[llvm] Add KnownBits implementations for avgFloor and avgCeil #86445

changkhothuychung · 2024-03-24T17:55:49Z

This PR is to address the issue #84640

llvmbot · 2024-03-24T17:56:17Z

@llvm/pr-subscribers-llvm-selectiondag

@llvm/pr-subscribers-llvm-support

Author: Nhat Nguyen (changkhothuychung)

Changes

This PR is to address the issue #84640

Full diff: https://github.com/llvm/llvm-project/pull/86445.diff

1 Files Affected:

(modified) llvm/lib/Support/KnownBits.cpp (+40)

diff --git a/llvm/lib/Support/KnownBits.cpp b/llvm/lib/Support/KnownBits.cpp
index d72355dab6f1d3..07c7ad0882387a 100644
--- a/llvm/lib/Support/KnownBits.cpp
+++ b/llvm/lib/Support/KnownBits.cpp
@@ -762,6 +762,46 @@ KnownBits KnownBits::usub_sat(const KnownBits &LHS, const KnownBits &RHS) {
   return computeForSatAddSub(/*Add*/ false, /*Signed*/ false, LHS, RHS);
 }
 
+KnownBits KnownBits::avgFloorS(const KnownBits &LHS, const KnownBits &RHS) {
+  // (C1 & C2) + (C1 ^ C2).ashr(1)
+  KnownBits andResult = LHS & RHS;
+  KnownBits xorResult = LHS ^ RHS;
+  xorResult.Zero.ashrInPlace(1);
+  xorResult.One.ashrInPlace(1);
+  return computeForSatAddSub(/*Add*/ true, /*Signed*/ true, andResult,
+                             xorResult);
+}
+
+KnownBits KnownBits::avgFloorU(const KnownBits &LHS, const KnownBits &RHS) {
+  // (C1 & C2) + (C1 ^ C2).lshr(1)
+  KnownBits andResult = LHS & RHS;
+  KnownBits xorResult = LHS ^ RHS;
+  xorResult.Zero.lshrInPlace(1);
+  xorResult.One.lshrInPlace(1);
+  return computeForSatAddSub(/*Add*/ true, /*Signed*/ false, andResult,
+                             xorResult);
+}
+
+KnownBits KnownBits::avgCeilS(const KnownBits &LHS, const KnownBits &RHS) {
+  // (C1 | C2) - (C1 ^ C2).ashr(1)
+  KnownBits andResult = LHS & RHS;
+  KnownBits xorResult = LHS ^ RHS;
+  xorResult.Zero.ashrInPlace(1);
+  xorResult.One.ashrInPlace(1);
+  return computeForSatAddSub(/*Add*/ false, /*Signed*/ true, andResult,
+                             xorResult);
+}
+
+KnownBits KnownBits::avgCeilU(const KnownBits &LHS, const KnownBits &RHS) {
+  // (C1 | C2) - (C1 ^ C2).lshr(1)
+  KnownBits andResult = LHS & RHS;
+  KnownBits xorResult = LHS ^ RHS;
+  xorResult.Zero.lshrInPlace(1);
+  xorResult.One.lshrInPlace(1);
+  return computeForSatAddSub(/*Add*/ false, /*Signed*/ false, andResult,
+                             xorResult);
+}
+
 KnownBits KnownBits::mul(const KnownBits &LHS, const KnownBits &RHS,
                          bool NoUndefSelfMultiply) {
   unsigned BitWidth = LHS.getBitWidth();

github-actions · 2024-03-24T17:58:47Z

✅ With the latest revision this PR passed the Python code formatter.

github-actions · 2024-03-24T17:58:47Z

✅ With the latest revision this PR passed the C/C++ code formatter.

changkhothuychung · 2024-03-24T18:34:53Z

@RKSimon RkSim
What type of test should I add, should it be similar to this test ?

llvm-project/llvm/unittests/Support/KnownBitsTest.cpp

Lines 834 to 848 in ffe4181

    
           TEST(KnownBitsTest, CommonBitsSet) { 
        
             unsigned Bits = 4; 
        
             ForeachKnownBits(Bits, [&](const KnownBits &Known1) { 
        
               ForeachKnownBits(Bits, [&](const KnownBits &Known2) { 
        
                 bool HasCommonBitsSet = false; 
        
                 ForeachNumInKnownBits(Known1, [&](const APInt &N1) { 
        
                   ForeachNumInKnownBits(Known2, [&](const APInt &N2) { 
        
                     HasCommonBitsSet |= N1.intersects(N2); 
        
                   }); 
        
