[CodeGen] add/fix rotate builtins that map to LLVM funnel shift (retry)

This is a retry of rL340135 (reverted at rL340136 because of gcc host compiler crashing)
with 2 changes:
1. Move the code into a helper to reduce code duplication (and hopefully work-around the crash).
2. The original commit had a formatting bug in the docs (missing an underscore).

Original commit message:

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:
https://reviews.llvm.org/D49242

With improved codegen in:
https://reviews.llvm.org/rL337966
https://reviews.llvm.org/rL339359

And basic IR optimization added in:
https://reviews.llvm.org/rL338218
https://reviews.llvm.org/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: 340137

clang/docs/LanguageExtensions.rst

@@ -1739,6 +1739,70 @@ The '``__builtin_bitreverse``' family of builtins is used to reverse
 the bitpattern of an integer value; for example ``0b10110110`` becomes
 ``0b01101101``.
 
+``__builtin_rotateleft``
+------------------------
+
+* ``__builtin_rotateleft8``
+* ``__builtin_rotateleft16``
+* ``__builtin_rotateleft32``
+* ``__builtin_rotateleft64``
+
+**Syntax**:
+
+.. code-block:: c++
+
+     __builtin_rotateleft32(x, y)
+
+**Examples**:
+
+.. code-block:: c++
+
+      uint8_t rot_x = __builtin_rotateleft8(x, y);
+      uint16_t rot_x = __builtin_rotateleft16(x, y);
+      uint32_t rot_x = __builtin_rotateleft32(x, y);
+      uint64_t rot_x = __builtin_rotateleft64(x, y);
+
+**Description**:
+
+The '``__builtin_rotateleft``' family of builtins is used to rotate
+the bits in the first argument by the amount in the second argument. 
+For example, ``0b10000110`` rotated left by 11 becomes ``0b00110100``.
+The shift value is treated as an unsigned amount modulo the size of
+the arguments. Both arguments and the result have the bitwidth specified
+by the name of the builtin.
+
+``__builtin_rotateright``
+_------------------------
+
+* ``__builtin_rotateright8``
+* ``__builtin_rotateright16``
+* ``__builtin_rotateright32``
+* ``__builtin_rotateright64``
+
+**Syntax**:
+
+.. code-block:: c++
+
+     __builtin_rotateright32(x, y)
+
+**Examples**:
+
+.. code-block:: c++
+
+      uint8_t rot_x = __builtin_rotateright8(x, y);
+      uint16_t rot_x = __builtin_rotateright16(x, y);
+      uint32_t rot_x = __builtin_rotateright32(x, y);
+      uint64_t rot_x = __builtin_rotateright64(x, y);
+
+**Description**:
+
+The '``__builtin_rotateright``' family of builtins is used to rotate
+the bits in the first argument by the amount in the second argument. 
+For example, ``0b10000110`` rotated right by 3 becomes ``0b11010000``.
+The shift value is treated as an unsigned amount modulo the size of
+the arguments. Both arguments and the result have the bitwidth specified
+by the name of the builtin.
+
 ``__builtin_unreachable``
 -------------------------
 

clang/include/clang/Basic/Builtins.def

@@ -428,6 +428,15 @@ BUILTIN(__builtin_bitreverse16, "UsUs", "nc")
 BUILTIN(__builtin_bitreverse32, "UiUi", "nc")
 BUILTIN(__builtin_bitreverse64, "ULLiULLi", "nc")
 
+BUILTIN(__builtin_rotateleft8, "UcUcUc", "nc")
+BUILTIN(__builtin_rotateleft16, "UsUsUs", "nc")
+BUILTIN(__builtin_rotateleft32, "UiUiUi", "nc")
+BUILTIN(__builtin_rotateleft64, "ULLiULLiULLi", "nc")
+BUILTIN(__builtin_rotateright8, "UcUcUc", "nc")
+BUILTIN(__builtin_rotateright16, "UsUsUs", "nc")
+BUILTIN(__builtin_rotateright32, "UiUiUi", "nc")
+BUILTIN(__builtin_rotateright64, "ULLiULLiULLi", "nc")
+
 // Random GCC builtins
 BUILTIN(__builtin_constant_p, "i.", "nctu")
 BUILTIN(__builtin_classify_type, "i.", "nctu")

clang/lib/CodeGen/CGBuiltin.cpp

@@ -1252,6 +1252,21 @@ static llvm::Value *dumpRecord(CodeGenFunction &CGF, QualType RType,
   return Res;
 }
 
