[Sema] Validate calls to GetExprRange.

When a conditional expression has a throw expression it called
GetExprRange with a void expression, which caused an assertion failure.

This approach was suggested by Richard Smith.

Fixes PR46484: Clang crash in clang/lib/Sema/SemaChecking.cpp:10028

Differential Revision: https://reviews.llvm.org/D85601

clang/lib/Sema/SemaChecking.cpp

@@ -10368,10 +10368,16 @@ static IntRange GetExprRange(ASTContext &C, const Expr *E, unsigned MaxWidth,
                           MaxWidth, InConstantContext);
 
     // Otherwise, conservatively merge.
-    IntRange L =
-        GetExprRange(C, CO->getTrueExpr(), MaxWidth, InConstantContext);
-    IntRange R =
-        GetExprRange(C, CO->getFalseExpr(), MaxWidth, InConstantContext);
+    // GetExprRange requires an integer expression, but a throw expression
+    // results in a void type.
+    Expr *E = CO->getTrueExpr();
+    IntRange L = E->getType()->isVoidType()
+                     ? IntRange{0, true}
+                     : GetExprRange(C, E, MaxWidth, InConstantContext);
+    E = CO->getFalseExpr();
+    IntRange R = E->getType()->isVoidType()
+                     ? IntRange{0, true}
+                     : GetExprRange(C, E, MaxWidth, InConstantContext);
     return IntRange::join(L, R);
   }
 

clang/test/SemaCXX/conditional-expr.cpp

@@ -409,3 +409,20 @@ namespace lifetime_extension {
     D d = b ? D{B()} : D{C()};
   }
 }
+
+namespace PR46484 {
+// expected-error@+4{{expected ':'}}
+// expected-note@+3{{to match this '?'}}
+// expected-warning@+2{{variable 'b' is uninitialized}}
+// expected-error@+1 2 {{expected ';' after top level declarator}}
+int a long b = a = b ? throw 0 1
+
+void g() {
+  extern int a;
+  extern long b;
+  long c = a = b ? throw 0 : 1;
+  long d = a = b ? 1 : throw 0;
+  // expected-error@+1 {{assigning to 'int' from incompatible type 'void'}}
+  long e = a = b ? throw 0 : throw 1;
+}
+} // namespace PR46484