Gauër <brioche at google.com>
---
 clang/lib/CodeGen/CGBuiltin.cpp      | 102 +++++++++++++++++++++++++++
 clang/lib/CodeGen/CGCall.cpp         |   4 ++
 clang/lib/CodeGen/CGLoopInfo.h       |   8 ++-
 clang/lib/CodeGen/CodeGenFunction.h  |  19 +++++
 llvm/include/llvm/IR/IntrinsicInst.h |  13 ++++
 5 files changed, 145 insertions(+), 1 deletion(-)

diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index d8b2115f1e5e3c..82e652959238b4 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -1129,8 +1129,97 @@ struct BitTest {
 
   static BitTest decodeBitTestBuiltin(unsigned BuiltinID);
 };
+
+// Returns the first convergence entry/loop/anchor instruction found in |BB|.
+// std::nullopt otherwise.
+std::optional<llvm::IntrinsicInst *> getConvergenceToken(llvm::BasicBlock *BB) {
+  for (auto &I : *BB) {
+    auto *II = dyn_cast<llvm::IntrinsicInst>(&I);
+    if (II && isConvergenceControlIntrinsic(II->getIntrinsicID()))
+      return II;
+  }
+  return std::nullopt;
+}
+
 } // namespace
 
+llvm::CallBase *
+CodeGenFunction::AddConvergenceControlAttr(llvm::CallBase *Input,
+                                           llvm::Value *ParentToken) {
+  llvm::Value *bundleArgs[] = {ParentToken};
+  llvm::OperandBundleDef OB("convergencectrl", bundleArgs);
+  auto Output = llvm::CallBase::addOperandBundle(
+      Input, llvm::LLVMContext::OB_convergencectrl, OB, Input);
+  Input->replaceAllUsesWith(Output);
+  Input->eraseFromParent();
+  return Output;
+}
+
+llvm::IntrinsicInst *
+CodeGenFunction::EmitConvergenceLoop(llvm::BasicBlock *BB,
+                                     llvm::Value *ParentToken) {
+  CGBuilderTy::InsertPoint IP = Builder.saveIP();
+  Builder.SetInsertPoint(&BB->front());
+  auto CB = Builder.CreateIntrinsic(
+      llvm::Intrinsic::experimental_convergence_loop, {}, {});
+  Builder.restoreIP(IP);
+
+  auto I = AddConvergenceControlAttr(CB, ParentToken);
+  // Controlled convergence is incompatible with uncontrolled convergence.
+  // Removing any old attributes.
+  I->setNotConvergent();
+
+  assert(isa<llvm::IntrinsicInst>(I));
+  return dyn_cast<llvm::IntrinsicInst>(I);
+}
+
+llvm::IntrinsicInst *
+CodeGenFunction::getOrEmitConvergenceEntryToken(llvm::Function *F) {
+  auto *BB = &F->getEntryBlock();
+  auto token = getConvergenceToken(BB);
+  if (token.has_value())
+    return token.value();
+
+  // Adding a convergence token requires the function to be marked as
+  // convergent.
+  F->setConvergent();
+
+  CGBuilderTy::InsertPoint IP = Builder.saveIP();
+  Builder.SetInsertPoint(&BB->front());
+  auto I = Builder.CreateIntrinsic(
+      llvm::Intrinsic::experimental_convergence_entry, {}, {});
+  assert(isa<llvm::IntrinsicInst>(I));
+  Builder.restoreIP(IP);
+
+  return dyn_cast<llvm::IntrinsicInst>(I);
+}
+
+llvm::IntrinsicInst *
+CodeGenFunction::getOrEmitConvergenceLoopToken(const LoopInfo *LI) {
+  assert(LI != nullptr);
+
+  auto token = getConvergenceToken(LI->getHeader());
+  if (token.has_value())
+    return *token;
+
+  llvm::IntrinsicInst *PII =
+      LI->getParent()
+          ? EmitConvergenceLoop(LI->getHeader(),
+                                getOrEmitConvergenceLoopToken(LI->getParent()))
+          : getOrEmitConvergenceEntryToken(LI->getHeader()->getParent());
+
+  return EmitConvergenceLoop(LI->getHeader(), PII);
+}
+
+llvm::CallBase *
+CodeGenFunction::AddControlledConvergenceAttr(llvm::CallBase *Input) {
+  llvm::Value *ParentToken =
+      LoopStack.hasInfo()
+          ? getOrEmitConvergenceLoopToken(&LoopStack.getInfo())
+          : getOrEmitConvergenceEntryToken(Input->getFunction());
+  return AddConvergenceControlAttr(Input, ParentToken);
+}
+
 BitTest BitTest::decodeBitTestBuiltin(unsigned BuiltinID) {
   switch (BuiltinID) {
     // Main portable variants.
@@ -5696,6 +5785,19 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
         {NDRange, Kernel, Block}));
   }
 
