Enable EliminateAvailableExternally pass for -O1

[vlad.tsyrklevich]

Summary

Follow-up to D43690, the EliminateAvailableExternally pass currently
runs under -O0 and -O2 and up. Under -O1 we would still want to drop
available_externally symbols to reduce space without inlining having
run.

[vlad.tsyrklevich]

test/Other/opt-O1-pipeline.ll

166

Highlighting the relevant portion of this test.

[tejohnson]

LGTM

I just checked the new PM and it does seem to run this already at O1 (at least, by visual inspection of the code it appears to). OTOH the new PM doesn't appear to run any opt passes at -O0, so that's a bit different than what is happening in the old PM, but that is a separate issue.

lib/Transforms/IPO/PassManagerBuilder.cpp

void PassManagerBuilder::populateModulePassManager(
   // FIXME: This is a HACK! The inliner pass above implicitly creates a CGSCC
   // pass manager that we are specifically trying to avoid. To prevent this
   // we must insert a no-op module pass to reset the pass manager.
   MPM.add(createBarrierNoopPass());
 
   if (RunPartialInlining)
     MPM.add(createPartialInliningPass());
 
-  if (OptLevel > 1 && !PrepareForLTO && !PrepareForThinLTO)
+  if (!PrepareForLTO && !PrepareForThinLTO)
     // Remove avail extern fns and globals definitions if we aren't
     // compiling an object file for later LTO. For LTO we want to preserve
     // these so they are eligible for inlining at link-time. Note if they
     // are unreferenced they will be removed by GlobalDCE later, so
     // this only impacts referenced available externally globals.
     // Eventually they will be suppressed during codegen, but eliminating
     // here enables more opportunity for GlobalDCE as it may make
     // globals referenced by available external functions dead