                 }); 
        
                 EXPECT_EQ(!HasCommonBitsSet, 
        
                           KnownBits::haveNoCommonBitsSet(Known1, Known2)); 
        
               }); 
        
             }); 
        
           }

changkhothuychung · 2024-03-30T18:15:59Z

@RKSimon Rkso
just following up on this!

goldsteinn · 2024-04-01T16:23:18Z

@RKSimon RkSim What type of test should I add, should it be similar to this test ?

llvm-project/llvm/unittests/Support/KnownBitsTest.cpp

Lines 834 to 848 in ffe4181

TEST(KnownBitsTest, CommonBitsSet) {

unsigned Bits = 4;

ForeachKnownBits(Bits, [&](const KnownBits &Known1) {

ForeachKnownBits(Bits, [&](const KnownBits &Known2) {

bool HasCommonBitsSet = false;

ForeachNumInKnownBits(Known1, [&](const APInt &N1) {

ForeachNumInKnownBits(Known2, [&](const APInt &N2) {

HasCommonBitsSet |= N1.intersects(N2);

});

});

EXPECT_EQ(!HasCommonBitsSet,

KnownBits::haveNoCommonBitsSet(Known1, Known2));

});

});

}

Your unit tests should look something like:

  testBinaryOpExhaustive(KnownBits::abds, APIntOps::abds,
                         checkCorrectnessOnlyBinary);

The first argument is a function pointer to the knownbits function we are testing.
The second argument is a function pointer to the reference implementation on an APInt.
edit: both of the function pointers can be lambda's i.e:

  testBinaryOpExhaustive(
      [](const KnownBits &Known1, const KnownBits &Known2) {
        return KnownBits::udiv(Known1, Known2);
      },
      [](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
        if (N2.isZero())
          return std::nullopt;
        return N1.udiv(N2);
      },
      checkCorrectnessOnlyBinary);

The third is optional. If your implementation is complete (i.e proves all knowable bits) you can
drop it, otherwise just use what you see above. We like to strive for exhaustive, so if yours is not,
can you provide a few values that is fails for and explain a bit why its not really feasible?

llvm/lib/Support/KnownBits.cpp

llvm/include/llvm/Support/KnownBits.h

RKSimon

#86754 has now landed so please can you update the SelectionDAG::computeKnownBits AVG cases to use KnowBits implementations

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

llvm/lib/Support/KnownBits.cpp

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

llvm/unittests/Support/KnownBitsTest.cpp

RKSimon

Please address the KnownBitsTests failures

llvm/lib/Support/KnownBits.cpp

jayfoad · 2024-04-08T03:57:04Z

llvm/lib/Support/KnownBits.cpp

+
+KnownBits KnownBits::avgCeilS(const KnownBits &LHS, const KnownBits &RHS) {
+  // (C1 | C2) - (C1 ^ C2).ashr(1)
+  KnownBits andResult = LHS | RHS;


Change name to OrResult. Variable names should be capitalised throughout.

jayfoad · 2024-04-08T03:58:15Z

llvm/include/llvm/Support/KnownBits.h

+  /// Compute knownbits resulting from APIntOps::avgFloorU
+  static KnownBits avgFloorU(const KnownBits &LHS, const KnownBits &RHS);
+
+  /// Compute knownbits resulting from APIntOps::avgCelS


Typo "Cel" here and below

avgCel -> avgCeil

llvm/include/llvm/Support/KnownBits.h

llvm/lib/Support/KnownBits.cpp

llvm/unittests/Support/KnownBitsTest.cpp

jayfoad

This looks good to me now except for the remaining cosmetic issues.

llvm/lib/Support/KnownBits.cpp

goldsteinn · 2024-05-17T15:32:39Z

This LGTM, wait one 1 more approval to push.

jayfoad · 2024-05-17T15:48:06Z

llvm/lib/Support/KnownBits.cpp

@@ -475,7 +475,7 @@ KnownBits KnownBits::ashr(const KnownBits &LHS, const KnownBits &RHS,
  Known.Zero.setAllBits();
  Known.One.setAllBits();
  for (unsigned ShiftAmt = MinShiftAmount; ShiftAmt <= MaxShiftAmount;
-      ++ShiftAmt) {
+       ++ShiftAmt) {


This looks like spurious reformatting.

changkhothuychung · 2024-05-17T16:01:23Z

@jayfoad f
looks like the BinaryExhaustive test fails when I remove the bool flag to enable Optimal check?

