Optimize away try/catch blocks that are known not to trigger (#51674)

This leverages the support from #51590 to delete any try catch block
that is known not to be triggered (either because the try-body is empty
to because we have proven `:nothrow` for all contained statements).

base/compiler/abstractinterpretation.jl

@@ -2981,6 +2981,20 @@ function update_bestguess!(interp::AbstractInterpreter, frame::InferenceState,
     end
 end
 
+function propagate_to_error_handler!(frame::InferenceState, currpc::Int, W::BitSet, 𝕃ᵢ::AbstractLattice, currstate::VarTable)
+    # If this statement potentially threw, propagate the currstate to the
+    # exception handler, BEFORE applying any state changes.
+    cur_hand = frame.handler_at[currpc]
+    if cur_hand != 0
+        enter = frame.src.code[cur_hand]::Expr
+        l = enter.args[1]::Int
+        exceptbb = block_for_inst(frame.cfg, l)
+        if update_bbstate!(𝕃ᵢ, frame, exceptbb, currstate)
+            push!(W, exceptbb)
+        end
+    end
+end
+
 # make as much progress on `frame` as possible (without handling cycles)
 function typeinf_local(interp::AbstractInterpreter, frame::InferenceState)
     @assert !is_inferred(frame)
@@ -3037,6 +3051,7 @@ function typeinf_local(interp::AbstractInterpreter, frame::InferenceState)
                     if nothrow
                         add_curr_ssaflag!(frame, IR_FLAG_NOTHROW)
                     else
+                        propagate_to_error_handler!(frame, currpc, W, 𝕃ᵢ, currstate)
                         merge_effects!(interp, frame, EFFECTS_THROWS)
                     end
 
@@ -3107,12 +3122,9 @@ function typeinf_local(interp::AbstractInterpreter, frame::InferenceState)
                     ssavaluetypes[frame.currpc] = Any
                     @goto find_next_bb
                 elseif isexpr(stmt, :enter)
-                    # Propagate entry info to exception handler
-                    l = stmt.args[1]::Int
-                    catchbb = block_for_inst(frame.cfg, l)
-                    if update_bbstate!(𝕃ᵢ, frame, catchbb, currstate)
-                        push!(W, catchbb)
-                    end
+                    ssavaluetypes[currpc] = Any
+                    @goto fallthrough
+                elseif isexpr(stmt, :leave)
                     ssavaluetypes[currpc] = Any
                     @goto fallthrough
                 end
@@ -3121,26 +3133,15 @@ function typeinf_local(interp::AbstractInterpreter, frame::InferenceState)
             # Process non control-flow statements
             (; changes, type) = abstract_eval_basic_statement(interp,
                 stmt, currstate, frame)
+            if (get_curr_ssaflag(frame) & IR_FLAG_NOTHROW) != IR_FLAG_NOTHROW
+                propagate_to_error_handler!(frame, currpc, W, 𝕃ᵢ, currstate)
+            end
             if type === Bottom
                 ssavaluetypes[currpc] = Bottom
                 @goto find_next_bb
             end
             if changes !== nothing
                 stoverwrite1!(currstate, changes)
-                let cur_hand = frame.handler_at[currpc], l, enter
-                    while cur_hand != 0
-                        enter = frame.src.code[cur_hand]::Expr
-                        l = enter.args[1]::Int
-                        exceptbb = block_for_inst(frame.cfg, l)
-                        # propagate new type info to exception handler
-                        # the handling for Expr(:enter) propagates all changes from before the try/catch
-                        # so this only needs to propagate any changes
-                        if stupdate1!(𝕃ᵢ, states[exceptbb]::VarTable, changes)
-                            push!(W, exceptbb)
-                        end
-                        cur_hand = frame.handler_at[cur_hand]
-                    end
-                end
             end
             if type === nothing
                 ssavaluetypes[currpc] = Any