+RValue CodeGenFunction::emitRotate(const CallExpr *E, bool IsRotateRight) {
+  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);
+
+  // Rotate is a special case of LLVM funnel shift - 1st 2 args are the same.
+  unsigned IID = IsRotateRight ? Intrinsic::fshr : Intrinsic::fshl;
+  Value *F = CGM.getIntrinsic(IID, Ty);
+  return RValue::get(Builder.CreateCall(F, { Src, Src, ShiftAmt }));
+}
+
 RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
                                         unsigned BuiltinID, const CallExpr *E,
                                         ReturnValueSlot ReturnValue) {
@@ -1647,46 +1662,6 @@ 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 +1716,28 @@ 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:
+    return emitRotate(E, false);
+
+  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:
+    return emitRotate(E, true);
+
   case Builtin::BI__builtin_object_size: {
     unsigned Type =
         E->getArg(1)->EvaluateKnownConstInt(getContext()).getZExtValue();

clang/lib/CodeGen/CodeGenFunction.h

@@ -3681,6 +3681,8 @@ class CodeGenFunction : public CodeGenTypeCache {
                          unsigned BuiltinID, const CallExpr *E,
                          ReturnValueSlot ReturnValue);
 
+  RValue emitRotate(const CallExpr *E, bool IsRotateRight);
+
   /// Emit IR for __builtin_os_log_format.
   RValue emitBuiltinOSLogFormat(const CallExpr &E);
 

clang/test/CodeGen/builtin-rotate.c

@@ -0,0 +1,66 @@
+// RUN: %clang_cc1 %s -emit-llvm -o - | FileCheck %s
+
+unsigned char rotl8(unsigned char x, unsigned char y) {
+// CHECK-LABEL: rotl8
+// CHECK: [[F:%.*]] = call i8 @llvm.fshl.i8(i8 [[X:%.*]], i8 [[X]], i8 [[Y:%.*]])
+// CHECK-NEXT: ret i8 [[F]]
+
+  return __builtin_rotateleft8(x, y);
+}
+
+short rotl16(short x, short y) {
+// CHECK-LABEL: rotl16
+// CHECK: [[F:%.*]] = call i16 @llvm.fshl.i16(i16 [[X:%.*]], i16 [[X]], i16 [[Y:%.*]])
+// CHECK-NEXT: ret i16 [[F]]
+
+  return __builtin_rotateleft16(x, y);
+}
+
+int rotl32(int x, unsigned int y) {
+// CHECK-LABEL: rotl32
+// CHECK: [[F:%.*]] = call i32 @llvm.fshl.i32(i32 [[X:%.*]], i32 [[X]], i32 [[Y:%.*]])
+// CHECK-NEXT: ret i32 [[F]]
+
+  return __builtin_rotateleft32(x, y);
+}
+
+unsigned long long rotl64(unsigned long long x, long long y) {
+// CHECK-LABEL: rotl64
+// CHECK: [[F:%.*]] = call i64 @llvm.fshl.i64(i64 [[X:%.*]], i64 [[X]], i64 [[Y:%.*]])
+// CHECK-NEXT: ret i64 [[F]]
+
+  return __builtin_rotateleft64(x, y);
+}
+
+char rotr8(char x, char y) {
+// CHECK-LABEL: rotr8
+// CHECK: [[F:%.*]] = call i8 @llvm.fshr.i8(i8 [[X:%.*]], i8 [[X]], i8 [[Y:%.*]])
+// CHECK-NEXT: ret i8 [[F]]
+
+  return __builtin_rotateright8(x, y);
+}
+
+unsigned short rotr16(unsigned short x, unsigned short y) {
+// CHECK-LABEL: rotr16
+// CHECK: [[F:%.*]] = call i16 @llvm.fshr.i16(i16 [[X:%.*]], i16 [[X]], i16 [[Y:%.*]])
+// CHECK-NEXT: ret i16 [[F]]
+
+  return __builtin_rotateright16(x, y);
+}
+
+unsigned int rotr32(unsigned int x, int y) {
+// CHECK-LABEL: rotr32
+// CHECK: [[F:%.*]] = call i32 @llvm.fshr.i32(i32 [[X:%.*]], i32 [[X]], i32 [[Y:%.*]])
+// CHECK-NEXT: ret i32 [[F]]
+
+  return __builtin_rotateright32(x, y);
+}
+
+long long rotr64(long long x, unsigned long long y) {
+// CHECK-LABEL: rotr64
+// CHECK: [[F:%.*]] = call i64 @llvm.fshr.i64(i64 [[X:%.*]], i64 [[X]], i64 [[Y:%.*]])
+// CHECK-NEXT: ret i64 [[F]]
+
+  return __builtin_rotateright64(x, y);
+}
+