[PATCH] D21645: [CFLAA] Propagate StratifiedAttrs from callee to caller

[Hans-Bernhard Bröker via llvm-commits]

Hello,

and please excuse my barging in like this.  I think one detail of the 
recent patch r273636 is wrong.  The shift operation in

static StratifiedAttrs argNumberToAttr(unsigned ArgNum) {
   if (ArgNum >= AttrMaxNumArgs)
     return AttrUnknown;
   return StratifiedAttrs(1 << (ArgNum + AttrFirstArgIndex));
}

is fishy, and MSVC rightly warns about it:

  [...]\llvm\lib\Analysis\CFLAliasAnalysis.cpp(765): warning C4334: 
'<<': result of 32-bit shift implicitly converted to 64 bits (was 64-bit 
shift intended?)

The problem is that the literal '1', and thus the result of the shift, 
is a plain signed int, whereas the constructor of StatifiedAttrs() takes 
an argument of unsigned long long.  On 64-bit Windows, these are 32-bit 
signed and 64-bit unsigned, respectively, hence the warning.

Shifts like that should always be done entirely in the realm of unsigned 
numbers, i.e. that should be `1U' instead of `1'.  And if the result is 
going to end up being implicitly converted to long long, it's best to 
write it as that directly:

   return StratifiedAttrs(1ULL << (ArgNum + AttrFirstArgIndex));

Hans-Bernhard Bröker