Ping^2... Il 29/08/2015 10:01, Abramo Bagnara ha scritto: > Il 28/08/2015 23:27, Richard Smith ha scritto: >> On Tue, Aug 25, 2015 at 10:27 AM, Abramo Bagnara >> <abramo.bagn...@bugseng.com <mailto:abramo.bagn...@bugseng.com>> wrote: >> >> Comparing the result of InitListExpr::getSyntacticForm between r224986 >> and r245836 I've discovered that integer to char implicit cast for >> integer literal 3 is no longer added to AST for C++ (while it is present >> in C). >> >> This is the source used to test: >> >> char v[10] = { 3 }; >> >> Taken in account that: >> >> - implicit cast (and other conversions, constructor calls, etc.) are >> very important also for who need to visit the syntactic form (obvious in >> *both* C and C++) >> >> - to generate that for the syntactic form permit to increase the >> efficiency and the sharing when using designated range extensions (as >> the conversion chain don't need to be replicated for each entry) >> >> I think it is a regression. Am I missing something? >> >> >> Why do you expect this semantic information to appear in the syntactic >> form of the initializer? > > Compare: > > int x = 2.0; > > with > > struct s { > int x; > } v = { .x = 2.0 }; > > For first declaration I have non-syntactic nodes (namely > ImplicitCastExpr) along with syntactic nodes, while for the second I > don't have that (for C++). This is an obstacle to write semi-syntactic > checkers that aims to find e.g. implicit cast from double to int in its > syntactic context. > Note that although we might visit the semantic form, we'll lose the > designators (not present in semantic form). > > To resume, the reason why I would expect that are: > > 1) this is how it always has worked for C (and fortunately still works > this way) > > > 2) this is how it always has worked (although partially, there was some > bugs) for C++. In past we have had patches to fix the areas where this > invariant was not respected (see commit 3146766 > http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20111212/050339.html > as an example). > > This behavior has changed rather recently (if you think it is useful I > can find the commit that has removed the implicit casts from syntactic > form in C++) > > Before such commit(s) the only bug I was aware where AST was missing > conversion chain was the following: > > struct R2 { > R2(int) { > } > }; > R2 v2[] = { 1.0 }; > > > 3) this way it would be congruent with other areas of AST where we have > non-syntactic nodes along with syntactic ones > > > 4) it would permit to share more nodes in semantic form (and avoid to > rebuild many times the same conversion chain). > > Looking at following typescript you can observe that ImplicitCastExpr is > shared only for C, but not for C++. I've initialized only two entries, > but it might be 1000 or 10000000. > > $ cat p.c > int x[1000000] = { [0 ... 1] = 3.0 }; > $ clang-3.8 -cc1 -ast-dump -x c p.c > TranslationUnitDecl 0x272de40 <<invalid sloc>> <invalid sloc> > |-TypedefDecl 0x272e338 <<invalid sloc>> <invalid sloc> implicit > __int128_t '__int128' > |-TypedefDecl 0x272e398 <<invalid sloc>> <invalid sloc> implicit > __uint128_t 'unsigned __int128' > |-TypedefDecl 0x272e648 <<invalid sloc>> <invalid sloc> implicit > __builtin_va_list 'struct __va_list_tag [1]' > `-VarDecl 0x272e718 <p.c:1:1, col:36> col:5 x 'int [1000000]' cinit > `-InitListExpr 0x272e8b0 <col:18, col:36> 'int [1000000]' > |-array filler > | `-ImplicitValueInitExpr 0x272e918 <<invalid sloc>> 'int' > |-ImplicitCastExpr 0x272e900 <col:32> 'int' <FloatingToIntegral> > | `-FloatingLiteral 0x272e7f8 <col:32> 'double' 3.000000e+00 > `-ImplicitCastExpr 0x272e900 <col:32> 'int' <FloatingToIntegral> > `-FloatingLiteral 0x272e7f8 <col:32> 'double' 3.000000e+00 > $ clang-3.8 -cc1 -ast-dump -x c++ p.c > TranslationUnitDecl 0x3300e60 <<invalid sloc>> <invalid sloc> > |-TypedefDecl 0x3301398 <<invalid sloc>> <invalid sloc> implicit > __int128_t '__int128' > |-TypedefDecl 0x33013f8 <<invalid sloc>> <invalid sloc> implicit > __uint128_t 'unsigned __int128' > |-TypedefDecl 0x3301718 <<invalid sloc>> <invalid sloc> implicit > __builtin_va_list 'struct __va_list_tag [1]' > `-VarDecl 0x33017e8 <p.c:1:1, col:36> col:5 x 'int [1000000]' cinit > `-InitListExpr 0x3301980 <col:18, col:36> 'int [1000000]' > |-array filler > | `-ImplicitValueInitExpr 0x3301a00 <<invalid sloc>> 'int' > |-ImplicitCastExpr 0x33019d0 <col:32> 'int' <FloatingToIntegral> > | `-FloatingLiteral 0x33018c8 <col:32> 'double' 3.000000e+00 > `-ImplicitCastExpr 0x33019e8 <col:32> 'int' <FloatingToIntegral> > `-FloatingLiteral 0x33018c8 <col:32> 'double' 3.000000e+00 > > > 5) if we would visit semantic form in a checker searching for implicit > cast from float to int in the C source above we'll find *two* of them, > while syntactically we have only one. This means that we should be > forced do some dirty tricks to avoid double reporting. >
-- Abramo Bagnara BUGSENG srl - http://bugseng.com mailto:abramo.bagn...@bugseng.com _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
