C++ PATCH for c++/91740 - ICE with constexpr call and ?: in ARRAY_REF

Message ID 20190911211527.GM14737@redhat.com
State New
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  • C++ PATCH for c++/91740 - ICE with constexpr call and ?: in ARRAY_REF
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Commit Message

Marek Polacek Sept. 11, 2019, 9:15 p.m.
This ICEs since r267272 - more location wrapper nodes, but not because we can't
cope with new location wrappers, but because that commit introduced a call to
maybe_constant_value in cp_build_array_ref.  In this testcase we call it with

  f (VIEW_CONVERT_EXPR<const char[4]>("BAR")) ? 1 : 0

argument and that crashes in fold_convert because we end up trying to convert 
"BAR" of type const char[4] to const char * when evaluating the call.  At this
point, decay_conversion hasn't turned the argument into (const char *) "BAR"
yet.

The ICE doesn't occur without :?, because then the call will be wrapped in
NON_DEPENDENT_EXPR and constexpr throws its hands (I'm anthropomorphizing) up
when it encounters such an expression.

I noticed that build_non_dependent_expr doesn't wrap op0 of ?: in N_D_E.  This
is so since r70606 -- Nathan, is there a reason not to do it?  Doing it fixes
this problem.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2019-09-11  Marek Polacek  <polacek@redhat.com>

	PR c++/91740 - ICE with constexpr call and ?: in ARRAY_REF.
	* pt.c (build_non_dependent_expr): Call build_non_dependent_expr for
	the first operand.

	* g++.dg/cpp1y/var-templ63.C: New test.

Comments

Paolo Carlini Sept. 12, 2019, 9:03 a.m. | #1
Hi,

On 11/09/19 23:15, Marek Polacek wrote:
> --- gcc/cp/pt.c

> +++ gcc/cp/pt.c

> @@ -26709,7 +26709,7 @@ build_non_dependent_expr (tree expr)

>     if (TREE_CODE (expr) == COND_EXPR)

>       return build3 (COND_EXPR,

>   		   TREE_TYPE (expr),

> -		   TREE_OPERAND (expr, 0),

> +		   build_non_dependent_expr (TREE_OPERAND (expr, 0)),

>   		   (TREE_OPERAND (expr, 1)

>   		    ? build_non_dependent_expr (TREE_OPERAND (expr, 1))

>   		    : build_non_dependent_expr (TREE_OPERAND (expr, 0))),


Looks like we would end up unnecessarily calling 
build_non_dependent_expr three times instead of two: probably is very 
cheap, probably the code is cleaner this way but I'm a little annoyed at 
this anyway, for the record ;)

Cheers, Paolo.
Paolo Carlini Sept. 12, 2019, 9:08 a.m. | #2
Hi again,

On 12/09/19 11:03, Paolo Carlini wrote:
> Hi,

>

> On 11/09/19 23:15, Marek Polacek wrote:

>> --- gcc/cp/pt.c

>> +++ gcc/cp/pt.c

>> @@ -26709,7 +26709,7 @@ build_non_dependent_expr (tree expr)

>>     if (TREE_CODE (expr) == COND_EXPR)

>>       return build3 (COND_EXPR,

>>              TREE_TYPE (expr),

>> -           TREE_OPERAND (expr, 0),

>> +           build_non_dependent_expr (TREE_OPERAND (expr, 0)),

>>              (TREE_OPERAND (expr, 1)

>>               ? build_non_dependent_expr (TREE_OPERAND (expr, 1))

>>               : build_non_dependent_expr (TREE_OPERAND (expr, 0))),

>

> Looks like we would end up unnecessarily calling 

> build_non_dependent_expr three times instead of two: probably is very 

> cheap, probably the code is cleaner this way but I'm a little annoyed 

> at this anyway, for the record ;)


Sorry, I misread the code: normally TREE_OPERAND (expr, 1) isn't 
NULL_TREE thus we are fine.

Paolo.
Marek Polacek Sept. 12, 2019, 11:03 a.m. | #3
On Thu, Sep 12, 2019 at 11:08:43AM +0200, Paolo Carlini wrote:
> Hi again,

> 

> On 12/09/19 11:03, Paolo Carlini wrote:

> > Hi,

> > 

> > On 11/09/19 23:15, Marek Polacek wrote:

> > > --- gcc/cp/pt.c

> > > +++ gcc/cp/pt.c

> > > @@ -26709,7 +26709,7 @@ build_non_dependent_expr (tree expr)

> > >     if (TREE_CODE (expr) == COND_EXPR)

> > >       return build3 (COND_EXPR,

> > >              TREE_TYPE (expr),

> > > -           TREE_OPERAND (expr, 0),

> > > +           build_non_dependent_expr (TREE_OPERAND (expr, 0)),

> > >              (TREE_OPERAND (expr, 1)

> > >               ? build_non_dependent_expr (TREE_OPERAND (expr, 1))

> > >               : build_non_dependent_expr (TREE_OPERAND (expr, 0))),

> > 

> > Looks like we would end up unnecessarily calling

> > build_non_dependent_expr three times instead of two: probably is very

> > cheap, probably the code is cleaner this way but I'm a little annoyed at

> > this anyway, for the record ;)

> 

> Sorry, I misread the code: normally TREE_OPERAND (expr, 1) isn't NULL_TREE

> thus we are fine.


