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!

llvm-svn: 146357

1 files changed, 8 insertions, 4 deletions

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 7e98b21..8e2f263 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/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());
         }
       }