[RFC] re-enable GVNHoist by default

[labrinea]

Summary

My initial motivation for this came from https://reviews.llvm.org/D48122, where it was pointed out that my change didn't fit well in SimplifyCFG and therefore using GVNHoist was a better way to go. GVNHoist has been disabled for a while as there was a list of bugs related to it.

I have fixed the following bugs:

• https://bugs.llvm.org/show_bug.cgi?id=37808 -> https://reviews.llvm.org/D48372 (rL337149)
• https://bugs.llvm.org/show_bug.cgi?id=36787 -> https://reviews.llvm.org/D49555 (rL337674)
• https://bugs.llvm.org/show_bug.cgi?id=37445 -> https://reviews.llvm.org/D49425 (rL337680)

The next two bugs no longer occur, and it's unclear which commit fixed them:

• https://bugs.llvm.org/show_bug.cgi?id=36635
• https://bugs.llvm.org/show_bug.cgi?id=37791

I investigated this one and proved to be unrelated to GVNHoist, but a genuine bug in NewGvn:

• https://bugs.llvm.org/show_bug.cgi?id=37660

To convince myself GVNHoist is in a good state I made a successful bootstrap build of LLVM followed by check-all.

[xbolva00]

Did you test it with some benchmarks? Results?

If no miscompiles and results are generally good, this should be enabled again (just in time for 7.0?). Successful bootstrap is a good sign.

What about that bug in newgvn? You wrote a detailed description of it, possible to fix it easily or it needs time?

[sebpop]

Looks good to me.
Thanks Alexandros for fixing the last known bugs with gvn-hoist.

As Eli mentioned in https://reviews.llvm.org/D48122 the code of gvn-hoist has been used and tested quite extensively in the past year or two.
The initial implementation has been tested with llvm bootstrap, spec 2000, spec 2006, and several mobile proprietary benchmarks.

[xbolva00]

If so, LG too

[labrinea]

Did you test it with some benchmarks? Results?

I am running lnt, spec2000 and spec2006 on AArch64 at the moment. I'll post results soon.

What about that bug in newgvn? You wrote a detailed description of it, possible to fix it easily or it needs time?

I am not familiar with newgvn, therefore a fix will take time. Also it's out of the scope of this patch.

[xbolva00]

Since it is accepted, please merge it before Aug 1 (LLVM 7 branch time) :)

[xbolva00]

Bot reports failure
https://reviews.llvm.org/rL338297

[labrinea]

This got reverted because of an out-of-memory error on an ubsan buildbot. Details and fix here -> https://reviews.llvm.org/D50323. I'll update the tests upon rebase.

[labrinea]

Rebase rL338240 since the excessive memory usage observed when using GVNHoist with UBSan has been fixed by rL340818 (https://reviews.llvm.org/D50323).

[lebedev.ri]

lib/Passes/PassBuilder.cpp

182

Unrelated to this patch, but this desc is the same as for the previous option.
I suspect this should read "Enable the GVN sinking pass for the new PM (default = off)"

[efriedma]

LGTM

[xbolva00]

Please check https://bugs.llvm.org/show_bug.cgi?id=38807

[hiraditya]

https://bugs.llvm.org/show_bug.cgi?id=38807 has been fixed.

lib/Passes/PassBuilder.cpp

RunNewGVN("enable-npm-newgvn", cl::init(false),
               cl::Hidden, cl::ZeroOrMore,
               cl::desc("Run NewGVN instead of GVN"));
 
 static cl::opt<bool> EnableEarlyCSEMemSSA(
     "enable-npm-earlycse-memssa", cl::init(true), cl::Hidden,
     cl::desc("Enable the EarlyCSE w/ MemorySSA pass for the new PM (default = on)"));
 
 static cl::opt<bool> EnableGVNHoist(
-    "enable-npm-gvn-hoist", cl::init(false), cl::Hidden,
-    cl::desc("Enable the GVN hoisting pass for the new PM (default = off)"));
+    "enable-npm-gvn-hoist", cl::init(true), cl::Hidden,
+    cl::desc("Enable the GVN hoisting pass for the new PM (default = on)"));
 
