pytorch

e1ee10e6 - Add expect_true for irrefutable guards (#106720)

Add expect_true for irrefutable guards (#106720) Here's what it does from the comments: ``` Assume that a boolean is true for the purposes of subsequent symbolic reasoning. This will keep track of corresponding runtime checks to verify that the result is upheld: either as a regular guard, or as a special set of asserts which are triggered when an unbacked SymInt is allocated. DO NOT use this function for these cases: - This is inappropriate for "branching" conditions (where both true and false result in valid programs). We will always assume the condition evaluates true, and so it will never be possible to trace the false condition when you use it. For true branching on unbacked SymInts, you must use torch.cond. - This is inappropriate for situations where you know some other system invariant guarantees that this property holds, since you don't really need to insert a runtime check in that case. Use something like constrain_range in that case. This API has a hitch. To avoid having to reimplement error reporting capabilities, this function CAN return False. The invariant is that the surrounding code must raise an error when this function returns False. This is quite low level, so we recommend using other functions like check() which enforce this in a more intuitive way. By the way, this name is a nod to the __builtin_expect likely macro, which is used similarly (but unlike __builtin_expect, you MUST fail in the unlikely branch.) ``` We don't do anything with this right now, except use it to discharge regular guards. Follow up PRs to (1) use it at important error checking sites, (2) actually ensure the runtime asserts make there way into the exported IR / inductor generated code. Signed-off-by: Edward Z. Yang <ezyang@meta.com> Pull Request resolved: https://github.com/pytorch/pytorch/pull/106720 Approved by: https://github.com/ysiraichi, https://github.com/voznesenskym