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Document a bug in loop-convert and fix one of its subcases. 

Summary: Now that we prioritize copying trivial types over using const-references where possible, I found some cases where, after the transformation, the loop was using the address of the local copy instead of the original object.

Reviewers: klimek

Subscribers: alexfh, cfe-commits

Differential Revision: http://reviews.llvm.org/D13431

llvm-svn: 249300
This commit is contained in:
Angel Garcia Gomez 2015-10-05 11:15:39 +00:00
parent 72207b167c
commit 199e5232b3
2 changed files with 26 additions and 3 deletions
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17
clang-tools-extra/clang-tidy/modernize/LoopConvertCheck.cpp
View File

@ -477,6 +477,7 @@ void LoopConvertCheck::doConversion(
std::string VarName; std::string VarName;
bool VarNameFromAlias = (Usages.size() == 1) && AliasDecl; bool VarNameFromAlias = (Usages.size() == 1) && AliasDecl;
bool AliasVarIsRef = false; bool AliasVarIsRef = false;
bool CanCopy = true;
if (VarNameFromAlias) { if (VarNameFromAlias) {
const auto *AliasVar = cast<VarDecl>(AliasDecl->getSingleDecl()); const auto *AliasVar = cast<VarDecl>(AliasDecl->getSingleDecl());
@ -525,6 +526,16 @@ void LoopConvertCheck::doConversion(
// and parenthesis around a simple DeclRefExpr can always be // and parenthesis around a simple DeclRefExpr can always be
// removed. // removed.
Range = Paren->getSourceRange(); Range = Paren->getSourceRange();
} else if (const auto *UOP = Parents[0].get<UnaryOperator>()) {
// If we are taking the address of the loop variable, then we must
// not use a copy, as it would mean taking the address of the loop's
// local index instead.
// FIXME: This won't catch cases where the address is taken outside
// of the loop's body (for instance, in a function that got the
// loop's index as a const reference parameter), or where we take
// the address of a member (like "&Arr[i].A.B.C").
if (UOP->getOpcode() == UO_AddrOf)
CanCopy = false;
} }
} }
} else { } else {
@ -548,8 +559,10 @@ void LoopConvertCheck::doConversion(
// If the new variable name is from the aliased variable, then the reference // If the new variable name is from the aliased variable, then the reference
// type for the new variable should only be used if the aliased variable was // type for the new variable should only be used if the aliased variable was
// declared as a reference. // declared as a reference.
bool UseCopy = (VarNameFromAlias && !AliasVarIsRef) || bool UseCopy =
(Descriptor.DerefByConstRef && Descriptor.IsTriviallyCopyable); CanCopy &&
((VarNameFromAlias && !AliasVarIsRef) ||
(Descriptor.DerefByConstRef && Descriptor.IsTriviallyCopyable));
if (!UseCopy) { if (!UseCopy) {
if (Descriptor.DerefByConstRef) { if (Descriptor.DerefByConstRef) {

12
clang-tools-extra/test/clang-tidy/modernize-loop-convert-basic.cpp
View File

@ -97,7 +97,7 @@ void f() {
// CHECK-FIXES-NEXT: Tea.g(); // CHECK-FIXES-NEXT: Tea.g();
} }
void constArray() { const int *constArray() {
for (int I = 0; I < N; ++I) { for (int I = 0; I < N; ++I) {
printf("2 * %d = %d\n", ConstArr[I], ConstArr[I] + ConstArr[I]); printf("2 * %d = %d\n", ConstArr[I], ConstArr[I] + ConstArr[I]);
} }
@ -112,6 +112,16 @@ void constArray() {
// CHECK-MESSAGES: :[[@LINE-3]]:3: warning: use range-based for loop instead // CHECK-MESSAGES: :[[@LINE-3]]:3: warning: use range-based for loop instead
// CHECK-FIXES: for (const auto & Elem : NonCopy) // CHECK-FIXES: for (const auto & Elem : NonCopy)
// CHECK-FIXES-NEXT: printf("2 * %d = %d\n", Elem.X, Elem.X + Elem.X); // CHECK-FIXES-NEXT: printf("2 * %d = %d\n", Elem.X, Elem.X + Elem.X);
bool Something = false;
for (int I = 0; I < N; ++I) {
if (Something)
return &ConstArr[I];
}
// CHECK-MESSAGES: :[[@LINE-4]]:3: warning: use range-based for loop instead
// CHECK-FIXES: for (const auto & Elem : ConstArr)
// CHECK-FIXES-NEXT: if (Something)
// CHECK-FIXES-NEXT: return &Elem;
} }
struct HasArr { struct HasArr {