Switch llvm.cttz and llvm.ctlz to accept a second i1 parameter which

indicates whether the intrinsic has a defined result for a first
argument equal to zero. This will eventually allow these intrinsics to
accurately model the semantics of GCC's __builtin_ctz and __builtin_clz
and the X86 instructions (prior to AVX) which implement them.

This patch merely sets the stage by extending the signature of these
intrinsics and establishing auto-upgrade logic so that the old spelling
still works both in IR and in bitcode. The upgrade logic preserves the
existing (inefficient) semantics. This patch should not change any
behavior. CodeGen isn't updated because it can use the existing
semantics regardless of the flag's value.

Note that this will be followed by API updates to Clang and DragonEgg.

Reviewed by Nick Lewycky!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146357 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 42 insertions, 11 deletions

diff --git a/lib/Analysis/ConstantFolding.cpp b/lib/Analysis/ConstantFolding.cpp
index 7e98b21888..8e2f263cd4 100644
--- a/lib/Analysis/ConstantFolding.cpp
+++ b/lib/Analysis/ConstantFolding.cpp
@@ -1290,10 +1290,6 @@ llvm::ConstantFoldCall(Function *F, ArrayRef<Constant *> Operands,
         return ConstantInt::get(F->getContext(), Op->getValue().byteSwap());
       case Intrinsic::ctpop:
         return ConstantInt::get(Ty, Op->getValue().countPopulation());
-      case Intrinsic::cttz:
-        return ConstantInt::get(Ty, Op->getValue().countTrailingZeros());
-      case Intrinsic::ctlz:
-        return ConstantInt::get(Ty, Op->getValue().countLeadingZeros());
       case Intrinsic::convert_from_fp16: {
         APFloat Val(Op->getValue());
 
@@ -1418,6 +1414,14 @@ llvm::ConstantFoldCall(Function *F, ArrayRef<Constant *> Operands,
           };
           return ConstantStruct::get(cast<StructType>(F->getReturnType()), Ops);
         }
+        case Intrinsic::cttz:
+          // FIXME: This should check for Op2 == 1, and become unreachable if
+          // Op1 == 0.
+          return ConstantInt::get(Ty, Op1->getValue().countTrailingZeros());
+        case Intrinsic::ctlz:
+          // FIXME: This should check for Op2 == 1, and become unreachable if
+          // Op1 == 0.
+          return ConstantInt::get(Ty, Op1->getValue().countLeadingZeros());
         }
       }
       
diff --git a/lib/Transforms/Scalar/SimplifyLibCalls.cpp b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
index 6e169de829..075adc0187 100644
--- a/lib/Transforms/Scalar/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
@@ -999,7 +999,7 @@ struct FFSOpt : public LibCallOptimization {
     Type *ArgType = Op->getType();
     Value *F = Intrinsic::getDeclaration(Callee->getParent(),
                                          Intrinsic::cttz, ArgType);
-    Value *V = B.CreateCall(F, Op, "cttz");
+    Value *V = B.CreateCall2(F, Op, B.getFalse(), "cttz");
     V = B.CreateAdd(V, ConstantInt::get(V->getType(), 1));
     V = B.CreateIntCast(V, B.getInt32Ty(), false);
 
diff --git a/lib/VMCore/AutoUpgrade.cpp b/lib/VMCore/AutoUpgrade.cpp
index 373524cdf3..6bdb115a9a 100644
--- a/lib/VMCore/AutoUpgrade.cpp
+++ b/lib/VMCore/AutoUpgrade.cpp
@@ -40,7 +40,20 @@ static bool UpgradeIntrinsicFunction1(Function *F, Function *&NewFn) {
 
   switch (Name[0]) {
   default: break;
-  // SOMEDAY: Add some.
+  case 'c': {
+    Type *Tys[] = { F->arg_begin()->getType() };
+    if (Name.startswith("ctlz.") && F->arg_size() == 1) {
+      F->setName(Name + ".old");
+      NewFn = Intrinsic::getDeclaration(F->getParent(), Intrinsic::ctlz, Tys);
+      return true;
+    }
+    if (Name.startswith("cttz.") && F->arg_size() == 1) {
+      F->setName(Name + ".old");
+      NewFn = Intrinsic::getDeclaration(F->getParent(), Intrinsic::cttz, Tys);
+      return true;
+    }
+    break;
+  }
   }
 
   //  This may not belong here. This function is effectively being overloaded 
@@ -72,15 +85,29 @@ bool llvm::UpgradeGlobalVariable(GlobalVariable *GV) {
 // order to seamlessly integrate with existing context.
 void llvm::UpgradeIntrinsicCall(CallInst *CI, Function *NewFn) {
   Function *F = CI->getCalledFunction();
+  LLVMContext &C = CI->getContext();
 
   assert(F && "CallInst has no function associated with it.");
 
-  if (NewFn) return;
-  
-  if (F->getName() == "llvm.something eventually") {
-    // UPGRADE HERE.
-  } else {
+  if (!NewFn) return;
+
+  IRBuilder<> Builder(C);
+  Builder.SetInsertPoint(CI->getParent(), CI);
+
+  switch (NewFn->getIntrinsicID()) {
+  default:
     llvm_unreachable("Unknown function for CallInst upgrade.");
+
+  case Intrinsic::ctlz:
+  case Intrinsic::cttz:
+    assert(CI->getNumArgOperands() == 1 &&
+           "Mismatch between function args and call args");
+    StringRef Name = CI->getName();
+    CI->setName(Name + ".old");
+    CI->replaceAllUsesWith(Builder.CreateCall2(NewFn, CI->getArgOperand(0),
+                                               Builder.getFalse(), Name));
+    CI->eraseFromParent();
+    return;
   }
 }