+  case Builtin::BI__builtin_hlsl_wave_active_count_bits: {
+    llvm::Type *BoolTy = llvm::IntegerType::get(getLLVMContext(), 1);
+    llvm::Value *Src0 = EmitScalarExpr(E->getArg(0));
+    auto *CI =
+        EmitRuntimeCall(CGM.CreateRuntimeFunction(
+                            llvm::FunctionType::get(IntTy, {BoolTy}, false),
+                            "__hlsl_wave_active_count_bits", {}),
+                        {Src0});
+    if (getTarget().getTriple().isSPIRVLogical())
+      CI = dyn_cast<CallInst>(AddControlledConvergenceAttr(CI));
+    return RValue::get(CI);
+  }
+
   case Builtin::BI__builtin_store_half:
   case Builtin::BI__builtin_store_halff: {
     Value *Val = EmitScalarExpr(E->getArg(0));
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index d05cf1c6e1814e..53c39f7b6b3cb7 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -5687,6 +5687,10 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
   if (!CI->getType()->isVoidTy())
     CI->setName("call");
 
+  if (getTarget().getTriple().isSPIRVLogical() &&
+      CI->getCalledFunction()->isConvergent())
+    CI = AddControlledConvergenceAttr(CI);
+
   // Update largest vector width from the return type.
   LargestVectorWidth =
       std::max(LargestVectorWidth, getMaxVectorWidth(CI->getType()));
diff --git a/clang/lib/CodeGen/CGLoopInfo.h b/clang/lib/CodeGen/CGLoopInfo.h
index a1c8c7e5307fd9..7c2f7443bd3c99 100644
--- a/clang/lib/CodeGen/CGLoopInfo.h
+++ b/clang/lib/CodeGen/CGLoopInfo.h
@@ -110,6 +110,10 @@ class LoopInfo {
   /// been processed.
   void finish();
 
+  /// Returns the first outer loop containing this loop if any, nullptr
+  /// otherwise.
+  const LoopInfo *getParent() const { return Parent; }
+
 private:
   /// Loop ID metadata.
   llvm::TempMDTuple TempLoopID;
@@ -291,12 +295,14 @@ class LoopInfoStack {
   /// Set no progress for the next loop pushed.
   void setMustProgress(bool P) { StagedAttrs.MustProgress = P; }
 
-private:
   /// Returns true if there is LoopInfo on the stack.
   bool hasInfo() const { return !Active.empty(); }
+
   /// Return the LoopInfo for the current loop. HasInfo should be called
   /// first to ensure LoopInfo is present.
   const LoopInfo &getInfo() const { return *Active.back(); }
+
+private:
   /// The set of attributes that will be applied to the next pushed loop.
   LoopAttributes StagedAttrs;
   /// Stack of active loops.
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index caa6a327550baa..21c269ac64e46d 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -4154,6 +4154,25 @@ class CodeGenFunction : public CodeGenTypeCache {
   void checkTargetFeatures(const CallExpr *E, const FunctionDecl *TargetDecl);
   void checkTargetFeatures(SourceLocation Loc, const FunctionDecl *TargetDecl);
 
+  // Adds a convergence_ctrl attribute to |Input| and emits the required parent
+  // convergence instructions.
+  llvm::CallBase *AddControlledConvergenceAttr(llvm::CallBase *Input);
+
+  // Emits a convergence_loop instruction for the given |BB|, with |ParentToken|
+  // as it's parent convergence instr.
+  llvm::IntrinsicInst *EmitConvergenceLoop(llvm::BasicBlock *BB,
+                                           llvm::Value *ParentToken);
+  // Adds a convergence_ctrl attribute with |ParentToken| as parent convergence
+  // instr to the call |Input|.
+  llvm::CallBase *AddConvergenceControlAttr(llvm::CallBase *Input,
+                                            llvm::Value *ParentToken);
+  // Find the convergence_entry instruction |F|, or emits ones if none exists.
+  // Returns the convergence instruction.
+  llvm::IntrinsicInst *getOrEmitConvergenceEntryToken(llvm::Function *F);
+  // Find the convergence_loop instruction for the loop defined by |LI|, or
+  // emits one if none exists. Returns the convergence instruction.
+  llvm::IntrinsicInst *getOrEmitConvergenceLoopToken(const LoopInfo *LI);
+
   llvm::CallInst *EmitRuntimeCall(llvm::FunctionCallee callee,
                                   const Twine &name = "");
   llvm::CallInst *EmitRuntimeCall(llvm::FunctionCallee callee,
diff --git a/llvm/include/llvm/IR/IntrinsicInst.h b/llvm/include/llvm/IR/IntrinsicInst.h
index b8d578d0fee082..c0c19203b160a4 100644
--- a/llvm/include/llvm/IR/IntrinsicInst.h
+++ b/llvm/include/llvm/IR/IntrinsicInst.h
@@ -1746,6 +1746,19 @@ class ConvergenceControlInst : public IntrinsicInst {
   static bool classof(const Value *V) {
     return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
   }
+
+  // Returns the convergence intrinsic referenced by |I|'s convergencectrl
+  // attribute if any.
+  static IntrinsicInst *getParentConvergenceToken(Instruction *I) {
+    auto *CI = dyn_cast<llvm::CallInst>(I);
+    if (!CI)
+      return nullptr;
+
+    auto Bundle = CI->getOperandBundle(llvm::LLVMContext::OB_convergencectrl);
+    assert(Bundle->Inputs.size() == 1 &&
+           Bundle->Inputs[0]->getType()->isTokenTy());
+    return dyn_cast<llvm::IntrinsicInst>(Bundle->Inputs[0].get());
+  }
 };
 
