[clang][Interp] Diagnose shift overflows

Author: tbaederr

clang/lib/AST/Interp/Interp.h

@@ -147,7 +147,7 @@ bool CheckShift(InterpState &S, CodePtr OpPC, const LT &LHS, const RT &RHS,
     const APSInt Val = RHS.toAPSInt();
     QualType Ty = E->getType();
     S.CCEDiag(E, diag::note_constexpr_large_shift) << Val << Ty << Bits;
-    return true; // We will do the shift anyway but fix up the shift amount.
+    return !(S.getEvalStatus().Diag && !S.getEvalStatus().Diag->empty() && S.getLangOpts().CPlusPlus11);
   }
 
   if (LHS.isSigned() && !S.getLangOpts().CPlusPlus20) {

clang/test/AST/Interp/shifts.cpp

@@ -200,13 +200,14 @@ namespace LongInt {
 };
 
 enum shiftof {
-    X = (1<<-29) // all-error {{expression is not an integral constant expression}} \
-                 // all-note {{negative shift count -29}}
-};
+    X = (1<<-29), // all-error {{expression is not an integral constant expression}} \
+                  // all-note {{negative shift count -29}}
+
+    X2 = (-1<<29), // cxx17-error {{expression is not an integral constant expression}} \
+                   // cxx17-note {{left shift of negative value -1}} \
+                   // ref-cxx17-error {{expression is not an integral constant expression}} \
+                   // ref-cxx17-note {{left shift of negative value -1}}
 
-enum shiftof2 {
-    X2 = (-1<<29) // cxx17-error {{expression is not an integral constant expression}} \
-                  // cxx17-note {{left shift of negative value -1}} \
-                  // ref-cxx17-error {{expression is not an integral constant expression}} \
-                  // ref-cxx17-note {{left shift of negative value -1}}
+    X3 = (1<<32) // all-error {{expression is not an integral constant expression}} \
+                 // all-note {{shift count 32 >= width of type 'int'}}
 };