test/Other/opt-O1-pipeline.ll

+; RUN: opt -mtriple=x86_64-- -O1 -debug-pass=Structure < %s -o /dev/null 2>&1 | FileCheck %s
+
+; REQUIRES: asserts
+
+; CHECK-LABEL: Pass Arguments:
+; CHECK-NEXT: Target Transform Information
+; CHECK-NEXT: Type-Based Alias Analysis
+; CHECK-NEXT: Scoped NoAlias Alias Analysis
+; CHECK-NEXT: Assumption Cache Tracker
+; CHECK-NEXT: Target Library Information
+; CHECK-NEXT:   FunctionPass Manager
+; CHECK-NEXT:     Module Verifier
+; CHECK-NEXT:     Instrument function entry/exit with calls to e.g. mcount() (pre inlining)
+; CHECK-NEXT:     Simplify the CFG
+; CHECK-NEXT:     Dominator Tree Construction
+; CHECK-NEXT:     SROA
+; CHECK-NEXT:     Early CSE
+; CHECK-NEXT:     Lower 'expect' Intrinsics
+; CHECK-NEXT: Pass Arguments:
+; CHECK-NEXT: Target Library Information
+; CHECK-NEXT: Target Transform Information
+;             Target Pass Configuration
+; CHECK:      Type-Based Alias Analysis
+; CHECK-NEXT: Scoped NoAlias Alias Analysis
+; CHECK-NEXT: Assumption Cache Tracker
+; CHECK-NEXT: Profile summary info
+; CHECK-NEXT:   ModulePass Manager
+; CHECK-NEXT:     Force set function attributes
+; CHECK-NEXT:     Infer set function attributes
+; CHECK-NEXT:     Interprocedural Sparse Conditional Constant Propagation
+; CHECK-NEXT:     Called Value Propagation
+; CHECK-NEXT:     Global Variable Optimizer
+; CHECK-NEXT:       Unnamed pass: implement Pass::getPassName()
+; CHECK-NEXT:     FunctionPass Manager
+; CHECK-NEXT:       Dominator Tree Construction
+; CHECK-NEXT:       Promote Memory to Register
+; CHECK-NEXT:     Dead Argument Elimination
+; CHECK-NEXT:     FunctionPass Manager
+; CHECK-NEXT:       Dominator Tree Construction
+; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:       Function Alias Analysis Results
+; CHECK-NEXT:       Natural Loop Information
+; CHECK-NEXT:       Lazy Branch Probability Analysis
+; CHECK-NEXT:       Lazy Block Frequency Analysis
+; CHECK-NEXT:       Optimization Remark Emitter
+; CHECK-NEXT:       Combine redundant instructions
+; CHECK-NEXT:       Simplify the CFG
+; CHECK-NEXT:     CallGraph Construction
+; CHECK-NEXT:     Globals Alias Analysis
+; CHECK-NEXT:     Call Graph SCC Pass Manager
+; CHECK-NEXT:       Remove unused exception handling info
+; CHECK-NEXT:       Inliner for always_inline functions
+; 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:         Speculatively execute instructions if target has divergent branches
+; CHECK-NEXT:         Dominator Tree Construction
+; 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
+; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:         Function Alias Analysis Results
+; CHECK-NEXT:         Natural Loop Information
+; CHECK-NEXT:         Lazy Branch Probability Analysis
+; CHECK-NEXT:         Lazy Block Frequency Analysis
+; CHECK-NEXT:         Optimization Remark Emitter
+; CHECK-NEXT:         Combine redundant instructions
+; CHECK-NEXT:         Conditionally eliminate dead library calls
+; CHECK-NEXT:         Natural Loop Information
+; CHECK-NEXT:         Branch Probability Analysis
+; CHECK-NEXT:         Block Frequency Analysis
+; CHECK-NEXT:         Lazy Branch Probability Analysis
+; CHECK-NEXT:         Lazy Block Frequency Analysis
+; CHECK-NEXT:         Optimization Remark Emitter
+; CHECK-NEXT:         PGOMemOPSize
+; CHECK-NEXT:         Dominator Tree Construction
+; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:         Function Alias Analysis Results
+; CHECK-NEXT:         Natural Loop Information
+; CHECK-NEXT:         Lazy Branch Probability Analysis
+; CHECK-NEXT:         Lazy Block Frequency Analysis
+; CHECK-NEXT:         Optimization Remark Emitter
+; CHECK-NEXT:         Tail Call Elimination
+; CHECK-NEXT:         Simplify the CFG
+; CHECK-NEXT:         Reassociate expressions
+; CHECK-NEXT:         Dominator Tree Construction
+; CHECK-NEXT:         Natural Loop Information
+; CHECK-NEXT:         Canonicalize natural loops
+; CHECK-NEXT:         LCSSA Verifier
+; CHECK-NEXT:         Loop-Closed SSA Form Pass
+; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:         Function Alias Analysis Results