 } // end namespace llvm

>From 55509e5057cff4292a400f510f8c4a3451ac6641 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nathan=20Gau=C3=ABr?= <brioche at google.com>
Date: Thu, 22 Feb 2024 20:39:40 +0100
Subject: [PATCH 2/2] change implemented builtin
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Signed-off-by: Nathan Gauër <brioche at google.com>
---
 clang/include/clang/Basic/Builtins.td    |  7 +++++++
 clang/lib/CodeGen/CGBuiltin.cpp          | 18 +++++++-----------
 clang/lib/Headers/hlsl/hlsl_intrinsics.h |  5 +++++
 3 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/clang/include/clang/Basic/Builtins.td b/clang/include/clang/Basic/Builtins.td
index df74026c5d2d50..68ec2e50f5219e 100644
--- a/clang/include/clang/Basic/Builtins.td
+++ b/clang/include/clang/Basic/Builtins.td
@@ -4518,6 +4518,13 @@ def HLSLWaveActiveCountBits : LangBuiltin<"HLSL_LANG"> {
   let Prototype = "unsigned int(bool)";
 }
 
+// HLSL
+def HLSLWaveGetLaneIndex : LangBuiltin<"HLSL_LANG"> {
+  let Spellings = ["__builtin_hlsl_wave_get_lane_index"];
+  let Attributes = [NoThrow, Const];
+  let Prototype = "unsigned int()";
+}
+
 def HLSLCreateHandle : LangBuiltin<"HLSL_LANG"> {
   let Spellings = ["__builtin_hlsl_create_handle"];
   let Attributes = [NoThrow, Const];
diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index 82e652959238b4..73baf23c012335 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -1169,8 +1169,7 @@ CodeGenFunction::EmitConvergenceLoop(llvm::BasicBlock *BB,
   // Removing any old attributes.
   I->setNotConvergent();
 
-  assert(isa<llvm::IntrinsicInst>(I));
-  return dyn_cast<llvm::IntrinsicInst>(I);
+  return cast<llvm::IntrinsicInst>(I);
 }
 
 llvm::IntrinsicInst *
@@ -1191,7 +1190,7 @@ CodeGenFunction::getOrEmitConvergenceEntryToken(llvm::Function *F) {
   assert(isa<llvm::IntrinsicInst>(I));
   Builder.restoreIP(IP);
 
-  return dyn_cast<llvm::IntrinsicInst>(I);
+  return cast<llvm::IntrinsicInst>(I);
 }
 
 llvm::IntrinsicInst *
@@ -5785,14 +5784,11 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
         {NDRange, Kernel, Block}));
   }
 
-  case Builtin::BI__builtin_hlsl_wave_active_count_bits: {
-    llvm::Type *BoolTy = llvm::IntegerType::get(getLLVMContext(), 1);
-    llvm::Value *Src0 = EmitScalarExpr(E->getArg(0));
-    auto *CI =
-        EmitRuntimeCall(CGM.CreateRuntimeFunction(
-                            llvm::FunctionType::get(IntTy, {BoolTy}, false),
-                            "__hlsl_wave_active_count_bits", {}),
-                        {Src0});
+  case Builtin::BI__builtin_hlsl_wave_get_lane_index: {
+    // llvm::Value *Src0 = EmitScalarExpr(E->getArg(0));
+    auto *CI = EmitRuntimeCall(CGM.CreateRuntimeFunction(
+        llvm::FunctionType::get(IntTy, {}, false), "__hlsl_wave_get_lane_index",
+        {}, false, true));
     if (getTarget().getTriple().isSPIRVLogical())
       CI = dyn_cast<CallInst>(AddControlledConvergenceAttr(CI));
     return RValue::get(CI);
diff --git a/clang/lib/Headers/hlsl/hlsl_intrinsics.h b/clang/lib/Headers/hlsl/hlsl_intrinsics.h
index f87ac977997962..79186c1e49fb86 100644
--- a/clang/lib/Headers/hlsl/hlsl_intrinsics.h
+++ b/clang/lib/Headers/hlsl/hlsl_intrinsics.h
@@ -775,5 +775,10 @@ _HLSL_AVAILABILITY(shadermodel, 6.0)
 _HLSL_BUILTIN_ALIAS(__builtin_hlsl_wave_active_count_bits)
 uint WaveActiveCountBits(bool Val);
 
+/// \brief Returns the index of the current lane within the current wave.
+_HLSL_AVAILABILITY(shadermodel, 6.0)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_wave_get_lane_index)
+uint WaveGetLaneIndex();
+
 } // namespace hlsl
 #endif //_HLSL_HLSL_INTRINSICS_H_



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