 static cl::opt<bool> EnableGVNSink(
     "enable-npm-gvn-sink", cl::init(false), cl::Hidden,
     cl::desc("Enable the GVN hoisting pass for the new PM (default = off)"));
 
 static cl::opt<bool> EnableUnrollAndJam(
     "enable-npm-unroll-and-jam", cl::init(false), cl::Hidden,
     cl::desc("Enable the Unroll and Jam pass for the new PM (default = off)"));
 
 static cl::opt<bool> EnableSyntheticCounts(
     "enable-npm-synthetic-counts", cl::init(false), cl::Hidden, cl::ZeroOrMore,
     cl::desc("Run synthetic function entry count generation "

lib/Transforms/IPO/PassManagerBuilder.cpp

static cl::opt<int> PreInlineThreshold(
     cl::desc("Control the amount of inlining in pre-instrumentation inliner "
              "(default = 75)"));
 
 static cl::opt<bool> EnableEarlyCSEMemSSA(
     "enable-earlycse-memssa", cl::init(true), cl::Hidden,
     cl::desc("Enable the EarlyCSE w/ MemorySSA pass (default = on)"));
 
 static cl::opt<bool> EnableGVNHoist(
-    "enable-gvn-hoist", cl::init(false), cl::Hidden,
-    cl::desc("Enable the GVN hoisting pass (default = off)"));
+    "enable-gvn-hoist", cl::init(true), cl::Hidden,
+    cl::desc("Enable the GVN hoisting pass (default = on)"));
 
 static cl::opt<bool>
     DisableLibCallsShrinkWrap("disable-libcalls-shrinkwrap", cl::init(false),
                               cl::Hidden,
                               cl::desc("Disable shrink-wrap library calls"));
 
 static cl::opt<bool> EnableSimpleLoopUnswitch(
     "enable-simple-loop-unswitch", cl::init(false), cl::Hidden,

test/Other/new-pm-defaults.ll

 ; CHECK-O-NEXT: Running analysis: FunctionAnalysisManagerCGSCCProxy
 ; CHECK-O-NEXT: Running pass: PostOrderFunctionAttrsPass
 ; CHECK-O3-NEXT: Running pass: ArgumentPromotionPass
 ; CHECK-O-NEXT: Running pass: CGSCCToFunctionPassAdaptor<{{.*}}PassManager{{.*}}>
 ; CHECK-O-NEXT: Starting llvm::Function pass manager run.
 ; CHECK-O-NEXT: Running pass: SROA
 ; CHECK-O-NEXT: Running pass: EarlyCSEPass
 ; CHECK-O-NEXT: Running analysis: MemorySSAAnalysis
+; CHECK-O-NEXT: Running pass: GVNHoistPass on foo
+; CHECK-O-NEXT: Running analysis: PostDominatorTreeAnalysis on foo
+; CHECK-O-NEXT: Running analysis: MemoryDependenceAnalysis on foo
+; CHECK-O-NEXT: Running analysis: PhiValuesAnalysis on foo
 ; CHECK-O-NEXT: Running pass: SpeculativeExecutionPass
 ; CHECK-O-NEXT: Running pass: JumpThreadingPass
 ; CHECK-O-NEXT: Running analysis: LazyValueAnalysis
 ; CHECK-O-NEXT: Running pass: CorrelatedValuePropagationPass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O3-NEXT: AggressiveInstCombinePass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O1-NEXT: Running pass: LibCallsShrinkWrapPass

