From 281d20b601c8a2a77b9eac458cafb0482fa94c88 Mon Sep 17 00:00:00 2001
From: Erich Keane <erich.keane@intel.com>
Date: Mon, 8 Jan 2018 21:34:17 +0000
Subject: Implement Attribute Target MultiVersioning

GCC's attribute 'target', in addition to being an optimization hint,
also allows function multiversioning. We currently have the former
implemented, this is the latter's implementation.

This works by enabling functions with the same name/signature to coexist,
so that they can all be emitted. Multiversion state is stored in the
FunctionDecl itself, and SemaDecl manages the definitions.
Note that it ends up having to permit redefinition of functions so
that they can all be emitted. Additionally, all versions of the function
must be emitted, so this also manages that.

Note that this includes some additional rules that GCC does not, since
defining something as a MultiVersion function after a usage has been made illegal.

The only 'history rewriting' that happens is if a function is emitted before
it has been converted to a multiversion'ed function, at which point its name
needs to be changed.

Function templates and virtual functions are NOT yet supported (not supported
in GCC either).

Additionally, constructors/destructors are disallowed, but the former is
planned.

llvm-svn: 322028
---
 clang/lib/CodeGen/CodeGenFunction.cpp | 54 +++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

(limited to 'clang/lib/CodeGen/CodeGenFunction.cpp')

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 6fb21b157367..0cbe071d1b93 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -2305,6 +2305,60 @@ void CodeGenFunction::EmitSanitizerStatReport(llvm::SanitizerStatKind SSK) {
   CGM.getSanStats().create(IRB, SSK);
 }
 
+llvm::Value *
+CodeGenFunction::FormResolverCondition(const MultiVersionResolverOption &RO) {
+  llvm::Value *TrueCondition = nullptr;
+  if (!RO.ParsedAttribute.Architecture.empty())
+    TrueCondition = EmitX86CpuIs(RO.ParsedAttribute.Architecture);
+
+  if (!RO.ParsedAttribute.Features.empty()) {
+    SmallVector<StringRef, 8> FeatureList;
+    llvm::for_each(RO.ParsedAttribute.Features,
+                   [&FeatureList](const std::string &Feature) {
+                     FeatureList.push_back(StringRef{Feature}.substr(1));
+                   });
+    llvm::Value *FeatureCmp = EmitX86CpuSupports(FeatureList);
+    TrueCondition = TrueCondition ? Builder.CreateAnd(TrueCondition, FeatureCmp)
+                                  : FeatureCmp;
+  }
+  return TrueCondition;
+}
+
+void CodeGenFunction::EmitMultiVersionResolver(
+    llvm::Function *Resolver, ArrayRef<MultiVersionResolverOption> Options) {
+  assert((getContext().getTargetInfo().getTriple().getArch() ==
+              llvm::Triple::x86 ||
+          getContext().getTargetInfo().getTriple().getArch() ==
+              llvm::Triple::x86_64) &&
+         "Only implemented for x86 targets");
+
+  // Main function's basic block.
+  llvm::BasicBlock *CurBlock = createBasicBlock("entry", Resolver);
+  Builder.SetInsertPoint(CurBlock);
+  EmitX86CpuInit();
+
+  llvm::Function *DefaultFunc = nullptr;
+  for (const MultiVersionResolverOption &RO : Options) {
+    Builder.SetInsertPoint(CurBlock);
+    llvm::Value *TrueCondition = FormResolverCondition(RO);
+
+    if (!TrueCondition) {
+      DefaultFunc = RO.Function;
+    } else {
+      llvm::BasicBlock *RetBlock = createBasicBlock("ro_ret", Resolver);
+      llvm::IRBuilder<> RetBuilder(RetBlock);
+      RetBuilder.CreateRet(RO.Function);
+      CurBlock = createBasicBlock("ro_else", Resolver);
+      Builder.CreateCondBr(TrueCondition, RetBlock, CurBlock);
+    }
+  }
+
+  assert(DefaultFunc && "No default version?");
+  // Emit return from the 'else-ist' block.
+  Builder.SetInsertPoint(CurBlock);
+  Builder.CreateRet(DefaultFunc);
+}
+
 llvm::DebugLoc CodeGenFunction::SourceLocToDebugLoc(SourceLocation Location) {
   if (CGDebugInfo *DI = getDebugInfo())
     return DI->SourceLocToDebugLoc(Location);
-- 
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