[NVPTX] Read __CUDA_FTZ from module flags in NVVMReflect.

Summary:
Previously the NVVMReflect pass would read its configuration from
command-line flags or a static configuration given to the pass at
instantiation time.

This doesn't quite work for clang's use-case.  It needs to pass a value
for __CUDA_FTZ down on a per-module basis.  We use a module flag for
this, so the NVVMReflect pass needs to be updated to read said flag.

Reviewers: tra, rnk

Subscribers: cfe-commits, jholewinski

Differential Revision: http://reviews.llvm.org/D18672

llvm-svn: 265090

llvm/lib/Target/NVPTX/NVVMReflect.cpp

@@ -7,11 +7,16 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// This pass replaces occurrences of __nvvm_reflect("string") and
+// This pass replaces occurrences of __nvvm_reflect("foo") and llvm.nvvm.reflect
-// llvm.nvvm.reflect with an integer based on the value of -nvvm-reflect-list
+// with an integer.
-// string=<int>.
 //
-// If we see a string not specified in our flags, we replace that call with 0.
+// We choose the value we use by looking, in this order, at:
+//
+//  * the -nvvm-reflect-list flag, which has the format "foo=1,bar=42",
+//  * the StringMap passed to the pass's constructor, and
+//  * metadata in the module itself.
+//
+// If we see an unknown string, we replace its call with 0.
 //
 //===----------------------------------------------------------------------===//
 
@@ -55,10 +60,9 @@ public:
   static char ID;
   NVVMReflect() : NVVMReflect(StringMap<int>()) {}
 
-  NVVMReflect(const StringMap<int> &Mapping) : FunctionPass(ID) {
+  NVVMReflect(const StringMap<int> &Mapping)
+      : FunctionPass(ID), VarMap(Mapping) {
     initializeNVVMReflectPass(*PassRegistry::getPassRegistry());
-    for (const auto &KV : Mapping)
-      VarMap[KV.getKey()] = KV.getValue();
     setVarMap();
   }
 
@@ -206,6 +210,12 @@ bool NVVMReflect::runOnFunction(Function &F) {
     auto Iter = VarMap.find(ReflectArg);
     if (Iter != VarMap.end())
       ReflectVal = Iter->second;
+    else if (ReflectArg == "__CUDA_FTZ") {
+      // Try to pull __CUDA_FTZ from the nvvm-reflect-ftz module flag.
+      if (auto *Flag = mdconst::extract_or_null<ConstantInt>(
+              F.getParent()->getModuleFlag("nvvm-reflect-ftz")))
+        ReflectVal = Flag->getSExtValue();
+    }
     Call->replaceAllUsesWith(ConstantInt::get(Call->getType(), ReflectVal));
     ToRemove.push_back(Call);
   }

llvm/test/CodeGen/NVPTX/nvvm-reflect-module-flag.ll

@@ -0,0 +1,13 @@
+; RUN: opt < %s -S -nvvm-reflect | FileCheck %s
+
+declare i32 @__nvvm_reflect(i8*)
+@str = private unnamed_addr addrspace(1) constant [11 x i8] c"__CUDA_FTZ\00"
+
+define i32 @foo() {
+  %call = call i32 @__nvvm_reflect(i8* addrspacecast (i8 addrspace(1)* getelementptr inbounds ([11 x i8], [11 x i8] addrspace(1)* @str, i32 0, i32 0) to i8*))
+  ; CHECK: ret i32 42
+  ret i32 %call
+}
+
+!llvm.module.flags = !{!0}
+!0 = !{i32 4, !"nvvm-reflect-ftz", i32 42}