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[AST] Pick last tentative definition as the acting definition 

Clang currently picks the second tentative definition when
VarDecl::getActingDefinition is called.

This can lead to attributes being dropped if they are attached to
tentative definitions that appear after the second one. This is
because VarDecl::getActingDefinition loops through VarDecl::redecls
assuming that the last tentative definition is the last element in the
iterator. However, it is the second element that would be the last
tentative definition.

This changeset modifies getActingDefinition to iterate through the
declaration chain in reverse, so that it can immediately return when
it encounters a tentative definition.

Differential Revision: https://reviews.llvm.org/D99732
This commit is contained in:
Benson Chu 2021-08-15 13:12:21 -05:00
parent 6de0b55188
commit 9a5f388850
2 changed files with 16 additions and 5 deletions
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14
clang/lib/AST/Decl.cpp
View File

@ -2216,14 +2216,18 @@ VarDecl *VarDecl::getActingDefinition() {
return nullptr;
VarDecl *LastTentative = nullptr;
VarDecl *First = getFirstDecl();
for (auto I : First->redecls()) {
Kind = I->isThisDeclarationADefinition();
// Loop through the declaration chain, starting with the most recent.
for (VarDecl *Decl = getMostRecentDecl(); Decl;
Decl = Decl->getPreviousDecl()) {
Kind = Decl->isThisDeclarationADefinition();
if (Kind == Definition)
return nullptr;
if (Kind == TentativeDefinition)
LastTentative = I;
// Record the first (most recent) TentativeDefinition that is encountered.
if (Kind == TentativeDefinition && !LastTentative)
LastTentative = Decl;
}
return LastTentative;
}

7
clang/test/CodeGen/attr-tentative-definition.c Normal file
View File

@ -0,0 +1,7 @@
// RUN: %clang_cc1 -emit-llvm < %s | FileCheck %s
char arr[10];
char arr[10] __attribute__((section("datadata")));
char arr[10] __attribute__((aligned(16)));
// CHECK: @arr ={{.*}}section "datadata", align 16