[llvm] r356803 - Fix non-determinism in Reassociate caused by address coincidences
Daniel Sanders via llvm-commits
llvm-commits at lists.llvm.org
Fri Mar 22 13:16:35 PDT 2019
Author: dsanders
Date: Fri Mar 22 13:16:35 2019
New Revision: 356803
URL: http://llvm.org/viewvc/llvm-project?rev=356803&view=rev
Log:
Fix non-determinism in Reassociate caused by address coincidences
Summary:
Between building the pair map and querying it there are a few places that
erase and create Values. It's rare but the address of these newly created
Values is occasionally the same as a just-erased Value that we already
have in the pair map. These coincidences should be accounted for to avoid
non-determinism.
Thanks to Roman Tereshin for the test case.
Reviewers: rtereshin, bogner
Reviewed By: rtereshin
Subscribers: mgrang, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D59401
Added:
llvm/trunk/test/Transforms/Reassociate/pointer-collision-non-determinism.ll
Modified:
llvm/trunk/include/llvm/Transforms/Scalar/Reassociate.h
llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp
Modified: llvm/trunk/include/llvm/Transforms/Scalar/Reassociate.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Scalar/Reassociate.h?rev=356803&r1=356802&r2=356803&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Transforms/Scalar/Reassociate.h (original)
+++ llvm/trunk/include/llvm/Transforms/Scalar/Reassociate.h Fri Mar 22 13:16:35 2019
@@ -82,7 +82,14 @@ protected:
static const unsigned GlobalReassociateLimit = 10;
static const unsigned NumBinaryOps =
Instruction::BinaryOpsEnd - Instruction::BinaryOpsBegin;
- DenseMap<std::pair<Value *, Value *>, unsigned> PairMap[NumBinaryOps];
+
+ struct PairMapValue {
+ WeakVH Value1;
+ WeakVH Value2;
+ unsigned Score;
+ bool isValid() const { return Value1 && Value2; }
+ };
+ DenseMap<std::pair<Value *, Value *>, PairMapValue> PairMap[NumBinaryOps];
bool MadeChange;
Modified: llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp?rev=356803&r1=356802&r2=356803&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp Fri Mar 22 13:16:35 2019
@@ -2217,8 +2217,15 @@ void ReassociatePass::ReassociateExpress
if (std::less<Value *>()(Op1, Op0))
std::swap(Op0, Op1);
auto it = PairMap[Idx].find({Op0, Op1});
- if (it != PairMap[Idx].end())
- Score += it->second;
+ if (it != PairMap[Idx].end()) {
+ // Functions like BreakUpSubtract() can erase the Values we're using
+ // as keys and create new Values after we built the PairMap. There's a
+ // small chance that the new nodes can have the same address as
+ // something already in the table. We shouldn't accumulate the stored
+ // score in that case as it refers to the wrong Value.
+ if (it->second.isValid())
+ Score += it->second.Score;
+ }
unsigned MaxRank = std::max(Ops[i].Rank, Ops[j].Rank);
if (Score > Max || (Score == Max && MaxRank < BestRank)) {
@@ -2287,9 +2294,15 @@ ReassociatePass::BuildPairMap(ReversePos
std::swap(Op0, Op1);
if (!Visited.insert({Op0, Op1}).second)
continue;
- auto res = PairMap[BinaryIdx].insert({{Op0, Op1}, 1});
- if (!res.second)
- ++res.first->second;
+ auto res = PairMap[BinaryIdx].insert({{Op0, Op1}, {Op0, Op1, 1}});
+ if (!res.second) {
+ // If either key value has been erased then we've got the same
+ // address by coincidence. That can't happen here because nothing is
+ // erasing values but it can happen by the time we're querying the
+ // map.
