[PATCH] D68672: [APInt] Rounding right-shifts

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: sanjoy, nikic, craig.topper, RKSimon.
lebedev.ri added a project: LLVM.
Herald added subscribers: dexonsmith, hiraditya.
lebedev.ri added a reviewer: timshen.
lebedev.ri marked an inline comment as done.
lebedev.ri added a subscriber: timshen.
lebedev.ri added inline comments.


================
Comment at: llvm/unittests/ADT/APIntTest.cpp:2529-2538
+        EXPECT_TRUE(Prod.sge(A));
+        if (Prod.sgt(A)) {
           EXPECT_TRUE(((Quo - 1).sext(16) * B.sext(16)).ult(A));
         }
       }
       {
         APInt Quo = APIntOps::RoundingSDiv(A, B, APInt::Rounding::DOWN);
----------------
@sanjoy @timshen FIXME: that's the intended check, right?


There's already rounding division, which is used in `ConstantRange` to
implement e.g. `makeExactMulNUWRegion()`/`makeExactMulNUWRegion()`
but there are no versions for right-shifts.
I'd like to try to extend `ConstantRange::makeGuaranteedNoWrapRegion()`
to deal with `Instruction::Shl` so i believe i need rounding right shifts.

The test coverage is confusing.
The existing `RoundingSDiv()` didn't actually pass - it never runs.
I've fixed that, and adjusted it to pass - i think we should be checking signed predicates?

Then i've added `APIntOps::RoundingLShr()`, `APIntOps::RoundingAShr()`,
standalone test coverage for them, and a cross-test to verify that
they produce identical output as compared to their `div` friends.
They do.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D68672

Files:
  llvm/include/llvm/ADT/APInt.h
  llvm/lib/Support/APInt.cpp
  llvm/unittests/ADT/APIntTest.cpp

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