Implement cpu_dispatch/cpu_specific Multiversioning

As documented here: https://software.intel.com/en-us/node/682969 and
https://software.intel.com/en-us/node/523346. cpu_dispatch multiversioning
is an ICC feature that provides for function multiversioning.

This feature is implemented with two attributes: First, cpu_specific,
which specifies the individual function versions. Second, cpu_dispatch,
which specifies the location of the resolver function and the list of
resolvable functions.

This is valuable since it provides a mechanism where the resolver's TU
can be specified in one location, and the individual implementions
each in their own translation units.

The goal of this patch is to be source-compatible with ICC, so this
implementation diverges from the ICC implementation in a few ways:
1- Linux x86/64 only: This implementation uses ifuncs in order to
properly dispatch functions. This is is a valuable performance benefit
over the ICC implementation. A future patch will be provided to enable
this feature on Windows, but it will obviously more closely fit ICC's
implementation.
2- CPU Identification functions: ICC uses a set of custom functions to identify
the feature list of the host processor. This patch uses the cpu_supports
functionality in order to better align with 'target' multiversioning.
1- cpu_dispatch function def/decl: ICC's cpu_dispatch requires that the function
marked cpu_dispatch be an empty definition. This patch supports that as well,
however declarations are also permitted, since the linker will solve the
issue of multiple emissions.

Differential Revision: https://reviews.llvm.org/D47474


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@337552 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 35 insertions, 11 deletions

diff --git a/lib/Sema/Sema.cpp b/lib/Sema/Sema.cpp
index f81a34c40b..d57473c561 100644
--- a/lib/Sema/Sema.cpp
+++ b/lib/Sema/Sema.cpp
@@ -1585,6 +1585,7 @@ bool Sema::tryExprAsCall(Expr &E, QualType &ZeroArgCallReturnTy,
   }
 
   bool Ambiguous = false;
+  bool IsMV = false;
 
   if (Overloads) {
     for (OverloadExpr::decls_iterator it = Overloads->decls_begin(),
@@ -1598,11 +1599,16 @@ bool Sema::tryExprAsCall(Expr &E, QualType &ZeroArgCallReturnTy,
       if (const FunctionDecl *OverloadDecl
             = dyn_cast<FunctionDecl>((*it)->getUnderlyingDecl())) {
         if (OverloadDecl->getMinRequiredArguments() == 0) {
-          if (!ZeroArgCallReturnTy.isNull() && !Ambiguous) {
+          if (!ZeroArgCallReturnTy.isNull() && !Ambiguous &&
+              (!IsMV || !(OverloadDecl->isCPUDispatchMultiVersion() ||
+                          OverloadDecl->isCPUSpecificMultiVersion()))) {
             ZeroArgCallReturnTy = QualType();
             Ambiguous = true;
-          } else
+          } else {
             ZeroArgCallReturnTy = OverloadDecl->getReturnType();
+            IsMV = OverloadDecl->isCPUDispatchMultiVersion() ||
+                   OverloadDecl->isCPUSpecificMultiVersion();
+          }
         }
       }
     }
@@ -1683,7 +1689,7 @@ static void noteOverloads(Sema &S, const UnresolvedSetImpl &Overloads,
     NamedDecl *Fn = (*It)->getUnderlyingDecl();
     // Don't print overloads for non-default multiversioned functions.
     if (const auto *FD = Fn->getAsFunction()) {
-      if (FD->isMultiVersion() &&
+      if (FD->isMultiVersion() && FD->hasAttr<TargetAttr>() &&
           !FD->getAttr<TargetAttr>()->isDefaultVersion())
         continue;
     }
@@ -1725,6 +1731,21 @@ static bool IsCallableWithAppend(Expr *E) {
           !isa<CXXOperatorCallExpr>(E));
 }
 
+static bool IsCPUDispatchCPUSpecificMultiVersion(const Expr *E) {
+  if (const auto *UO = dyn_cast<UnaryOperator>(E))
+    E = UO->getSubExpr();
+
+  if (const auto *ULE = dyn_cast<UnresolvedLookupExpr>(E)) {
+    if (ULE->getNumDecls() == 0)
+      return false;
+
+    const NamedDecl *ND = *ULE->decls_begin();
+    if (const auto *FD = dyn_cast<FunctionDecl>(ND))
+      return FD->isCPUDispatchMultiVersion() || FD->isCPUSpecificMultiVersion();
+  }
+  return false;
+}
+
 bool Sema::tryToRecoverWithCall(ExprResult &E, const PartialDiagnostic &PD,
                                 bool ForceComplain,
                                 bool (*IsPlausibleResult)(QualType)) {
@@ -1741,12 +1762,13 @@ bool Sema::tryToRecoverWithCall(ExprResult &E, const PartialDiagnostic &PD,
     // so we can emit a fixit and carry on pretending that E was
     // actually a CallExpr.
     SourceLocation ParenInsertionLoc = getLocForEndOfToken(Range.getEnd());
-    Diag(Loc, PD)
-      << /*zero-arg*/ 1 << Range
-      << (IsCallableWithAppend(E.get())
-          ? FixItHint::CreateInsertion(ParenInsertionLoc, "()")
-          : FixItHint());
-    notePlausibleOverloads(*this, Loc, Overloads, IsPlausibleResult);
+    bool IsMV = IsCPUDispatchCPUSpecificMultiVersion(E.get());
+    Diag(Loc, PD) << /*zero-arg*/ 1 << IsMV << Range
+                  << (IsCallableWithAppend(E.get())
+                          ? FixItHint::CreateInsertion(ParenInsertionLoc, "()")
+                          : FixItHint());
+    if (!IsMV)
+      notePlausibleOverloads(*this, Loc, Overloads, IsPlausibleResult);
 
     // FIXME: Try this before emitting the fixit, and suppress diagnostics
     // while doing so.
@@ -1757,8 +1779,10 @@ bool Sema::tryToRecoverWithCall(ExprResult &E, const PartialDiagnostic &PD,
 
   if (!ForceComplain) return false;
 
-  Diag(Loc, PD) << /*not zero-arg*/ 0 << Range;
-  notePlausibleOverloads(*this, Loc, Overloads, IsPlausibleResult);
+  bool IsMV = IsCPUDispatchCPUSpecificMultiVersion(E.get());
+  Diag(Loc, PD) << /*not zero-arg*/ 0 << IsMV << Range;
+  if (!IsMV)
+    notePlausibleOverloads(*this, Loc, Overloads, IsPlausibleResult);
   E = ExprError();
   return true;
 }