[MC] Don't crash on modulo by zero (PR35650)

[RKSimon]

Summary

Extension to D12776, handle modulo by zero in the same way we handle divide by zero.

[davide]

LGTM, I didn't think about modulo when I did this for integer division, but, as you say, it's a natural extension.

llvm/trunk/lib/MC/MCExpr.cpp

case Binary: {
     // Apple as.
     int64_t LHS = LHSValue.getConstant(), RHS = RHSValue.getConstant();
     int64_t Result = 0;
     switch (ABE->getOpcode()) {
     case MCBinaryExpr::AShr: Result = LHS >> RHS; break;
     case MCBinaryExpr::Add:  Result = LHS + RHS; break;
     case MCBinaryExpr::And:  Result = LHS & RHS; break;
     case MCBinaryExpr::Div:
+    case MCBinaryExpr::Mod:
       // Handle division by zero. gas just emits a warning and keeps going,
       // we try to be stricter.
       // FIXME: Currently the caller of this function has no way to understand
       // we're bailing out because of 'division by zero'. Therefore, it will
       // emit a 'expected relocatable expression' error. It would be nice to
       // change this code to emit a better diagnostic.
       if (RHS == 0)
         return false;
+      if (ABE->getOpcode() == MCBinaryExpr::Div)
         Result = LHS / RHS;
+      else
+        Result = LHS % RHS;
       break;
     case MCBinaryExpr::EQ:   Result = LHS == RHS; break;
     case MCBinaryExpr::GT:   Result = LHS > RHS; break;
     case MCBinaryExpr::GTE:  Result = LHS >= RHS; break;
     case MCBinaryExpr::LAnd: Result = LHS && RHS; break;
     case MCBinaryExpr::LOr:  Result = LHS || RHS; break;
     case MCBinaryExpr::LShr: Result = uint64_t(LHS) >> uint64_t(RHS); break;
     case MCBinaryExpr::LT:   Result = LHS < RHS; break;
     case MCBinaryExpr::LTE:  Result = LHS <= RHS; break;
-    case MCBinaryExpr::Mod:  Result = LHS % RHS; break;
     case MCBinaryExpr::Mul:  Result = LHS * RHS; break;
     case MCBinaryExpr::NE:   Result = LHS != RHS; break;
     case MCBinaryExpr::Or:   Result = LHS | RHS; break;
     case MCBinaryExpr::Shl:  Result = uint64_t(LHS) << uint64_t(RHS); break;
     case MCBinaryExpr::Sub:  Result = LHS - RHS; break;
     case MCBinaryExpr::Xor:  Result = LHS ^ RHS; break;
     }
 

llvm/trunk/test/MC/ELF/div-by-zero.s

 // Check that llvm-mc doesn't crash on division by zero.
 // RUN: not llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s 2> %t
 // RUN: FileCheck -input-file %t %s
 
 // CHECK: expected relocatable expression
 .int 1/0
+
+// CHECK: expected relocatable expression
+.int 2%0