Warn on always false integer reads and comparisons. #1919
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When reading an integer of a specific size and comparing it to an integer of a larger size where any of the upper bits are set we will now emit a warning because the comparison is always false. These will always evaluate to false because the "extra" bytes are non-zero: uint8(0) == 0x1100 uint16(0) == 0x110000 uint32(0) == 0x1100000000 While I'm here, move a test into a better place for it. I added it in the wrong place in ccbc405. Fixes VirusTotal#1918.
Turns out that my first implementation of this was flawed. Things like uint8(uint8(0)) would cause an error. To make this a bit easier to follow I changed the lexer return tokens for each of the integer functions, instead of a single _INTEGER_FUNCTION_ token with an index value to use when emiting the opcode. By doing this I can then set the width of the expression based upon the new token types and use that when doing the width check (instead of inferring the width from the index). Once we have reduced the integer_function we can set it to an integer with an undefined value and it will be treated like a normal integer for all operations, except for _EQ_, which has special case logic to check the width and any compile-time values.
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When reading an integer of a specific size and comparing it to an integer of a larger size where any of the upper bits are set we will now emit a warning because the comparison is always false.
These will always evaluate to false because the "extra" bytes are non-zero:
uint8(0) == 0x1100
uint16(0) == 0x110000
uint32(0) == 0x1100000000
While I'm here, move a test into a better place for it. I added it in the wrong place in ccbc405.
Fixes #1918.