[gcc r12-7922] c-family: ICE with -Wconversion and A ?: B [PR101030]

[gcc r12-7922] c-family: ICE with -Wconversion and A ?: B [PR101030]

[Marek Polacek]

https://gcc.gnu.org/g:5db9ce171019f8915885cebd5cc5f4101bb926e6

commit r12-7922-g5db9ce171019f8915885cebd5cc5f4101bb926e6
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue Mar 29 14:36:55 2022 -0400

    c-family: ICE with -Wconversion and A ?: B [PR101030]
    
    This patch fixes a crash in conversion_warning on a null expression.
    It is null because the testcase uses the GNU A ?: B extension.  We
    could also use op0 instead of op1 in this case, but it doesn't seem
    to be necessary.
    
            PR c++/101030
    
    gcc/c-family/ChangeLog:
    
            * c-warn.cc (conversion_warning) <case COND_EXPR>: Don't call
            conversion_warning when OP1 is null.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/ext/cond5.C: New test.

Diff:
---
 gcc/c-family/c-warn.cc           |  2 +-
 gcc/testsuite/g++.dg/ext/cond5.C | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/gcc/c-family/c-warn.cc b/gcc/c-family/c-warn.cc
index 9025fc1c20e..f24ac5d0539 100644
--- a/gcc/c-family/c-warn.cc
+++ b/gcc/c-family/c-warn.cc
@@ -1300,7 +1300,7 @@ conversion_warning (location_t loc, tree type, tree expr, tree result)
 	tree op1 = TREE_OPERAND (expr, 1);
 	tree op2 = TREE_OPERAND (expr, 2);
 
-	return (conversion_warning (loc, type, op1, result)
+	return ((op1 && conversion_warning (loc, type, op1, result))
 		|| conversion_warning (loc, type, op2, result));
       }
 
diff --git a/gcc/testsuite/g++.dg/ext/cond5.C b/gcc/testsuite/g++.dg/ext/cond5.C
new file mode 100644
index 00000000000..a92f28998f9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/cond5.C
@@ -0,0 +1,13 @@
+// PR c++/101030
+// { dg-do compile { target { c++11 } } }
+// { dg-options "-Wconversion" }
+
+template <int N>
+struct jj {
+    int ii[N ?: 1];
+    char c = N ?: 1; // { dg-warning "conversion from .int. to .char. changes value from .300. to " }
+};
+
+int main() {
+    jj<300> kk;
+}