[OpenMP][NVPTX][CUDA] Adding support for printf for an NVPTX OpenMP device.

Support for CUDA printf is exploited to support printf for
an NVPTX OpenMP device.

To reflect the support of both programming models, the file
CGCUDABuiltin.cpp has been renamed to CGGPUBuiltin.cpp, and
the call EmitCUDADevicePrintfCallExpr has been renamed to
EmitGPUDevicePrintfCallExpr.

Reviewers: jlebar
Differential Revision: https://reviews.llvm.org/D17890

llvm-svn: 293444

1 files changed, 122 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGGPUBuiltin.cpp b/clang/lib/CodeGen/CGGPUBuiltin.cpp
new file mode 100644
index 00000000000..48156b1b26b
--- /dev/null
+++ b/clang/lib/CodeGen/CGGPUBuiltin.cpp
@@ -0,0 +1,122 @@
+//===------ CGGPUBuiltin.cpp - Codegen for GPU builtins -------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Generates code for built-in GPU calls which are not runtime-specific.
+// (Runtime-specific codegen lives in programming model specific files.)
+//
+//===----------------------------------------------------------------------===//
+
+#include "CodeGenFunction.h"
+#include "clang/Basic/Builtins.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/Support/MathExtras.h"
+
+using namespace clang;
+using namespace CodeGen;
+
+static llvm::Function *GetVprintfDeclaration(llvm::Module &M) {
+  llvm::Type *ArgTypes[] = {llvm::Type::getInt8PtrTy(M.getContext()),
+                            llvm::Type::getInt8PtrTy(M.getContext())};
+  llvm::FunctionType *VprintfFuncType = llvm::FunctionType::get(
+      llvm::Type::getInt32Ty(M.getContext()), ArgTypes, false);
+
+  if (auto* F = M.getFunction("vprintf")) {
+    // Our CUDA system header declares vprintf with the right signature, so
+    // nobody else should have been able to declare vprintf with a bogus
+    // signature.
+    assert(F->getFunctionType() == VprintfFuncType);
+    return F;
+  }
+
+  // vprintf doesn't already exist; create a declaration and insert it into the
+  // module.
+  return llvm::Function::Create(
+      VprintfFuncType, llvm::GlobalVariable::ExternalLinkage, "vprintf", &M);
+}
+
+// Transforms a call to printf into a call to the NVPTX vprintf syscall (which
+// isn't particularly special; it's invoked just like a regular function).
+// vprintf takes two args: A format string, and a pointer to a buffer containing
+// the varargs.
+//
+// For example, the call
+//
+//   printf("format string", arg1, arg2, arg3);
+//
+// is converted into something resembling
+//
+//   struct Tmp {
+//     Arg1 a1;
+//     Arg2 a2;
+//     Arg3 a3;
+//   };
+//   char* buf = alloca(sizeof(Tmp));
+//   *(Tmp*)buf = {a1, a2, a3};
+//   vprintf("format string", buf);
+//
+// buf is aligned to the max of {alignof(Arg1), ...}.  Furthermore, each of the
+// args is itself aligned to its preferred alignment.
+//
+// Note that by the time this function runs, E's args have already undergone the
+// standard C vararg promotion (short -> int, float -> double, etc.).
+RValue
+CodeGenFunction::EmitNVPTXDevicePrintfCallExpr(const CallExpr *E,
+                                               ReturnValueSlot ReturnValue) {
+  assert(getTarget().getTriple().isNVPTX());
+  assert(E->getBuiltinCallee() == Builtin::BIprintf);
+  assert(E->getNumArgs() >= 1); // printf always has at least one arg.
+
+  const llvm::DataLayout &DL = CGM.getDataLayout();
+  llvm::LLVMContext &Ctx = CGM.getLLVMContext();
+
+  CallArgList Args;
+  EmitCallArgs(Args,
+               E->getDirectCallee()->getType()->getAs<FunctionProtoType>(),
+               E->arguments(), E->getDirectCallee(),
+               /* ParamsToSkip = */ 0);
+
+  // We don't know how to emit non-scalar varargs.
+  if (std::any_of(Args.begin() + 1, Args.end(),
+                  [](const CallArg &A) { return !A.RV.isScalar(); })) {
+    CGM.ErrorUnsupported(E, "non-scalar arg to printf");
+    return RValue::get(llvm::ConstantInt::get(IntTy, 0));
+  }
+
+  // Construct and fill the args buffer that we'll pass to vprintf.
+  llvm::Value *BufferPtr;
+  if (Args.size() <= 1) {
+    // If there are no args, pass a null pointer to vprintf.
+    BufferPtr = llvm::ConstantPointerNull::get(llvm::Type::getInt8PtrTy(Ctx));
+  } else {
+    llvm::SmallVector<llvm::Type *, 8> ArgTypes;
+    for (unsigned I = 1, NumArgs = Args.size(); I < NumArgs; ++I)
+      ArgTypes.push_back(Args[I].RV.getScalarVal()->getType());
+
+    // Using llvm::StructType is correct only because printf doesn't accept
+    // aggregates.  If we had to handle aggregates here, we'd have to manually
+    // compute the offsets within the alloca -- we wouldn't be able to assume
+    // that the alignment of the llvm type was the same as the alignment of the
+    // clang type.
+    llvm::Type *AllocaTy = llvm::StructType::create(ArgTypes, "printf_args");
+    llvm::Value *Alloca = CreateTempAlloca(AllocaTy);
+
+    for (unsigned I = 1, NumArgs = Args.size(); I < NumArgs; ++I) {
+      llvm::Value *P = Builder.CreateStructGEP(AllocaTy, Alloca, I - 1);
+      llvm::Value *Arg = Args[I].RV.getScalarVal();
+      Builder.CreateAlignedStore(Arg, P, DL.getPrefTypeAlignment(Arg->getType()));
+    }
+    BufferPtr = Builder.CreatePointerCast(Alloca, llvm::Type::getInt8PtrTy(Ctx));
+  }
+
+  // Invoke vprintf and return.
+  llvm::Function* VprintfFunc = GetVprintfDeclaration(CGM.getModule());
+  return RValue::get(
+      Builder.CreateCall(VprintfFunc, {Args[0].RV.getScalarVal(), BufferPtr}));
+}