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Emit CK_NoOp casts in C mode, not just C++. 

Previously, it had been using CK_BitCast even for casts that only
change const/restrict/volatile. Now it will use CK_Noop where
appropriate.

This is an alternate solution to r336746.

Differential Revision: https://reviews.llvm.org/D52918

llvm-svn: 343892
This commit is contained in:
James Y Knight 2018-10-05 21:53:51 +00:00
parent dc97118efe
commit 49bf370a8b
3 changed files with 34 additions and 6 deletions
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6
clang/lib/AST/ExprConstant.cpp
View File

@ -5864,11 +5864,7 @@ bool PointerExprEvaluator::VisitCastExpr(const CastExpr *E) {
// permitted in constant expressions in C++11. Bitcasts from cv void* are
// also static_casts, but we disallow them as a resolution to DR1312.
if (!E->getType()->isVoidPointerType()) {
// If we changed anything other than cvr-qualifiers, we can't use this
// value for constant folding. FIXME: Qualification conversions should
// always be CK_NoOp, but we get this wrong in C.
if (!Info.Ctx.hasCvrSimilarType(E->getType(), E->getSubExpr()->getType()))
Result.Designator.setInvalid();
Result.Designator.setInvalid();
if (SubExpr->getType()->isVoidPointerType())
CCEDiag(E, diag::note_constexpr_invalid_cast)
<< 3 << SubExpr->getType();

9
clang/lib/Sema/SemaExpr.cpp
View File

@ -5862,6 +5862,8 @@ CastKind Sema::PrepareScalarCast(ExprResult &Src, QualType DestTy) {
LangAS DestAS = DestTy->getPointeeType().getAddressSpace();
if (SrcAS != DestAS)
return CK_AddressSpaceConversion;
if (Context.hasCvrSimilarType(SrcTy, DestTy))
return CK_NoOp;
return CK_BitCast;
}
case Type::STK_BlockPointer:
@ -7762,7 +7764,12 @@ Sema::CheckAssignmentConstraints(QualType LHSType, ExprResult &RHS,
if (isa<PointerType>(RHSType)) {
LangAS AddrSpaceL = LHSPointer->getPointeeType().getAddressSpace();
LangAS AddrSpaceR = RHSType->getPointeeType().getAddressSpace();
Kind = AddrSpaceL != AddrSpaceR ? CK_AddressSpaceConversion : CK_BitCast;
if (AddrSpaceL != AddrSpaceR)
Kind = CK_AddressSpaceConversion;
else if (Context.hasCvrSimilarType(RHSType, LHSType))
Kind = CK_NoOp;
else
Kind = CK_BitCast;
return checkPointerTypesForAssignment(*this, LHSType, RHSType);
}

25
clang/test/Sema/c-casts.c Normal file
View File

@ -0,0 +1,25 @@
// RUN: %clang_cc1 -w -ast-dump %s | FileCheck %s
// The cast construction code both for implicit and c-style casts is very
// different in C vs C++. This file is intended to test the C behavior.
// TODO: add tests covering the rest of the code in
// Sema::CheckAssignmentConstraints and Sema::PrepareScalarCast
// CHECK-LABEL: FunctionDecl {{.*}} cast_cvr_pointer
void cast_cvr_pointer(char volatile * __restrict * const * p) {
char*** x;
// CHECK: ImplicitCastExpr {{.*}} 'char ***' <NoOp>
x = p;
// CHECK: CStyleCastExpr {{.*}} 'char ***' <NoOp>
x = (char***)p;
}
// CHECK-LABEL: FunctionDecl {{.*}} cast_pointer_type
void cast_pointer_type(char *p) {
void *x;
// CHECK: ImplicitCastExpr {{.*}} 'void *' <BitCast>
x = p;
// CHECK: CStyleCastExpr {{.*}} 'void *' <BitCast>
x = (void*)p;
}