And I forgot to mention that build_x_conditional_expr has

 6743       ifexp = build_non_dependent_expr (ifexp);
 6744       if (op1)
 6745         op1 = build_non_dependent_expr (op1);
 6746       op2 = build_non_dependent_expr (op2);

which means my fix should make more sense. 

--
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA
Jason Merrill Sept. 15, 2019, 2:26 p.m. | #4
On 9/11/19 4:15 PM, Marek Polacek wrote:
> This ICEs since r267272 - more location wrapper nodes, but not because we can't

> cope with new location wrappers, but because that commit introduced a call to

> maybe_constant_value in cp_build_array_ref.  In this testcase we call it with

> 

>    f (VIEW_CONVERT_EXPR<const char[4]>("BAR")) ? 1 : 0

> 

> argument and that crashes in fold_convert because we end up trying to convert

> "BAR" of type const char[4] to const char * when evaluating the call.  At this

> point, decay_conversion hasn't turned the argument into (const char *) "BAR"

> yet.

> 

> The ICE doesn't occur without :?, because then the call will be wrapped in

> NON_DEPENDENT_EXPR and constexpr throws its hands (I'm anthropomorphizing) up

> when it encounters such an expression.

> 

> I noticed that build_non_dependent_expr doesn't wrap op0 of ?: in N_D_E.  This

> is so since r70606 -- Nathan, is there a reason not to do it?  Doing it fixes

> this problem.

> 

> Bootstrapped/regtested on x86_64-linux, ok for trunk?

> 

> 2019-09-11  Marek Polacek  <polacek@redhat.com>

> 

> 	PR c++/91740 - ICE with constexpr call and ?: in ARRAY_REF.

> 	* pt.c (build_non_dependent_expr): Call build_non_dependent_expr for

> 	the first operand.

> 

> 	* g++.dg/cpp1y/var-templ63.C: New test.

> 

> diff --git gcc/cp/pt.c gcc/cp/pt.c

> index c5915a5ecd0..775389d8245 100644

> --- gcc/cp/pt.c

> +++ gcc/cp/pt.c

> @@ -26709,7 +26709,7 @@ build_non_dependent_expr (tree expr)

>     if (TREE_CODE (expr) == COND_EXPR)

>       return build3 (COND_EXPR,

>   		   TREE_TYPE (expr),

> -		   TREE_OPERAND (expr, 0),

> +		   build_non_dependent_expr (TREE_OPERAND (expr, 0)),

>   		   (TREE_OPERAND (expr, 1)

>   		    ? build_non_dependent_expr (TREE_OPERAND (expr, 1))

>   		    : build_non_dependent_expr (TREE_OPERAND (expr, 0))),


OK.  I wonder why this code copies op0 for the ?: extension rather than 
leave it null?

Jason

Patch

diff --git gcc/cp/pt.c gcc/cp/pt.c
index c5915a5ecd0..775389d8245 100644
--- gcc/cp/pt.c
+++ gcc/cp/pt.c
@@ -26709,7 +26709,7 @@  build_non_dependent_expr (tree expr)
   if (TREE_CODE (expr) == COND_EXPR)
     return build3 (COND_EXPR,
 		   TREE_TYPE (expr),
-		   TREE_OPERAND (expr, 0),
+		   build_non_dependent_expr (TREE_OPERAND (expr, 0)),
 		   (TREE_OPERAND (expr, 1)
 		    ? build_non_dependent_expr (TREE_OPERAND (expr, 1))
 		    : build_non_dependent_expr (TREE_OPERAND (expr, 0))),
diff --git gcc/testsuite/g++.dg/cpp1y/var-templ63.C gcc/testsuite/g++.dg/cpp1y/var-templ63.C
new file mode 100644
index 00000000000..a65f53b2963
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp1y/var-templ63.C
@@ -0,0 +1,5 @@ 
+// PR c++/91740 - ICE with constexpr call and ?: in ARRAY_REF.
+// { dg-do compile { target c++14 } }
+
+constexpr bool f(const char*) { return true; }
+template<typename T> const char c = "FOO"[f("BAR") ? 1 : 0];