 ; CHECK-O-NEXT: Running pass: LoopIdiomRecognizePass
 ; CHECK-EP-LOOP-LATE-NEXT: Running pass: NoOpLoopPass
 ; CHECK-O-NEXT: Running pass: LoopDeletionPass
 ; CHECK-O-NEXT: Running pass: LoopFullUnrollPass
 ; CHECK-EP-LOOP-END-NEXT: Running pass: NoOpLoopPass
 ; CHECK-O-NEXT: Finished Loop pass manager run.
 ; CHECK-Os-NEXT: Running pass: MergedLoadStoreMotionPass
 ; CHECK-Os-NEXT: Running pass: GVN
-; CHECK-Os-NEXT: Running analysis: MemoryDependenceAnalysis
-; CHECK-Os-NEXT: Running analysis: PhiValuesAnalysis
 ; CHECK-Oz-NEXT: Running pass: MergedLoadStoreMotionPass
 ; CHECK-Oz-NEXT: Running pass: GVN
-; CHECK-Oz-NEXT: Running analysis: MemoryDependenceAnalysis
-; CHECK-Oz-NEXT: Running analysis: PhiValuesAnalysis
 ; CHECK-O2-NEXT: Running pass: MergedLoadStoreMotionPass
 ; CHECK-O2-NEXT: Running pass: GVN
-; CHECK-O2-NEXT: Running analysis: MemoryDependenceAnalysis
-; CHECK-O2-NEXT: Running analysis: PhiValuesAnalysis
 ; CHECK-O3-NEXT: Running pass: MergedLoadStoreMotionPass
 ; CHECK-O3-NEXT: Running pass: GVN
-; CHECK-O3-NEXT: Running analysis: MemoryDependenceAnalysis
-; CHECK-O3-NEXT: Running analysis: PhiValuesAnalysis
 ; CHECK-O-NEXT: Running pass: MemCpyOptPass
-; CHECK-O1-NEXT: Running analysis: MemoryDependenceAnalysis
-; CHECK-O1-NEXT: Running analysis: PhiValuesAnalysis
 ; CHECK-O-NEXT: Running pass: SCCPPass
 ; CHECK-O-NEXT: Running pass: BDCEPass
 ; CHECK-O-NEXT: Running analysis: DemandedBitsAnalysis
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-EP-PEEPHOLE-NEXT: Running pass: NoOpFunctionPass
 ; CHECK-O-NEXT: Running pass: JumpThreadingPass
 ; CHECK-O-NEXT: Running pass: CorrelatedValuePropagationPass
 ; CHECK-O-NEXT: Running pass: DSEPass
 ; CHECK-O-NEXT: Running pass: FunctionToLoopPassAdaptor<{{.*}}LICMPass{{.*}}>
 ; CHECK-O-NEXT: Starting llvm::Function pass manager run.
 ; CHECK-O-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O-NEXT: Running pass: LCSSAPass
 ; CHECK-O-NEXT: Finished llvm::Function pass manager run.
 ; CHECK-EP-SCALAR-LATE-NEXT: Running pass: NoOpFunctionPass
 ; CHECK-O-NEXT: Running pass: ADCEPass
-; CHECK-O-NEXT: Running analysis: PostDominatorTreeAnalysis
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-EP-PEEPHOLE-NEXT: Running pass: NoOpFunctionPass
 ; CHECK-O-NEXT: Finished llvm::Function pass manager run.
 ; CHECK-EP-CGSCC-LATE-NEXT: Running pass: NoOpCGSCCPass
 ; CHECK-O-NEXT: Finished CGSCC pass manager run.
 ; CHECK-O-NEXT: Finished llvm::Module pass manager run.
 ; CHECK-O-NEXT: Running pass: PassManager<{{.*}}Module{{.*}}>

