[PATCH] Add support for __nvvm_reflect changes in libdevice in CUDA-7.0

[Artem Belevich]

Added details on the differences in IR used to call __nvvm_reflect in different CUDA versions.
Updated IR in the test case to work with recent LLVM.


http://reviews.llvm.org/D8399

Files:
  lib/Target/NVPTX/NVVMReflect.cpp
  test/CodeGen/NVPTX/nvvm-reflect.ll

Index: lib/Target/NVPTX/NVVMReflect.cpp
===================================================================
--- lib/Target/NVPTX/NVVMReflect.cpp
+++ lib/Target/NVPTX/NVVMReflect.cpp
@@ -137,6 +137,26 @@
   // ConstantArray can be found successfully, see if it can be
   // found in VarMap. If so, replace the uses of CallInst with the
   // value found in VarMap. If not, replace the use  with value 0.
+
+  // IR for __nvvm_reflect calls differs between CUDA versions:
+  // CUDA 6.5 and earlier uses this sequence:
+  //    %ptr = tail call i8* @llvm.nvvm.ptr.constant.to.gen.p0i8.p4i8
+  //        (i8 addrspace(4)* getelementptr inbounds
+  //           ([8 x i8], [8 x i8] addrspace(4)* @str, i32 0, i32 0))
+  //    %reflect = tail call i32 @__nvvm_reflect(i8* %ptr)
+  //
+  // Value returned by Sym->getOperand(0) is a Constant with a
+  // ConstantDataSequential operand which can be converted to string and used
+  // for lookup.
+  //
+  // CUDA 7.0 does it slightly differently:
+  //   %reflect = call i32 @__nvvm_reflect(i8* addrspacecast
+  //        (i8 addrspace(1)* getelementptr inbounds
+  //           ([8 x i8], [8 x i8] addrspace(1)* @str, i32 0, i32 0) to i8*))
+  //
+  // In this case, we get a Constant with a GlobalVariable operand and we need
+  // to dig deeper to find its initializer with the string we'll use for lookup.
+
   for (User *U : ReflectFunction->users()) {
     assert(isa<CallInst>(U) && "Only a call instruction can use _reflect");
     CallInst *Reflect = cast<CallInst>(U);
@@ -158,16 +178,24 @@
     const Value *Sym = GEP->getOperand(0);
     assert(isa<Constant>(Sym) && "Format of _reflect function not recognized");
 
-    const Constant *SymStr = cast<Constant>(Sym);
+    const Value *Operand = cast<Constant>(Sym)->getOperand(0);
+    if (isa<GlobalVariable>(Operand)) {
+      // For CUDA-7.0 style __nvvm_reflect calls we need to find operand's
+      // initializer.
+      assert(cast<GlobalVariable>(Operand)->hasInitializer() &&
+             "Format of _reflect function not recognized");
+      const Constant *Initializer =
+          cast<GlobalVariable>(Operand)->getInitializer();
+      Operand = Initializer;
+    }
 
-    assert(isa<ConstantDataSequential>(SymStr->getOperand(0)) &&
+    assert(isa<ConstantDataSequential>(Operand) &&
            "Format of _reflect function not recognized");
-
-    assert(cast<ConstantDataSequential>(SymStr->getOperand(0))->isCString() &&
+    assert(cast<ConstantDataSequential>(Operand)->isCString() &&
            "Format of _reflect function not recognized");
 
     std::string ReflectArg =
-        cast<ConstantDataSequential>(SymStr->getOperand(0))->getAsString();
+        cast<ConstantDataSequential>(Operand)->getAsString();
 
     ReflectArg = ReflectArg.substr(0, ReflectArg.size() - 1);
     DEBUG(dbgs() << "Arg of _reflect : " << ReflectArg << "\n");
Index: test/CodeGen/NVPTX/nvvm-reflect.ll
===================================================================
--- test/CodeGen/NVPTX/nvvm-reflect.ll
+++ test/CodeGen/NVPTX/nvvm-reflect.ll
@@ -46,3 +46,31 @@
   %reflect = tail call i32 @llvm.nvvm.reflect.p0i8(i8* %ptr)
   ret i32 %reflect
 }
+
+@"$str" = private addrspace(1) constant [8 x i8] c"USE_MUL\00"
+
+define float @bar(float %a, float %b) {
+; USE_MUL_0: define float @bar
+; USE_MUL_0-NOT: call i32 @__nvvm_reflect
+; USE_MUL_1: define float @bar
+; USE_MUL_1-NOT: call i32 @__nvvm_reflect
+  %reflect = call i32 @__nvvm_reflect(i8* addrspacecast (i8 addrspace(1)* getelementptr inbounds ([8 x i8], [8 x i8] addrspace(1)* @"$str", i32 0, i32 0) to i8*))
+  %cmp = icmp ne i32 %reflect, 0
+  br i1 %cmp, label %use_mul, label %use_add
+
+use_mul:
+; USE_MUL_1: fmul float %a, %b
+; USE_MUL_0-NOT: fadd float %a, %b
+  %ret1 = fmul float %a, %b
+  br label %exit
+
+use_add:
+; USE_MUL_0: fadd float %a, %b
+; USE_MUL_1-NOT: fmul float %a, %b
+  %ret2 = fadd float %a, %b
+  br label %exit
+
+exit:
+  %ret = phi float [%ret1, %use_mul], [%ret2, %use_add]
+  ret float %ret
+}

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