Fix CQ regression & correctness bug in morphing of long muls #53566
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To understand the new format for long muls.
Previously, morph was looking for the exact pattern of MUL(CAST(long <- int), CAST(long <- int)) when assessing candidacy of GT_MUL for being marked with "GTF_MUL_64RSLT" and emitted as "long mul". This worked fine, until the importer was changed to fold all casts with constant operands. This broke the pattern matching and thus all MULs in the form of (long)value * 10 started being emitted as helper calls. This change updates morph to understand the new folded casts and in general updates the "format" of long mul from "CAST * CAST" to "CAST * (CAST | CONST)". In the process, new helper functions have been introduced, to avoid bloating fgMorphSmpOp with the new sizeable logic. Recognition of overflowing cases has been upgraded, and a correctness bug, where "checked((long)uint.MaxValue * (long)uint.MaxValue)" was wrongly treated as non-overflowing, fixed. Additionally, the logic to emit intermediate NOPs has been changed to instead always skip morphing the casts themselves, even when remorphing.
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Marking as ready for review, the failure is unrelated (no tests ran and python crashed at the end). cc @sandreenko - more morph changes... |
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PTAL @dotnet/jit-contrib , I probably won't have time to review it this week. |
Perhaps. I am in the process of experimenting with moving most of the "morph to helpers" logic to lowering, so that we don't have to play tricks like completely blocking long mul trees from assertion propagation for correctness reasons. If that fails (fairly likely given it is not so trivial to add new calls that late), I will of course update all the places that use the flag today to use the helpers. Speaking of flags, I will have to rebase so as not to fail the build now that we have to use
Sounds good to me, and there's precedent in the |
The test itself has been regenerated using it and there were no diffs, as expected.
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Previously, morph was looking for the exact pattern of
MUL(CAST(long <- int), CAST(long <- int))when assessingcandidacy of
GT_MULfor being marked withGTF_MUL_64RSLTand emitted as "long mul".This worked fine, until the importer was changed to fold all casts with constant operands. This broke the pattern matching and thus all
MULs in the form of(long)value * 10started being emitted as helper calls.This change updates morph to understand the new folded casts and in general updates the "format" of long mul from
CAST * CASTtoCAST * (CAST | CONST).In the process, new helper functions have been introduced, to avoid bloating
fgMorphSmpOpwith the new sizeable logic.Recognition of overflowing cases has been upgraded, and a correctness bug, where
checked((long)uint.MaxValue * (long)uint.MaxValue)was wrongly treated as non-overflowing, fixed.Additionally, the logic to emit intermediate
NOPs has been changed to instead always skip morphing the casts themselves,even when remorphing.
A new test has been added, generated via a script. The test is meant to be an outerloop one, but I am temporarily marking it Pri0 for it to run in CI.
Also, a few helpers for working with
gtFlagshave been added.Diffs for this change:
Windows x86
Linux ARM
Most regressions are caused by the fact that the new code doesn't try to look for
CAST(CONST), and that is impactful for cases when we emit debuggable code - it now goes through the helper. Because there are so few regressions, and they are for debuggable code only, I decided not to complicate the code by fixing it. The<ReadHeadersAsync>d__43:MoveNext()regression is caused by different register allocation, even as the helper call was turned intoimul. One of the regressions onARMis caused by a lack of CSE.