clang: Remove upstream diff in read_exec builtins (llvm#804)

Author: ronlieb

clang/lib/CodeGen/CGBuiltin.cpp

@@ -8989,27 +8989,24 @@ enum SpecialRegisterAccessKind {
   Write,
 };
 
+// Generates the IR for __builtin_read_exec_*.
+// Lowers the builtin to amdgcn_ballot intrinsic.
 static Value *EmitAMDGCNBallotForExec(CodeGenFunction &CGF, const CallExpr *E,
                                       llvm::Type *RegisterType,
                                       llvm::Type *ValueType, bool isExecHi) {
   CodeGen::CGBuilderTy &Builder = CGF.Builder;
   CodeGen::CodeGenModule &CGM = CGF.CGM;
 
-  llvm::Type *ResultType = CGF.ConvertType(E->getType());
-  llvm::Value *Call;
-  Function *F;
+  Function *F = CGM.getIntrinsic(Intrinsic::amdgcn_ballot, {RegisterType});
+  llvm::Value *Call = Builder.CreateCall(F, {Builder.getInt1(true)});
+
   if (isExecHi) {
-    F = CGM.getIntrinsic(Intrinsic::amdgcn_ballot, {RegisterType});
-    Call = Builder.CreateCall(F, {Builder.getInt1(true)});
-    Value *C1 = llvm::ConstantInt::get(ValueType, 32);
-    Value *Rt2 = Builder.CreateLShr(Call, C1);
-    Value *Rt3 = Builder.CreateTruncOrBitCast(Rt2, CGF.Int32Ty);
-    return Rt3;
-  } else {
-    F = CGM.getIntrinsic(Intrinsic::amdgcn_ballot, {ResultType});
-    Call = Builder.CreateCall(F, {Builder.getInt1(true)});
-    return Call;
+    Value *Rt2 = Builder.CreateLShr(Call, 32);
+    Rt2 = Builder.CreateTrunc(Rt2, CGF.Int32Ty);
+    return Rt2;
   }
+
+  return Call;
 }
 
 // Generates the IR for the read/write special register builtin,