+ assert(res.first->second.isValid() && "WeakVH invalidated");
+ ++res.first->second.Score;
+ }
}
}
}
Added: llvm/trunk/test/Transforms/Reassociate/pointer-collision-non-determinism.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/Reassociate/pointer-collision-non-determinism.ll?rev=356803&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/Reassociate/pointer-collision-non-determinism.ll (added)
+++ llvm/trunk/test/Transforms/Reassociate/pointer-collision-non-determinism.ll Fri Mar 22 13:16:35 2019
@@ -0,0 +1,107 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -run-twice -reassociate %s -S -o - | FileCheck %s
+; RUN: opt -run-twice -reassociate %s -S -o - | FileCheck %s
+
+; The PairMap[NumBinaryOps] used by the Reassociate pass used to have Value
+; *pointers as keys and no handling for values being removed. In some cases (in
+; practice very rarely, but in this particular test - well over 50% of the time)
+; a newly created Value would happen to get allocated at the same memory
+; address, effectively "replacing" the key in the map.
+;
+; Test that that doesn't happen anymore and the pass is deterministic.
+;
+; The failure rate of this test (at least, on my 8 core iMac), when ran in the
+; context of other unit tests executed | specifically, I was trying
+;
+; ./bin/llvm-lit -v ../test/Transforms/Reassociate
+;
+; is as follows:
+;
+; # of RUN lines repeated | just -run-twice | -run-twice and CHECK lines
+; ------------------------+-----------------+---------------------------
+; 1 | 30% | <didn't measure>
+; 2 | 55% | 95%
+; 3 | 55% | <didn't measure>
+;
+; hence the specific shape of this test. The IR itself comes from a real-world
+; code, successfully bugpointed.
+
+define float @test(float %arg) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[TMP:%.*]] = fmul fast float [[ARG:%.*]], 0x3FE99999A0000000
+; CHECK-NEXT: [[TMP110:%.*]] = fsub fast float 1.000000e+00, [[TMP]]
+; CHECK-NEXT: [[TMP2:%.*]] = fmul fast float [[ARG]], 0x3FE99999A0000000
+; CHECK-NEXT: [[TMP311:%.*]] = fsub fast float 1.000000e+00, [[TMP2]]
+; CHECK-NEXT: [[REASS_MUL160:%.*]] = fmul fast float [[TMP110]], [[ARG]]
+; CHECK-NEXT: [[TMP4:%.*]] = fmul fast float [[REASS_MUL160]], [[TMP311]]
+; CHECK-NEXT: [[TMP5:%.*]] = fadd fast float [[TMP4]], [[ARG]]
+; CHECK-NEXT: [[TMP6:%.*]] = fmul fast float [[TMP5]], [[ARG]]
+; CHECK-NEXT: [[TMP7:%.*]] = fadd fast float [[TMP6]], [[ARG]]
+; CHECK-NEXT: [[TMP8:%.*]] = fmul fast float [[TMP7]], [[ARG]]
+; CHECK-NEXT: [[TMP9:%.*]] = fadd fast float [[TMP8]], [[ARG]]
+; CHECK-NEXT: [[TMP10:%.*]] = fmul fast float [[TMP9]], [[ARG]]
+; CHECK-NEXT: [[TMP11:%.*]] = fadd fast float [[TMP10]], [[ARG]]
+; CHECK-NEXT: [[TMP12:%.*]] = fmul fast float [[TMP11]], [[ARG]]
+; CHECK-NEXT: [[TMP13:%.*]] = fadd fast float [[TMP12]], [[ARG]]
+; CHECK-NEXT: [[TMP14:%.*]] = fmul fast float [[TMP13]], [[ARG]]
