P0145R3 (C++17 evaluation order tweaks): consistently emit the LHS of array
subscripting before the RHS, regardless of which is the base and which is the
index.
llvm-svn: 282453
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 7fee798..c6011cb 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -2875,13 +2875,30 @@
LValue CodeGenFunction::EmitArraySubscriptExpr(const ArraySubscriptExpr *E,
bool Accessed) {
- // The index must always be an integer, which is not an aggregate. Emit it.
- llvm::Value *Idx = EmitScalarExpr(E->getIdx());
- QualType IdxTy = E->getIdx()->getType();
- bool IdxSigned = IdxTy->isSignedIntegerOrEnumerationType();
+ // The index must always be an integer, which is not an aggregate. Emit it
+ // in lexical order (this complexity is, sadly, required by C++17).
+ llvm::Value *IdxPre =
+ (E->getLHS() == E->getIdx()) ? EmitScalarExpr(E->getIdx()) : nullptr;
+ auto EmitIdxAfterBase = [&, IdxPre](bool Promote = true) -> llvm::Value * {
+ auto *Idx = IdxPre;
+ if (E->getLHS() != E->getIdx()) {
+ assert(E->getRHS() == E->getIdx() && "index was neither LHS nor RHS");
+ Idx = EmitScalarExpr(E->getIdx());
+ }
- if (SanOpts.has(SanitizerKind::ArrayBounds))
- EmitBoundsCheck(E, E->getBase(), Idx, IdxTy, Accessed);
+ QualType IdxTy = E->getIdx()->getType();
+ bool IdxSigned = IdxTy->isSignedIntegerOrEnumerationType();
+
+ if (SanOpts.has(SanitizerKind::ArrayBounds))
+ EmitBoundsCheck(E, E->getBase(), Idx, IdxTy, Accessed);
+
+ // Extend or truncate the index type to 32 or 64-bits.
+ if (Promote && Idx->getType() != IntPtrTy)
+ Idx = Builder.CreateIntCast(Idx, IntPtrTy, IdxSigned, "idxprom");
+
+ return Idx;
+ };
+ IdxPre = nullptr;
// If the base is a vector type, then we are forming a vector element lvalue
// with this subscript.
@@ -2889,6 +2906,7 @@
!isa<ExtVectorElementExpr>(E->getBase())) {
// Emit the vector as an lvalue to get its address.
LValue LHS = EmitLValue(E->getBase());
+ auto *Idx = EmitIdxAfterBase(/*Promote*/false);
assert(LHS.isSimple() && "Can only subscript lvalue vectors here!");
return LValue::MakeVectorElt(LHS.getAddress(), Idx,
E->getBase()->getType(),
@@ -2897,13 +2915,10 @@
// All the other cases basically behave like simple offsetting.
- // Extend or truncate the index type to 32 or 64-bits.
- if (Idx->getType() != IntPtrTy)
- Idx = Builder.CreateIntCast(Idx, IntPtrTy, IdxSigned, "idxprom");
-
// Handle the extvector case we ignored above.
if (isa<ExtVectorElementExpr>(E->getBase())) {
LValue LV = EmitLValue(E->getBase());
+ auto *Idx = EmitIdxAfterBase(/*Promote*/true);
Address Addr = EmitExtVectorElementLValue(LV);
QualType EltType = LV.getType()->castAs<VectorType>()->getElementType();
@@ -2919,6 +2934,7 @@
// it. It needs to be emitted first in case it's what captures
// the VLA bounds.
Addr = EmitPointerWithAlignment(E->getBase(), &AlignSource);
+ auto *Idx = EmitIdxAfterBase(/*Promote*/true);
// The element count here is the total number of non-VLA elements.
llvm::Value *numElements = getVLASize(vla).first;
@@ -2938,14 +2954,16 @@
} else if (const ObjCObjectType *OIT = E->getType()->getAs<ObjCObjectType>()){
// Indexing over an interface, as in "NSString *P; P[4];"
- CharUnits InterfaceSize = getContext().getTypeSizeInChars(OIT);
- llvm::Value *InterfaceSizeVal =
- llvm::ConstantInt::get(Idx->getType(), InterfaceSize.getQuantity());;
-
- llvm::Value *ScaledIdx = Builder.CreateMul(Idx, InterfaceSizeVal);
// Emit the base pointer.
Addr = EmitPointerWithAlignment(E->getBase(), &AlignSource);
+ auto *Idx = EmitIdxAfterBase(/*Promote*/true);
+
+ CharUnits InterfaceSize = getContext().getTypeSizeInChars(OIT);
+ llvm::Value *InterfaceSizeVal =
+ llvm::ConstantInt::get(Idx->getType(), InterfaceSize.getQuantity());
+
+ llvm::Value *ScaledIdx = Builder.CreateMul(Idx, InterfaceSizeVal);
// We don't necessarily build correct LLVM struct types for ObjC
// interfaces, so we can't rely on GEP to do this scaling
@@ -2977,6 +2995,7 @@
ArrayLV = EmitArraySubscriptExpr(ASE, /*Accessed*/ true);
else
ArrayLV = EmitLValue(Array);
+ auto *Idx = EmitIdxAfterBase(/*Promote*/true);
// Propagate the alignment from the array itself to the result.
Addr = emitArraySubscriptGEP(*this, ArrayLV.getAddress(),
@@ -2987,6 +3006,7 @@
} else {
// The base must be a pointer; emit it with an estimate of its alignment.
Addr = EmitPointerWithAlignment(E->getBase(), &AlignSource);
+ auto *Idx = EmitIdxAfterBase(/*Promote*/true);
Addr = emitArraySubscriptGEP(*this, Addr, Idx, E->getType(),
!getLangOpts().isSignedOverflowDefined());
}