Joseph Ferano
a431cddd3b
Three arithmetic situations had no defined behaviour and the two backends disagreed about all three: a divide or remainder by zero, which was a raw SIGFPE with no message and no location; (/ min -1), whose quotient is one past the top of the type; and a float to integer cast whose value does not fit, which LLVM called undefined and would fold to anything. They now signal ArithError with `error`, exactly as a bad index signals BoundsError, and die with a sentence naming the file, the line and the operands only if nothing answered. The guards ride the same --checks flag as the bounds check and are elided with it. No restart is established at the failing operation. The sketch this started from asked for use-value, and the implementation ruled it out: a restart frame is allocated by the restart-case that offers it, on its own stack, so the runtime cannot hold one on a program's behalf and use-value here would mean an alloca and a restart frame at every division in every checked build. That is the cost already refused for indexing, buying a silently different answer. The x86 backend is unchanged and is the next commit.