+; CHECK-NEXT: [[TMP15:%.*]] = fadd fast float [[TMP14]], [[ARG]]
+; CHECK-NEXT: [[TMP16:%.*]] = fmul fast float [[TMP15]], [[ARG]]
+; CHECK-NEXT: [[TMP17:%.*]] = fadd fast float [[TMP16]], [[ARG]]
+; CHECK-NEXT: [[TMP18:%.*]] = fmul fast float [[TMP17]], [[ARG]]
+; CHECK-NEXT: [[TMP19:%.*]] = fadd fast float [[TMP18]], [[ARG]]
+; CHECK-NEXT: [[TMP20:%.*]] = fmul fast float [[TMP19]], [[ARG]]
+; CHECK-NEXT: [[TMP21:%.*]] = fadd fast float [[TMP20]], [[ARG]]
+; CHECK-NEXT: [[TMP22:%.*]] = fmul fast float [[TMP21]], [[ARG]]
+; CHECK-NEXT: [[TMP23:%.*]] = fadd fast float [[TMP22]], [[ARG]]
+; CHECK-NEXT: [[REASS_MUL166:%.*]] = fmul fast float [[ARG]], [[ARG]]
+; CHECK-NEXT: [[TMP24:%.*]] = fmul fast float [[REASS_MUL166]], [[TMP23]]
+; CHECK-NEXT: [[TMP25:%.*]] = fadd fast float [[TMP24]], [[ARG]]
+; CHECK-NEXT: [[TMP26:%.*]] = fmul fast float [[TMP25]], [[ARG]]
+; CHECK-NEXT: [[TMP27:%.*]] = fadd fast float [[TMP26]], [[ARG]]
+; CHECK-NEXT: [[TMP29:%.*]] = fmul fast float [[ARG]], [[ARG]]
+; CHECK-NEXT: [[TMP31:%.*]] = fmul fast float [[TMP29]], 0x3FEA2E8B80000000
+; CHECK-NEXT: [[TMP33:%.*]] = fmul fast float [[TMP31]], [[TMP27]]
+; CHECK-NEXT: [[TMP34:%.*]] = fadd fast float [[TMP33]], [[ARG]]
+; CHECK-NEXT: ret float [[TMP34]]
+;
+entry:
+ %tmp = fmul fast float %arg, 0xBFE99999A0000000
+ %tmp1 = fadd fast float %tmp, 1.000000e+00
+ %tmp2 = fmul fast float %arg, 0xBFE99999A0000000
+ %tmp3 = fadd fast float %tmp2, 1.000000e+00
+ %reass.mul156 = fmul fast float %arg, %tmp1
+ %reass.mul160 = fmul fast float %arg, %tmp1
+ %tmp4 = fmul fast float %reass.mul160, %tmp3
+ %tmp5 = fadd fast float %arg, %tmp4
+ %tmp6 = fmul fast float %tmp5, %arg
+ %tmp7 = fadd fast float %tmp6, %arg
+ %tmp8 = fmul fast float %tmp7, %arg
+ %tmp9 = fadd fast float %arg, %tmp8
+ %tmp10 = fmul fast float %tmp9, %arg
+ %tmp11 = fadd fast float %tmp10, %arg
+ %tmp12 = fmul fast float %tmp11, %arg
+ %tmp13 = fadd fast float %tmp12, %arg
+ %tmp14 = fmul fast float %tmp13, %arg
+ %tmp15 = fadd fast float %arg, %tmp14
+ %tmp16 = fmul fast float %tmp15, %arg
+ %tmp17 = fadd fast float %tmp16, %arg
+ %tmp18 = fmul fast float %tmp17, %arg
+ %tmp19 = fadd fast float %tmp18, %arg
+ %tmp20 = fmul fast float %tmp19, %arg
+ %tmp21 = fadd fast float %tmp20, %arg
+ %tmp22 = fmul fast float %tmp21, %arg
+ %tmp23 = fadd fast float %tmp22, %arg
+ %reass.mul166 = fmul fast float %arg, %tmp23
+ %tmp24 = fmul fast float %reass.mul166, %arg
+ %tmp25 = fadd fast float %arg, %tmp24
+ %tmp26 = fmul fast float %arg, %tmp25
+ %tmp27 = fadd fast float %tmp26, %arg
+ %tmp28 = fmul fast float %arg, %tmp27
+ %tmp29 = fmul fast float %tmp28, %arg
+ %tmp31 = fmul fast float %tmp29, 0x3FED1745C0000000
+ %tmp33 = fmul fast float %tmp31, 0x3FECCCCCC0000000
+ %tmp34 = fadd fast float %arg, %tmp33
+ ret float %tmp34
+}
+
More information about the llvm-commits
mailing list