+; CHECK-NEXT:         Scalar Evolution Analysis
+; CHECK-NEXT:         Loop Pass Manager
+; CHECK-NEXT:           Rotate Loops
+; CHECK-NEXT:           Loop Invariant Code Motion
+; CHECK-NEXT:           Unswitch loops
+; CHECK-NEXT:         Simplify the CFG
+; CHECK-NEXT:         Dominator Tree Construction
+; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:         Function Alias Analysis Results
+; CHECK-NEXT:         Natural Loop Information
+; CHECK-NEXT:         Lazy Branch Probability Analysis
+; CHECK-NEXT:         Lazy Block Frequency Analysis
+; CHECK-NEXT:         Optimization Remark Emitter
+; CHECK-NEXT:         Combine redundant instructions
+; CHECK-NEXT:         Canonicalize natural loops
+; CHECK-NEXT:         LCSSA Verifier
+; CHECK-NEXT:         Loop-Closed SSA Form Pass
+; CHECK-NEXT:         Scalar Evolution Analysis
+; CHECK-NEXT:         Loop Pass Manager
+; CHECK-NEXT:           Induction Variable Simplification
+; CHECK-NEXT:           Recognize loop idioms
+; CHECK-NEXT:           Delete dead loops
+; CHECK-NEXT:           Unroll loops
+; CHECK-NEXT:         Memory Dependence Analysis
+; CHECK-NEXT:         MemCpy Optimization
+; CHECK-NEXT:         Sparse Conditional Constant Propagation
+; CHECK-NEXT:         Dominator Tree Construction
+; CHECK-NEXT:         Demanded bits analysis
+; CHECK-NEXT:         Bit-Tracking Dead Code Elimination
+; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:         Function Alias Analysis Results
+; CHECK-NEXT:         Natural Loop Information
+; CHECK-NEXT:         Lazy Branch Probability Analysis
+; CHECK-NEXT:         Lazy Block Frequency Analysis
+; CHECK-NEXT:         Optimization Remark Emitter
+; CHECK-NEXT:         Combine redundant instructions
+; CHECK-NEXT:         Lazy Value Information Analysis
+; CHECK-NEXT:         Jump Threading
+; CHECK-NEXT:         Value Propagation
+; CHECK-NEXT:         Dominator Tree Construction
+; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:         Function Alias Analysis Results
+; CHECK-NEXT:         Memory Dependence Analysis
+; CHECK-NEXT:         Dead Store Elimination
+; CHECK-NEXT:         Natural Loop Information
+; CHECK-NEXT:         Canonicalize natural loops
+; CHECK-NEXT:         LCSSA Verifier
+; CHECK-NEXT:         Loop-Closed SSA Form Pass
+; CHECK-NEXT:         Function Alias Analysis Results
+; CHECK-NEXT:         Scalar Evolution Analysis
+; CHECK-NEXT:         Loop Pass Manager
+; CHECK-NEXT:           Loop Invariant Code Motion
+; CHECK-NEXT:         Post-Dominator Tree Construction
+; CHECK-NEXT:         Aggressive Dead Code Elimination
+; CHECK-NEXT:         Simplify the CFG
+; CHECK-NEXT:         Dominator Tree Construction
+; CHECK-NEXT:         Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:         Function Alias Analysis Results
+; CHECK-NEXT:         Natural Loop Information
+; CHECK-NEXT:         Lazy Branch Probability Analysis
+; CHECK-NEXT:         Lazy Block Frequency Analysis
+; CHECK-NEXT:         Optimization Remark Emitter
+; CHECK-NEXT:         Combine redundant instructions
+; CHECK-NEXT:     A No-Op Barrier Pass
+; CHECK-NEXT:     Eliminate Available Externally Globals
+; CHECK-NEXT:     CallGraph Construction
+; CHECK-NEXT:     Deduce function attributes in RPO
+; CHECK-NEXT:     Global Variable Optimizer
+; CHECK-NEXT:       Unnamed pass: implement Pass::getPassName()
+; CHECK-NEXT:     Dead Global Elimination
+; CHECK-NEXT:     CallGraph Construction
+; CHECK-NEXT:     Globals Alias Analysis
+; CHECK-NEXT:     FunctionPass Manager
+; CHECK-NEXT:       Float to int
+; CHECK-NEXT:       Dominator Tree Construction
+; CHECK-NEXT:       Natural Loop Information
+; CHECK-NEXT:       Canonicalize natural loops
+; CHECK-NEXT:       LCSSA Verifier
+; CHECK-NEXT:       Loop-Closed SSA Form Pass
+; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:       Function Alias Analysis Results
+; CHECK-NEXT:       Scalar Evolution Analysis
+; CHECK-NEXT:       Loop Pass Manager
+; CHECK-NEXT:         Rotate Loops
+; CHECK-NEXT:       Loop Access Analysis
+; CHECK-NEXT:       Lazy Branch Probability Analysis