Link to failed CI: https://buildkite.com/llvm-project/github-pull-requests/builds/65024#018f86e0-35f7-4c66-bb68-14cd36220d70

jayfoad · 2024-05-17T16:06:15Z

looks like the BinaryExhaustive test fails when I remove the bool flag to enable Optimal check?

Oh, I thought this implementation was supposed to be optimal, but maybe I got that wrong.

Patch LGTM anyway.

jayfoad · 2024-05-17T16:18:32Z

looks like the BinaryExhaustive test fails when I remove the bool flag to enable Optimal check?

Oh, I thought this implementation was supposed to be optimal, but maybe I got that wrong.

Having looked into it, the unsigned functions are optimal. The signed ones are not because LHS/RHS.sext(BitWidth + 1) does not preserve the knowledge that the top two bits are the same.

We can look into improving that later. For now, it's fine to commit the patch with optimality checking removed.

changkhothuychung · 2024-05-18T22:05:37Z

looks like the BinaryExhaustive test fails when I remove the bool flag to enable Optimal check?

Oh, I thought this implementation was supposed to be optimal, but maybe I got that wrong.

Patch LGTM anyway.

I am assuming I need to put back the flag to disable optimality check ?

goldsteinn · 2024-05-19T00:48:01Z

looks like the BinaryExhaustive test fails when I remove the bool flag to enable Optimal check?

Oh, I thought this implementation was supposed to be optimal, but maybe I got that wrong.
Patch LGTM anyway.

I am assuming I need to put back the flag to disable optimality check ?

You already do. Its the bool argument.

jayfoad · 2024-05-19T07:31:14Z

looks like the BinaryExhaustive test fails when I remove the bool flag to enable Optimal check?

Oh, I thought this implementation was supposed to be optimal, but maybe I got that wrong.

Patch LGTM anyway.

I am assuming I need to put back the flag to disable optimality check ?

Yes (at least for the signed functions CeilS and FloorS) because you can't commit with failing tests.

RKSimon

LGTM

changkhothuychung · 2024-05-19T13:49:50Z

looks like the BinaryExhaustive test fails when I remove the bool flag to enable Optimal check?

Oh, I thought this implementation was supposed to be optimal, but maybe I got that wrong.
Patch LGTM anyway.

I am assuming I need to put back the flag to disable optimality check ?

You already do. Its the bool argument.

I made a push to put it back after I made that comment.

changkhothuychung · 2024-05-19T13:50:25Z

Thanks everyon! looks like I got 2 approves already, I will merge this PR shortly if there is no other concern.

changkhothuychung · 2024-05-19T20:12:23Z

@RKSimon RK
it looks like there is a failed build in later stages after the PR was merged - https://lab.llvm.org/buildbot/#/builders/185/builds/6813

Should we revert the changes?

RKSimon · 2024-05-19T20:32:42Z

wait until the current build has finished to see if it was an intermittent fail

initial attempt

e447f4c

llvmbot added the llvm:support label Mar 24, 2024

add definitions to header file

8b6e8bb

RKSimon requested review from jayfoad, RKSimon and goldsteinn April 1, 2024 09:48

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changkhothuychung added 2 commits April 4, 2024 18:09

Merge branch 'main' into knownbits_impl

f7eff4e

fix comments

b0d8100

llvmbot added the llvm:SelectionDAG SelectionDAGISel as well label Apr 5, 2024

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changkhothuychung added 2 commits April 4, 2024 21:19

add tests

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remove opcode check

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fix test

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fix or operation

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fix variable name

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changkhothuychung added 4 commits May 17, 2024 00:01

syntax fix

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syntax fix

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syntax fix

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some fix

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changkhothuychung added 3 commits May 17, 2024 09:02

some fix

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revert

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make test optimal

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add avgCeilU back

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changkhothuychung added 2 commits May 17, 2024 12:03

remove spurious reformat

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remove spurious reformat

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jayfoad approved these changes May 17, 2024

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disable optimality check

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RKSimon approved these changes May 19, 2024

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changkhothuychung merged commit eab92cb into llvm:main May 19, 2024
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PeddleSpam mentioned this pull request May 20, 2024

[AMDGPU] Fix error in #88512. #92770

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RKSimon mentioned this pull request May 20, 2024

[Support] Add KnownBits implementations for avgFloor and avgCeil #84640

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[llvm] Add KnownBits implementations for avgFloor and avgCeil #86445

[llvm] Add KnownBits implementations for avgFloor and avgCeil #86445

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[llvm] Add KnownBits implementations for avgFloor and avgCeil #86445

[llvm] Add KnownBits implementations for avgFloor and avgCeil #86445

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