Fix redundant load of bit-fields on assignment (to get the updated
value).
- Use extra argument to EmitStoreThroughLValue to provide place to
write update bit-field value if caller requires it.
- This fixes several FIXMEs.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59615 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGExpr.cpp b/lib/CodeGen/CGExpr.cpp
index 95733ab..9328a53 100644
--- a/lib/CodeGen/CGExpr.cpp
+++ b/lib/CodeGen/CGExpr.cpp
@@ -392,7 +392,8 @@
}
void CodeGenFunction::EmitStoreThroughBitfieldLValue(RValue Src, LValue Dst,
- QualType Ty) {
+ QualType Ty,
+ llvm::Value **Result) {
unsigned StartBit = Dst.getBitfieldStartBit();
unsigned BitfieldSize = Dst.getBitfieldSize();
llvm::Value *Ptr = Dst.getBitfieldAddr();
@@ -403,12 +404,31 @@
// Get the new value, cast to the appropriate type and masked to
// exactly the size of the bit-field.
- llvm::Value *NewVal = Src.getScalarVal();
- NewVal = Builder.CreateIntCast(NewVal, EltTy, false, "tmp");
+ llvm::Value *SrcVal = Src.getScalarVal();
+ llvm::Value *NewVal = Builder.CreateIntCast(SrcVal, EltTy, false, "tmp");
llvm::Constant *Mask =
llvm::ConstantInt::get(llvm::APInt::getLowBitsSet(EltTySize, BitfieldSize));
NewVal = Builder.CreateAnd(NewVal, Mask, "bf.value");
+ // Return the new value of the bit-field, if requested.
+ if (Result) {
+ // Cast back to the proper type for result.
+ const llvm::Type *SrcTy = SrcVal->getType();
+ llvm::Value *SrcTrunc = Builder.CreateIntCast(NewVal, SrcTy, false,
+ "bf.reload.val");
+
+ // Sign extend if necessary.
+ if (Dst.isBitfieldSigned()) {
+ unsigned SrcTySize = CGM.getTargetData().getTypeSizeInBits(SrcTy);
+ llvm::Value *ExtraBits = llvm::ConstantInt::get(SrcTy,
+ SrcTySize - BitfieldSize);
+ SrcTrunc = Builder.CreateAShr(Builder.CreateShl(SrcTrunc, ExtraBits),
+ ExtraBits, "bf.reload.sext");
+ }
+
+ *Result = SrcTrunc;
+ }
+
// In some cases the bitfield may straddle two memory locations.
// Emit the low part first and check to see if the high needs to be
// done.
diff --git a/lib/CodeGen/CGExprScalar.cpp b/lib/CodeGen/CGExprScalar.cpp
index d87edc3..b236a6a 100644
--- a/lib/CodeGen/CGExprScalar.cpp
+++ b/lib/CodeGen/CGExprScalar.cpp
@@ -786,15 +786,14 @@
// Convert the result back to the LHS type.
Result = EmitScalarConversion(Result, ResultTy, LHSTy);
- // Store the result value into the LHS lvalue.
- CGF.EmitStoreThroughLValue(RValue::get(Result), LHSLV, LHSTy);
-
- // For bitfields, we need the value in the bitfield. Note that
- // property references do not reload their value (even though the
- // setter may have changed it).
- // FIXME: This adds an extra bitfield load
+ // Store the result value into the LHS lvalue. Bit-fields are
+ // handled specially because the result is altered by the store.
if (LHSLV.isBitfield())
- Result = EmitLoadOfLValue(LHSLV, LHSTy);
+ CGF.EmitStoreThroughBitfieldLValue(RValue::get(Result), LHSLV, LHSTy,
+ &Result);
+ else
+ CGF.EmitStoreThroughLValue(RValue::get(Result), LHSLV, LHSTy);
+
return Result;
}
@@ -1003,16 +1002,14 @@
LValue LHS = EmitLValue(E->getLHS());
Value *RHS = Visit(E->getRHS());
- // Store the value into the LHS.
+ // Store the value into the LHS. Bit-fields are handled specially
+ // because the result is altered by the store.
// FIXME: Volatility!
- CGF.EmitStoreThroughLValue(RValue::get(RHS), LHS, E->getType());
-
- // For bitfields, we need the value in the bitfield. Note that
- // property references do not reload their value (even though the
- // setter may have changed it).
- // FIXME: This adds an extra bitfield load
if (LHS.isBitfield())
- return EmitLoadOfLValue(LHS, E->getLHS()->getType());
+ CGF.EmitStoreThroughBitfieldLValue(RValue::get(RHS), LHS, E->getType(),
+ &RHS);
+ else
+ CGF.EmitStoreThroughLValue(RValue::get(RHS), LHS, E->getType());
// Return the RHS.
return RHS;
diff --git a/lib/CodeGen/CodeGenFunction.h b/lib/CodeGen/CodeGenFunction.h
index 5d99dba..05b2793 100644
--- a/lib/CodeGen/CodeGenFunction.h
+++ b/lib/CodeGen/CodeGenFunction.h
@@ -32,6 +32,7 @@
class BasicBlock;
class Module;
class SwitchInst;
+ class Value;
}
namespace clang {
@@ -446,8 +447,16 @@
void EmitStoreThroughLValue(RValue Src, LValue Dst, QualType Ty);
void EmitStoreThroughExtVectorComponentLValue(RValue Src, LValue Dst,
QualType Ty);
- void EmitStoreThroughBitfieldLValue(RValue Src, LValue Dst, QualType Ty);
void EmitStoreThroughPropertyRefLValue(RValue Src, LValue Dst, QualType Ty);
+
+ /// EmitStoreThroughLValue - Store Src into Dst with same
+ /// constraints as EmitStoreThroughLValue.
+ ///
+ /// \param Result [out] - If non-null, this will be set to a Value*
+ /// for the bit-field contents after the store, appropriate for use
+ /// as the result of an assignment to the bit-field.
+ void EmitStoreThroughBitfieldLValue(RValue Src, LValue Dst, QualType Ty,
+ llvm::Value **Result=0);
// Note: only availabe for agg return types
LValue EmitBinaryOperatorLValue(const BinaryOperator *E);
diff --git a/lib/CodeGen/README.txt b/lib/CodeGen/README.txt
index 33fbfdb..12a08e1 100644
--- a/lib/CodeGen/README.txt
+++ b/lib/CodeGen/README.txt
@@ -17,8 +17,3 @@
directly.
//===---------------------------------------------------------------------===//
-
-Bitfields should not reload the stored value just to return the
-correct result.
-
-//===---------------------------------------------------------------------===//