test/Other/new-pm-thinlto-defaults.ll

 ; CHECK-O-NEXT: Running analysis: FunctionAnalysisManagerCGSCCProxy
 ; CHECK-O-NEXT: Running pass: PostOrderFunctionAttrsPass
 ; CHECK-O3-NEXT: Running pass: ArgumentPromotionPass
 ; CHECK-O-NEXT: Running pass: CGSCCToFunctionPassAdaptor<{{.*}}PassManager{{.*}}>
 ; CHECK-O-NEXT: Starting llvm::Function pass manager run.
 ; CHECK-O-NEXT: Running pass: SROA
 ; CHECK-O-NEXT: Running pass: EarlyCSEPass
 ; CHECK-O-NEXT: Running analysis: MemorySSAAnalysis
+; CHECK-O-NEXT: Running pass: GVNHoistPass on foo
+; CHECK-O-NEXT: Running analysis: PostDominatorTreeAnalysis on foo
+; CHECK-O-NEXT: Running analysis: MemoryDependenceAnalysis on foo
+; CHECK-O-NEXT: Running analysis: PhiValuesAnalysis on foo
 ; CHECK-O-NEXT: Running pass: SpeculativeExecutionPass
 ; CHECK-O-NEXT: Running pass: JumpThreadingPass
 ; CHECK-O-NEXT: Running analysis: LazyValueAnalysis
 ; CHECK-O-NEXT: Running pass: CorrelatedValuePropagationPass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O3-NEXT: Running pass: AggressiveInstCombinePass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O1-NEXT: Running pass: LibCallsShrinkWrapPass

 ; CHECK-O-NEXT: Starting Loop pass manager run.
 ; CHECK-O-NEXT: Running pass: IndVarSimplifyPass
 ; CHECK-O-NEXT: Running pass: LoopIdiomRecognizePass
 ; CHECK-O-NEXT: Running pass: LoopDeletionPass
 ; CHECK-O-NEXT: Running pass: LoopFullUnrollPass
 ; CHECK-O-NEXT: Finished Loop pass manager run.
 ; CHECK-Os-NEXT: Running pass: MergedLoadStoreMotionPass
 ; CHECK-Os-NEXT: Running pass: GVN
-; CHECK-Os-NEXT: Running analysis: MemoryDependenceAnalysis
-; CHECK-Os-NEXT: Running analysis: PhiValuesAnalysis
 ; CHECK-Oz-NEXT: Running pass: MergedLoadStoreMotionPass
 ; CHECK-Oz-NEXT: Running pass: GVN
-; CHECK-Oz-NEXT: Running analysis: MemoryDependenceAnalysis
-; CHECK-Oz-NEXT: Running analysis: PhiValuesAnalysis
 ; CHECK-O2-NEXT: Running pass: MergedLoadStoreMotionPass
 ; CHECK-O2-NEXT: Running pass: GVN
-; CHECK-O2-NEXT: Running analysis: MemoryDependenceAnalysis
-; CHECK-O2-NEXT: Running analysis: PhiValuesAnalysis
 ; CHECK-O3-NEXT: Running pass: MergedLoadStoreMotionPass
 ; CHECK-O3-NEXT: Running pass: GVN
-; CHECK-O3-NEXT: Running analysis: MemoryDependenceAnalysis
-; CHECK-O3-NEXT: Running analysis: PhiValuesAnalysis
 ; CHECK-O-NEXT: Running pass: MemCpyOptPass
-; CHECK-O1-NEXT: Running analysis: MemoryDependenceAnalysis
-; CHECK-O1-NEXT: Running analysis: PhiValuesAnalysis
 ; CHECK-O-NEXT: Running pass: SCCPPass
 ; CHECK-O-NEXT: Running pass: BDCEPass
 ; CHECK-O-NEXT: Running analysis: DemandedBitsAnalysis
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Running pass: JumpThreadingPass
 ; CHECK-O-NEXT: Running pass: CorrelatedValuePropagationPass
 ; CHECK-O-NEXT: Running pass: DSEPass
 ; CHECK-O-NEXT: Running pass: FunctionToLoopPassAdaptor<{{.*}}LICMPass{{.*}}>
 ; CHECK-O-NEXT: Starting llvm::Function pass manager run
 ; CHECK-O-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O-NEXT: Running pass: LCSSAPass
 ; CHECK-O-NEXT: Finished llvm::Function pass manager run
 ; CHECK-O-NEXT: Running pass: ADCEPass
-; CHECK-O-NEXT: Running analysis: PostDominatorTreeAnalysis
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Finished llvm::Function pass manager run.
 ; CHECK-O-NEXT: Finished CGSCC pass manager run.
 ; CHECK-O-NEXT: Finished llvm::Module pass manager run.
 ; CHECK-PRELINK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-POSTLINK-O-NEXT: Running pass: PassManager<{{.*}}Module{{.*}}>
 ; CHECK-POSTLINK-O-NEXT: Starting llvm::Module pass manager run.

