[SIL] Get access to LLVM intrinsic attributes.

And use them to decide if an llvm intrinsic apply instruction can be considered dead.

(This is a hack because it uses LLVM Global context. However, we already use
this approach elsewhere.)

Swift SVN r7404

Author: AnnaZaks

include/swift/AST/Builtins.h

@@ -19,6 +19,7 @@
 
 #include "swift/Basic/LLVM.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/IR/Attributes.h"
 #include "swift/AST/Type.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -96,6 +97,7 @@ struct BuiltinInfo {
 struct IntrinsicInfo {
   llvm::Intrinsic::ID ID;
   SmallVector<Type, 4> Types;
+  bool hasAttribute(llvm::Attribute::AttrKind Kind) const;
 };
 
 }

lib/AST/Builtins.cpp

@@ -39,6 +39,13 @@ bool BuiltinInfo::isReadNone() const {
   return strchr(BuiltinExtraInfo[(unsigned)ID].Attributes, 'n') != 0;
 }
 
+bool IntrinsicInfo::hasAttribute(llvm::Attribute::AttrKind Kind) const {
+  // FIXME: We should not be relying on the global LLVM context.
+  llvm::AttributeSet attrs
+    = llvm::Intrinsic::getAttributes(llvm::getGlobalContext(), ID);
+  return (attrs.hasAttribute(llvm::AttributeSet::FunctionIndex, Kind));
+}
+
 Type swift::getBuiltinType(ASTContext &Context, StringRef Name) {
   // Vectors are VecNxT, where "N" is the number of elements and
   // T is the element type.

lib/SILPasses/Utils/Local.cpp

@@ -17,51 +17,19 @@ using namespace swift;
 static bool isSideEffectFree(BuiltinFunctionRefInst *FR) {
 
   // First, check if we are dealing with a swift builtin.
-  const BuiltinInfo &Info = FR->getBuiltinInfo();
-  if (Info.ID != BuiltinValueKind::None) {
-    return Info.isReadNone();
+  const BuiltinInfo &BInfo = FR->getBuiltinInfo();
+  if (BInfo.ID != BuiltinValueKind::None) {
+    return BInfo.isReadNone();
   }
 
   // Second, specialcase llvm intrinsic.
-  // FIXME: This list might not be complete. Would be good to derive this
-  // info from llvm.
-  switch (FR->getIntrinsicInfo().ID) {
-    default:
-      return false;
-    case llvm::Intrinsic::fabs:
-    case llvm::Intrinsic::log:
-    case llvm::Intrinsic::log2:
-    case llvm::Intrinsic::log10:
-    case llvm::Intrinsic::exp:
-    case llvm::Intrinsic::exp2:
-    case llvm::Intrinsic::floor:
-    case llvm::Intrinsic::sqrt:
-    case llvm::Intrinsic::pow:
-    case llvm::Intrinsic::powi:
-    case llvm::Intrinsic::bswap:
-    case llvm::Intrinsic::ctpop:
-    case llvm::Intrinsic::ctlz:
-    case llvm::Intrinsic::cttz:
-    case llvm::Intrinsic::sadd_with_overflow:
-    case llvm::Intrinsic::uadd_with_overflow:
-    case llvm::Intrinsic::ssub_with_overflow:
-    case llvm::Intrinsic::usub_with_overflow:
-    case llvm::Intrinsic::smul_with_overflow:
-    case llvm::Intrinsic::umul_with_overflow:
-    case llvm::Intrinsic::convert_from_fp16:
-    case llvm::Intrinsic::convert_to_fp16:
-    case llvm::Intrinsic::x86_sse_cvtss2si:
-    case llvm::Intrinsic::x86_sse_cvtss2si64:
-    case llvm::Intrinsic::x86_sse_cvttss2si:
-    case llvm::Intrinsic::x86_sse_cvttss2si64:
-    case llvm::Intrinsic::x86_sse2_cvtsd2si:
-    case llvm::Intrinsic::x86_sse2_cvtsd2si64:
-    case llvm::Intrinsic::x86_sse2_cvttsd2si:
-    case llvm::Intrinsic::x86_sse2_cvttsd2si64:
-      return true;
+  const IntrinsicInfo & IInfo = FR->getIntrinsicInfo();
+  if (IInfo.ID != llvm::Intrinsic::not_intrinsic) {
+    return ( (IInfo.hasAttribute(llvm::Attribute::ReadNone) ||
+              IInfo.hasAttribute(llvm::Attribute::ReadOnly)) &&
+            IInfo.hasAttribute(llvm::Attribute::NoUnwind) );
   }
 
-  // FIXME: Special handling of LLVM IR instructions.
   llvm_unreachable("All cases are covered.");
 }
 
@@ -76,8 +44,7 @@ static bool isInstructionTriviallyDead(SILInstruction *I) {
   if (const ApplyInst *AI = dyn_cast<ApplyInst>(I)) {
     if (BuiltinFunctionRefInst *FR =
         dyn_cast<BuiltinFunctionRefInst>(AI->getCallee().getDef())) {
-      if (isSideEffectFree(FR))
-        return true;
+      return isSideEffectFree(FR);
     }
   }