[llvm-dev] urem instruction

[Vadim Zaliva via llvm-dev]

I have a question about the semantics of the "urem a b" IR instruction when "a/b" is not representable.

The language reference states that "This instruction returns the unsigned integer remainder of a division.
This instruction always performs an unsigned division to get the remainder."

It does not specify what it returns in if a/b is not representable. For example "udiv" definition says:
"If the exact keyword is present, the result value of the udiv is a poison value
if %op1 is not a multiple of %op2 (as such, "((a udiv exact b) mul b) == a")."

So it is internally calling "exact udiv", the poison value returned by it will cause "udev" return value to be a poison.
However, if it is not using "exact," I am not sure what the result would be.

Could somebody clarify the intended semantics or "urem" for me? Thanks!

Vadim

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