From 828cb1065f1681a46eec684e1c524c56cf42ad6f Mon Sep 17 00:00:00 2001
From: Jameson Nash <vtjnash@gmail.com>
Date: Wed, 9 Nov 2016 14:33:28 -0500
Subject: [PATCH] add fast-path to inference schanged computation

when merging two frames (such as when handling exception frames),
most of the time new is old, but the computation here is
exponential in the number of variables so we want the inner computation
here to be ultra-fast in the common case

fix #15346
---
 base/inference.jl | 27 +++++++++------------------
 1 file changed, 9 insertions(+), 18 deletions(-)

diff --git a/base/inference.jl b/base/inference.jl
index 23c563da07ab4..74da56eeeb370 100644
--- a/base/inference.jl
+++ b/base/inference.jl
@@ -1416,27 +1416,28 @@ function tmerge(typea::ANY, typeb::ANY)
 end
 
 function smerge(sa::Union{NotFound,VarState}, sb::Union{NotFound,VarState})
+    sa === sb && return sa
     sa === NF && return sb
     sb === NF && return sa
-    issubstate(sa,sb) && return sb
-    issubstate(sb,sa) && return sa
-    VarState(tmerge(sa.typ, sb.typ), sa.undef | sb.undef)
+    issubstate(sa, sb) && return sb
+    issubstate(sb, sa) && return sa
+    return VarState(tmerge(sa.typ, sb.typ), sa.undef | sb.undef)
 end
 
-tchanged(n::ANY, o::ANY) = o===NF || (n!==NF && !(n ⊑ o))
-schanged(n::ANY, o::ANY) = o===NF || (n!==NF && !issubstate(n, o))
+@inline tchanged(n::ANY, o::ANY) = o === NF || (n !== NF && !(n ⊑ o))
+@inline schanged(n::ANY, o::ANY) = (n !== o) && (o === NF || (n !== NF && !issubstate(n, o)))
 
 function stupdate!(state::Tuple{}, changes::StateUpdate)
     newst = copy(changes.state)
     if isa(changes.var, Slot)
         newst[changes.var.id] = changes.vtype
     end
-    newst
+    return newst
 end
 
 function stupdate!(state::VarTable, change::StateUpdate)
     for i = 1:length(state)
-        if isa(change.var,Slot) && i == change.var.id
+        if isa(change.var, Slot) && i == (change.var::Slot).id
             newtype = change.vtype
         else
             newtype = change.state[i]
@@ -1794,8 +1795,8 @@ function typeinf_frame(frame)
             changes = abstract_interpret(stmt, s[pc]::Array{Any,1}, frame)
             if changes === ()
                 # this line threw an error and there is no need to continue
+                #changes = s[pc]
                 break
-                changes = s[pc]
             end
             if frame.cur_hand !== ()
                 # propagate type info to exception handler
@@ -1872,16 +1873,6 @@ function typeinf_frame(frame)
                         push!(W, l)
                         s[l] = newstate
                     end
-#                        if frame.handler_at[l] === 0
-#                            frame.n_handlers += 1
-#                            if frame.n_handlers > 25
-#                                # too many exception handlers slows down inference a lot.
-#                                # for an example see test/libgit2.jl on 0.5-pre master
-#                                # around e.g. commit c072d1ce73345e153e4fddf656cda544013b1219
-#                                inference_stack = (inference_stack::CallStack).prev
-#                                return (ast0, Any, false)
-#                            end
-#                        end
                     frame.handler_at[l] = frame.cur_hand
                 elseif hd === :leave
                     for i = 1:((stmt.args[1])::Int)