[CodeGen] add rotate builtins

This exposes the LLVM funnel shift intrinsics as more familiar bit rotation functions in clang 
(when both halves of a funnel shift are the same value, it's a rotate).

We're free to name these as we want because we're not copying gcc, but if there's some other 
existing art (eg, the microsoft ops that are modified in this patch) that we want to replicate, 
we can change the names.

The funnel shift intrinsics were added here:
D49242

With improved codegen in:
rL337966
rL339359

And basic IR optimization added in:
rL338218
rL340022

...so these are expected to produce asm output that's equal or better to the multi-instruction 
alternatives using primitive C/IR ops.

In the motivating loop example from PR37387:
https://bugs.llvm.org/show_bug.cgi?id=37387#c7
...we get the expected 'rolq' x86 instructions if we substitute the rotate builtin into the source.

Differential Revision: https://reviews.llvm.org/D50924

llvm-svn: 340135

1 files changed, 37 insertions, 40 deletions

diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index 5b8a272d589..abcd1d45969 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -1647,46 +1647,6 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
                                      "cast");
     return RValue::get(Result);
   }
-  case Builtin::BI_rotr8:
-  case Builtin::BI_rotr16:
-  case Builtin::BI_rotr:
-  case Builtin::BI_lrotr:
-  case Builtin::BI_rotr64: {
-    Value *Val = EmitScalarExpr(E->getArg(0));
-    Value *Shift = EmitScalarExpr(E->getArg(1));
-
-    llvm::Type *ArgType = Val->getType();
-    Shift = Builder.CreateIntCast(Shift, ArgType, false);
-    unsigned ArgWidth = ArgType->getIntegerBitWidth();
-    Value *Mask = llvm::ConstantInt::get(ArgType, ArgWidth - 1);
-
-    Value *RightShiftAmt = Builder.CreateAnd(Shift, Mask);
-    Value *RightShifted = Builder.CreateLShr(Val, RightShiftAmt);
-    Value *LeftShiftAmt = Builder.CreateAnd(Builder.CreateNeg(Shift), Mask);
-    Value *LeftShifted = Builder.CreateShl(Val, LeftShiftAmt);
-    Value *Result = Builder.CreateOr(LeftShifted, RightShifted);
-    return RValue::get(Result);
-  }
-  case Builtin::BI_rotl8:
-  case Builtin::BI_rotl16:
-  case Builtin::BI_rotl:
-  case Builtin::BI_lrotl:
-  case Builtin::BI_rotl64: {
-    Value *Val = EmitScalarExpr(E->getArg(0));
-    Value *Shift = EmitScalarExpr(E->getArg(1));
-
-    llvm::Type *ArgType = Val->getType();
-    Shift = Builder.CreateIntCast(Shift, ArgType, false);
-    unsigned ArgWidth = ArgType->getIntegerBitWidth();
-    Value *Mask = llvm::ConstantInt::get(ArgType, ArgWidth - 1);
-
-    Value *LeftShiftAmt = Builder.CreateAnd(Shift, Mask);
-    Value *LeftShifted = Builder.CreateShl(Val, LeftShiftAmt);
-    Value *RightShiftAmt = Builder.CreateAnd(Builder.CreateNeg(Shift), Mask);
-    Value *RightShifted = Builder.CreateLShr(Val, RightShiftAmt);
-    Value *Result = Builder.CreateOr(LeftShifted, RightShifted);
-    return RValue::get(Result);
-  }
   case Builtin::BI__builtin_unpredictable: {
     // Always return the argument of __builtin_unpredictable. LLVM does not
     // handle this builtin. Metadata for this builtin should be added directly
@@ -1741,6 +1701,43 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
   case Builtin::BI__builtin_bitreverse64: {
     return RValue::get(emitUnaryBuiltin(*this, E, Intrinsic::bitreverse));
   }
+  case Builtin::BI__builtin_rotateleft8:
+  case Builtin::BI__builtin_rotateleft16:
+  case Builtin::BI__builtin_rotateleft32:
+  case Builtin::BI__builtin_rotateleft64:
+  case Builtin::BI_rotl8: // Microsoft variants of rotate left
+  case Builtin::BI_rotl16:
+  case Builtin::BI_rotl:
+  case Builtin::BI_lrotl:
+  case Builtin::BI_rotl64: {
+    llvm::Value *Src = EmitScalarExpr(E->getArg(0));
+    llvm::Value *ShiftAmt = EmitScalarExpr(E->getArg(1));
+    // The builtin's shift arg may have a different type than the source arg and
+    // result, but the LLVM intrinsic uses the same type for all values.
+    llvm::Type *Ty = Src->getType();
+    ShiftAmt = Builder.CreateIntCast(ShiftAmt, Ty, false);
+    Value *F = CGM.getIntrinsic(Intrinsic::fshl, Ty);
+    return RValue::get(Builder.CreateCall(F, { Src, Src, ShiftAmt }));
+  }
+  case Builtin::BI__builtin_rotateright8:
+  case Builtin::BI__builtin_rotateright16:
+  case Builtin::BI__builtin_rotateright32:
+  case Builtin::BI__builtin_rotateright64:
+  case Builtin::BI_rotr8: // Microsoft variants of rotate right
+  case Builtin::BI_rotr16:
+  case Builtin::BI_rotr:
+  case Builtin::BI_lrotr:
+  case Builtin::BI_rotr64: {
+    llvm::Value *Src = EmitScalarExpr(E->getArg(0));
+    llvm::Value *ShiftAmt = EmitScalarExpr(E->getArg(1));
+    // The builtin's shift arg may have a different type than the source arg and
+    // result, but the LLVM intrinsic uses the same type for all values.
+    llvm::Type *Ty = Src->getType();
+    ShiftAmt = Builder.CreateIntCast(ShiftAmt, Ty, false);
+    Value *F = CGM.getIntrinsic(Intrinsic::fshr, Ty);
+    return RValue::get(Builder.CreateCall(F, { Src, Src, ShiftAmt }));
+  }
+
   case Builtin::BI__builtin_object_size: {
     unsigned Type =
         E->getArg(1)->EvaluateKnownConstInt(getContext()).getZExtValue();