test/Other/opt-O2-pipeline.ll

 ; CHECK-NEXT:       Deduce function attributes
 ; CHECK-NEXT:       FunctionPass Manager
 ; CHECK-NEXT:         Dominator Tree Construction
 ; CHECK-NEXT:         SROA
 ; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
 ; CHECK-NEXT:         Function Alias Analysis Results
 ; CHECK-NEXT:         Memory SSA
 ; CHECK-NEXT:         Early CSE w/ MemorySSA
+; CHECK-NEXT:         Post-Dominator Tree Construction
+; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:         Function Alias Analysis Results
+; CHECK-NEXT:         Phi Values Analysis
+; CHECK-NEXT:         Memory Dependence Analysis
+; CHECK-NEXT:         Early GVN Hoisting of Expressions
 ; CHECK-NEXT:         Speculatively execute instructions if target has divergent branches
 ; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
 ; CHECK-NEXT:         Function Alias Analysis Results
 ; CHECK-NEXT:         Lazy Value Information Analysis
 ; CHECK-NEXT:         Jump Threading
 ; CHECK-NEXT:         Value Propagation
 ; CHECK-NEXT:         Simplify the CFG
 ; CHECK-NEXT:         Dominator Tree Construction

test/Other/opt-O3-pipeline.ll

 ; CHECK-NEXT:       Promote 'by reference' arguments to scalars
 ; CHECK-NEXT:       FunctionPass Manager
 ; CHECK-NEXT:         Dominator Tree Construction
 ; CHECK-NEXT:         SROA
 ; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
 ; CHECK-NEXT:         Function Alias Analysis Results
 ; CHECK-NEXT:         Memory SSA
 ; CHECK-NEXT:         Early CSE w/ MemorySSA
+; CHECK-NEXT:         Post-Dominator Tree Construction
+; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:         Function Alias Analysis Results
+; CHECK-NEXT:         Phi Values Analysis
+; CHECK-NEXT:         Memory Dependence Analysis
+; CHECK-NEXT:         Early GVN Hoisting of Expressions
 ; CHECK-NEXT:         Speculatively execute instructions if target has divergent branches
 ; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
 ; CHECK-NEXT:         Function Alias Analysis Results
 ; CHECK-NEXT:         Lazy Value Information Analysis
 ; CHECK-NEXT:         Jump Threading
 ; CHECK-NEXT:         Value Propagation
 ; CHECK-NEXT:         Simplify the CFG
 ; CHECK-NEXT:         Dominator Tree Construction

test/Other/opt-Os-pipeline.ll

 ; CHECK-NEXT:       Deduce function attributes
 ; CHECK-NEXT:       FunctionPass Manager
 ; CHECK-NEXT:         Dominator Tree Construction
 ; CHECK-NEXT:         SROA
 ; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
 ; CHECK-NEXT:         Function Alias Analysis Results
 ; CHECK-NEXT:         Memory SSA
 ; CHECK-NEXT:         Early CSE w/ MemorySSA
+; CHECK-NEXT:         Post-Dominator Tree Construction
+; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:         Function Alias Analysis Results
+; CHECK-NEXT:         Phi Values Analysis
+; CHECK-NEXT:         Memory Dependence Analysis
+; CHECK-NEXT:         Early GVN Hoisting of Expressions
 ; CHECK-NEXT:         Speculatively execute instructions if target has divergent branches
 ; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
 ; CHECK-NEXT:         Function Alias Analysis Results
 ; CHECK-NEXT:         Lazy Value Information Analysis
 ; CHECK-NEXT:         Jump Threading
 ; CHECK-NEXT:         Value Propagation
 ; CHECK-NEXT:         Simplify the CFG
 ; CHECK-NEXT:         Dominator Tree Construction