Do not emit undefined lsrh/ashr for NEON shifts
These IR instructions are undefined when the amount is equal to operand
size, but NEON right shifts support such shifts. Work around that by
emitting a different IR in these cases.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@191953 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGBuiltin.cpp b/lib/CodeGen/CGBuiltin.cpp
index b4caab2..2fe4167 100644
--- a/lib/CodeGen/CGBuiltin.cpp
+++ b/lib/CodeGen/CGBuiltin.cpp
@@ -1657,6 +1657,39 @@
return llvm::ConstantVector::getSplat(VTy->getNumElements(), C);
}
+// \brief Right-shift a vector by a constant.
+Value *CodeGenFunction::EmitNeonRShiftImm(Value *Vec, Value *Shift,
+ llvm::Type *Ty, bool usgn,
+ const char *name) {
+ llvm::VectorType *VTy = cast<llvm::VectorType>(Ty);
+
+ int ShiftAmt = cast<ConstantInt>(Shift)->getSExtValue();
+ int EltSize = VTy->getScalarSizeInBits();
+
+ Vec = Builder.CreateBitCast(Vec, Ty);
+
+ // lshr/ashr are undefined when the shift amount is equal to the vector
+ // element size.
+ if (ShiftAmt == EltSize) {
+ if (usgn) {
+ // Right-shifting an unsigned value by its size yields 0.
+ llvm::Constant *Zero = ConstantInt::get(VTy->getElementType(), 0);
+ return llvm::ConstantVector::getSplat(VTy->getNumElements(), Zero);
+ } else {
+ // Right-shifting a signed value by its size is equivalent
+ // to a shift of size-1.
+ --ShiftAmt;
+ Shift = ConstantInt::get(VTy->getElementType(), ShiftAmt);
+ }
+ }
+
+ Shift = EmitNeonShiftVector(Shift, Ty, false);
+ if (usgn)
+ return Builder.CreateLShr(Vec, Shift, name);
+ else
+ return Builder.CreateAShr(Vec, Shift, name);
+}
+
/// GetPointeeAlignment - Given an expression with a pointer type, find the
/// alignment of the type referenced by the pointer. Skip over implicit
/// casts.
@@ -3125,12 +3158,7 @@
Ops, "vshrn_n", 1, true);
case ARM::BI__builtin_neon_vshr_n_v:
case ARM::BI__builtin_neon_vshrq_n_v:
- Ops[0] = Builder.CreateBitCast(Ops[0], Ty);
- Ops[1] = EmitNeonShiftVector(Ops[1], Ty, false);
- if (usgn)
- return Builder.CreateLShr(Ops[0], Ops[1], "vshr_n");
- else
- return Builder.CreateAShr(Ops[0], Ops[1], "vshr_n");
+ return EmitNeonRShiftImm(Ops[0], Ops[1], Ty, usgn, "vshr_n");
case ARM::BI__builtin_neon_vsri_n_v:
case ARM::BI__builtin_neon_vsriq_n_v:
rightShift = true;
@@ -3142,12 +3170,7 @@
case ARM::BI__builtin_neon_vsra_n_v:
case ARM::BI__builtin_neon_vsraq_n_v:
Ops[0] = Builder.CreateBitCast(Ops[0], Ty);
- Ops[1] = Builder.CreateBitCast(Ops[1], Ty);
- Ops[2] = EmitNeonShiftVector(Ops[2], Ty, false);
- if (usgn)
- Ops[1] = Builder.CreateLShr(Ops[1], Ops[2], "vsra_n");
- else
- Ops[1] = Builder.CreateAShr(Ops[1], Ops[2], "vsra_n");
+ Ops[1] = EmitNeonRShiftImm(Ops[1], Ops[2], Ty, usgn, "vsra_n");
return Builder.CreateAdd(Ops[0], Ops[1]);
case ARM::BI__builtin_neon_vst1_v:
case ARM::BI__builtin_neon_vst1q_v:
diff --git a/lib/CodeGen/CodeGenFunction.h b/lib/CodeGen/CodeGenFunction.h
index 8c506ac..19c64b7 100644
--- a/lib/CodeGen/CodeGenFunction.h
+++ b/lib/CodeGen/CodeGenFunction.h
@@ -2155,6 +2155,8 @@
llvm::Value *EmitNeonSplat(llvm::Value *V, llvm::Constant *Idx);
llvm::Value *EmitNeonShiftVector(llvm::Value *V, llvm::Type *Ty,
bool negateForRightShift);
+ llvm::Value *EmitNeonRShiftImm(llvm::Value *Vec, llvm::Value *Amt,
+ llvm::Type *Ty, bool usgn, const char *name);
llvm::Value *BuildVector(ArrayRef<llvm::Value*> Ops);
llvm::Value *EmitX86BuiltinExpr(unsigned BuiltinID, const CallExpr *E);