+; CHECK-NEXT:       Lazy Block Frequency Analysis
+; CHECK-NEXT:       Optimization Remark Emitter
+; CHECK-NEXT:       Loop Distribution
+; CHECK-NEXT:       Branch Probability Analysis
+; CHECK-NEXT:       Block Frequency Analysis
+; CHECK-NEXT:       Scalar Evolution Analysis
+; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:       Function Alias Analysis Results
+; CHECK-NEXT:       Loop Access Analysis
+; CHECK-NEXT:       Demanded bits analysis
+; CHECK-NEXT:       Lazy Branch Probability Analysis
+; CHECK-NEXT:       Lazy Block Frequency Analysis
+; CHECK-NEXT:       Optimization Remark Emitter
+; CHECK-NEXT:       Loop Vectorization
+; CHECK-NEXT:       Canonicalize natural loops
+; CHECK-NEXT:       Scalar Evolution Analysis
+; CHECK-NEXT:       Function Alias Analysis Results
+; CHECK-NEXT:       Loop Access Analysis
+; CHECK-NEXT:       Loop Load Elimination
+; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:       Function Alias Analysis Results
+; CHECK-NEXT:       Lazy Branch Probability Analysis
+; CHECK-NEXT:       Lazy Block Frequency Analysis
+; CHECK-NEXT:       Optimization Remark Emitter
+; CHECK-NEXT:       Combine redundant instructions
+; CHECK-NEXT:       Simplify the CFG
+; CHECK-NEXT:       Dominator Tree Construction
+; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:       Function Alias Analysis Results
+; CHECK-NEXT:       Natural Loop Information
+; CHECK-NEXT:       Lazy Branch Probability Analysis
+; CHECK-NEXT:       Lazy Block Frequency Analysis
+; CHECK-NEXT:       Optimization Remark Emitter
+; CHECK-NEXT:       Combine redundant instructions
+; CHECK-NEXT:       Canonicalize natural loops
+; CHECK-NEXT:       LCSSA Verifier
+; CHECK-NEXT:       Loop-Closed SSA Form Pass
+; CHECK-NEXT:       Scalar Evolution Analysis
+; CHECK-NEXT:       Loop Pass Manager
+; CHECK-NEXT:         Unroll loops
+; CHECK-NEXT:       Lazy Branch Probability Analysis
+; CHECK-NEXT:       Lazy Block Frequency Analysis
+; CHECK-NEXT:       Optimization Remark Emitter
+; CHECK-NEXT:       Combine redundant instructions
+; CHECK-NEXT:       Canonicalize natural loops
+; CHECK-NEXT:       LCSSA Verifier
+; CHECK-NEXT:       Loop-Closed SSA Form Pass
+; CHECK-NEXT:       Scalar Evolution Analysis
+; CHECK-NEXT:       Loop Pass Manager
+; CHECK-NEXT:         Loop Invariant Code Motion
+; CHECK-NEXT:       Alignment from assumptions
+; CHECK-NEXT:     Strip Unused Function Prototypes
+; CHECK-NEXT:     FunctionPass Manager
+; CHECK-NEXT:       Dominator Tree Construction
+; CHECK-NEXT:       Natural Loop Information
+; CHECK-NEXT:       Branch Probability Analysis
+; CHECK-NEXT:       Block Frequency Analysis
+; CHECK-NEXT:       Canonicalize natural loops
+; CHECK-NEXT:       LCSSA Verifier
+; CHECK-NEXT:       Loop-Closed SSA Form Pass
+; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
+; CHECK-NEXT:       Function Alias Analysis Results
+; CHECK-NEXT:       Scalar Evolution Analysis
+; CHECK-NEXT:       Branch Probability Analysis
+; CHECK-NEXT:       Block Frequency Analysis
+; CHECK-NEXT:       Loop Pass Manager
+; CHECK-NEXT:         Loop Sink
+; CHECK-NEXT:       Lazy Branch Probability Analysis
+; CHECK-NEXT:       Lazy Block Frequency Analysis
+; CHECK-NEXT:       Optimization Remark Emitter
+; CHECK-NEXT:       Remove redundant instructions
+; CHECK-NEXT:       Hoist/decompose integer division and remainder
+; CHECK-NEXT:       Simplify the CFG
+; CHECK-NEXT:       Module Verifier
+; CHECK-NEXT:     Bitcode Writer
+; CHECK-NEXT: Pass Arguments:
+; CHECK-NEXT: Target Library Information
+; CHECK-NEXT:   FunctionPass Manager
+; CHECK-NEXT:     Dominator Tree Construction
+; CHECK-NEXT:     Natural Loop Information
+; CHECK-NEXT:     Branch Probability Analysis
+; CHECK-NEXT:     Block Frequency Analysis
+; CHECK-NEXT: Pass Arguments:
+; CHECK-NEXT: Target Library Information
+; CHECK-NEXT:   FunctionPass Manager
+; CHECK-NEXT:     Dominator Tree Construction
+; CHECK-NEXT:     Natural Loop Information
+; CHECK-NEXT:     Branch Probability Analysis
+; CHECK-NEXT:     Block Frequency Analysis
+
+define void @f() {
+  ret void
+}