perf: Only run final commit if adce_pass! made any intersting changes

adce_pass! runs its own compaction, so we only need to run another run
of compaction if it made any post-compaction changes.

Author: Keno

base/compiler/inferencestate.jl

@@ -205,7 +205,7 @@ const CACHE_MODE_VOLATILE = 0x01 << 2 # not cached, optimization allowed
 
 mutable struct TryCatchFrame
     exct
-    const enter_idx
+    const enter_idx::Int
     TryCatchFrame(@nospecialize(exct), enter_idx::Int) = new(exct, enter_idx)
 end
 

base/compiler/optimize.jl

@@ -925,8 +925,10 @@ function run_passes_ipo_safe(
     # @timeit "verify 2" verify_ir(ir)
     @pass "compact 2" ir = compact!(ir)
     @pass "SROA"      ir = sroa_pass!(ir, sv.inlining)
-    @pass "ADCE"      ir = adce_pass!(ir, sv.inlining)
-    @pass "compact 3" ir = compact!(ir, true)
+    @pass "ADCE"      (ir, made_changes) = adce_pass!(ir, sv.inlining)
+    if made_changes
+        @pass "compact 3" ir = compact!(ir, true)
+    end
     if JLOptions().debug_level == 2
         @timeit "verify 3" (verify_ir(ir, true, false, optimizer_lattice(sv.inlining.interp)); verify_linetable(ir.linetable))
     end

base/compiler/ssair/ir.jl

@@ -946,6 +946,14 @@ function insert_node_here!(compact::IncrementalCompact, newinst::NewInstruction,
     return inst
 end
 
+function delete_inst_here!(compact)
+    # Delete the statement, update refcounts etc
+    compact[compact.idx-1] = nothing
+    # Pretend that we never compacted this statement in the first place
+    compact.idx -= 1
+    return nothing
+end
+
 function getindex(view::TypesView, v::OldSSAValue)
     id = v.id
     ir = view.ir.ir

base/compiler/ssair/passes.jl

@@ -1738,6 +1738,7 @@ function adce_pass!(ir::IRCode, inlining::Union{Nothing,InliningState}=nothing)
     all_phis = Int[]
     unionphis = Pair{Int,Any}[] # sorted
     compact = IncrementalCompact(ir, true)
+    made_changes = false
     for ((_, idx), stmt) in compact
         if isa(stmt, PhiNode)
             push!(all_phis, idx)
@@ -1759,7 +1760,7 @@ function adce_pass!(ir::IRCode, inlining::Union{Nothing,InliningState}=nothing)
                 # nullify safe `typeassert` calls
                 ty, isexact = instanceof_tfunc(argextype(stmt.args[3], compact), true)
                 if isexact && ⊑(𝕃ₒ, argextype(stmt.args[2], compact), ty)
-                    compact[idx] = nothing
+                    delete_inst_here!(compact)
                     continue
                 end
             end
@@ -1801,6 +1802,7 @@ function adce_pass!(ir::IRCode, inlining::Union{Nothing,InliningState}=nothing)
         if t === Union{}
             stmt = compact[SSAValue(phi)][:stmt]::PhiNode
             kill_phi!(compact, phi_uses, 1:length(stmt.values), SSAValue(phi), stmt, true)
+            made_changes = true
             continue
         elseif t === Any
             continue
@@ -1822,16 +1824,17 @@ function adce_pass!(ir::IRCode, inlining::Union{Nothing,InliningState}=nothing)
         end
         compact.result[phi][:type] = t
         kill_phi!(compact, phi_uses, to_drop, SSAValue(phi), stmt, false)
+        made_changes = true
     end
     # Perform simple DCE for unused values
     extra_worklist = Int[]
     for (idx, nused) in Iterators.enumerate(compact.used_ssas)
         idx >= compact.result_idx && break
         nused == 0 || continue
-        adce_erase!(phi_uses, extra_worklist, compact, idx, false)
+        made_changes |= adce_erase!(phi_uses, extra_worklist, compact, idx, false)
     end
     while !isempty(extra_worklist)
-        adce_erase!(phi_uses, extra_worklist, compact, pop!(extra_worklist), true)
+        made_changes |= adce_erase!(phi_uses, extra_worklist, compact, pop!(extra_worklist), true)
     end
     # Go back and erase any phi cycles
     changed = true
@@ -1852,10 +1855,11 @@ function adce_pass!(ir::IRCode, inlining::Union{Nothing,InliningState}=nothing)
         while !isempty(extra_worklist)
             if adce_erase!(phi_uses, extra_worklist, compact, pop!(extra_worklist), true)
                 changed = true
+                made_changes = true
             end
         end
     end
-    return complete(compact)
+    return Pair{IRCode, Bool}(complete(compact), made_changes)
 end
 
 function is_bb_empty(ir::IRCode, bb::BasicBlock)