base/compiler/optimize.jl

@@ -839,27 +839,35 @@ function convert_to_ircode(ci::CodeInfo, sv::OptimizationState)
     code = copy_exprargs(ci.code)
     for i = 1:length(code)
         expr = code[i]
-        if !(i in sv.unreachable) && isa(expr, GotoIfNot)
-            # Replace this live GotoIfNot with:
-            # - no-op if :nothrow and the branch target is unreachable
-            # - cond if :nothrow and both targets are unreachable
-            # - typeassert if must-throw
-            block = block_for_inst(sv.cfg, i)
-            if ssavaluetypes[i] === Bottom
-                destblock = block_for_inst(sv.cfg, expr.dest)
-                cfg_delete_edge!(sv.cfg, block, block + 1)
-                ((block + 1) != destblock) && cfg_delete_edge!(sv.cfg, block, destblock)
-                expr = Expr(:call, Core.typeassert, expr.cond, Bool)
-            elseif i + 1 in sv.unreachable
-                @assert (ci.ssaflags[i] & IR_FLAG_NOTHROW) != 0
-                cfg_delete_edge!(sv.cfg, block, block + 1)
-                expr = GotoNode(expr.dest)
-            elseif expr.dest in sv.unreachable
-                @assert (ci.ssaflags[i] & IR_FLAG_NOTHROW) != 0
-                cfg_delete_edge!(sv.cfg, block, block_for_inst(sv.cfg, expr.dest))
-                expr = nothing
+        if !(i in sv.unreachable)
+            if isa(expr, GotoIfNot)
+                # Replace this live GotoIfNot with:
+                # - no-op if :nothrow and the branch target is unreachable
+                # - cond if :nothrow and both targets are unreachable
+                # - typeassert if must-throw
+                block = block_for_inst(sv.cfg, i)
+                if ssavaluetypes[i] === Bottom
+                    destblock = block_for_inst(sv.cfg, expr.dest)
+                    cfg_delete_edge!(sv.cfg, block, block + 1)
+                    ((block + 1) != destblock) && cfg_delete_edge!(sv.cfg, block, destblock)
+                    expr = Expr(:call, Core.typeassert, expr.cond, Bool)
+                elseif i + 1 in sv.unreachable
+                    @assert (ci.ssaflags[i] & IR_FLAG_NOTHROW) != 0
+                    cfg_delete_edge!(sv.cfg, block, block + 1)
+                    expr = GotoNode(expr.dest)
+                elseif expr.dest in sv.unreachable
+                    @assert (ci.ssaflags[i] & IR_FLAG_NOTHROW) != 0
+                    cfg_delete_edge!(sv.cfg, block, block_for_inst(sv.cfg, expr.dest))
+                    expr = nothing
+                end
+                code[i] = expr
+            elseif isexpr(expr, :enter)
+                catchdest = expr.args[1]::Int
+                if catchdest in sv.unreachable
+                    cfg_delete_edge!(sv.cfg, block_for_inst(sv.cfg, i), block_for_inst(sv.cfg, catchdest))
+                    code[i] = nothing
+                end
             end
-            code[i] = expr
         end
     end
 
@@ -1239,7 +1247,12 @@ function renumber_ir_elements!(body::Vector{Any}, ssachangemap::Vector{Int}, lab
             end
             if el.head === :enter
                 tgt = el.args[1]::Int
-                el.args[1] = tgt + labelchangemap[tgt]
+                was_deleted = labelchangemap[tgt] == typemin(Int)
+                if was_deleted
+                    body[i] = nothing
+                else
+                    el.args[1] = tgt + labelchangemap[tgt]
+                end
             elseif !is_meta_expr_head(el.head)
                 args = el.args
                 for i = 1:length(args)

base/compiler/ssair/ir.jl

@@ -1364,6 +1364,21 @@ function process_node!(compact::IncrementalCompact, result_idx::Int, inst::Instr
                 ssa_rename[idx] = nothing
                 return result_idx
             end
+        elseif isexpr(stmt, :leave)
+            let i = 1
+                while i <= length(stmt.args)
+                    if stmt.args[i] === nothing
+                        deleteat!(stmt.args, i)
+                    else
+                        i += 1
+                    end
+                end
+            end
+            if isempty(stmt.args)
+                # This :leave is dead
+                ssa_rename[idx] = nothing
+                return result_idx
+            end
         end
         typ = inst[:type]
         if isa(typ, Const) && is_inlineable_constant(typ.val)

base/compiler/ssair/slot2ssa.jl

@@ -875,7 +875,8 @@ function construct_ssa!(ci::CodeInfo, ir::IRCode, sv::OptimizationState,
                 new_code[idx] = GotoIfNot(stmt.cond, new_dest)
             end
         elseif isexpr(stmt, :enter)
-            new_code[idx] = Expr(:enter, block_for_inst(cfg, stmt.args[1]::Int))
+            except_bb = block_for_inst(cfg, stmt.args[1]::Int)
+            new_code[idx] = Expr(:enter, except_bb)
             ssavalmap[idx] = SSAValue(idx) # Slot to store token for pop_exception
         elseif isexpr(stmt, :leave) || isexpr(stmt, :(=)) || isa(stmt, ReturnNode) ||
             isexpr(stmt, :meta) || isa(stmt, NewvarNode)

base/compiler/typelattice.jl

@@ -759,24 +759,6 @@ function stupdate!(lattice::AbstractLattice, state::VarTable, changes::VarTable)
     return changed
 end
 
-function stupdate1!(lattice::AbstractLattice, state::VarTable, change::StateUpdate)
-    changeid = slot_id(change.var)
-    for i = 1:length(state)
-        invalidated = invalidate_slotwrapper(state[i], changeid, change.conditional)
-        if invalidated !== nothing
-            state[i] = invalidated
-        end
-    end
-    # and update the type of it
-    newtype = change.vtype
-    oldtype = state[changeid]
-    if schanged(lattice, newtype, oldtype)
-        state[changeid] = smerge(lattice, oldtype, newtype)
-        return true
-    end
-    return false
-end
-
 function stoverwrite!(state::VarTable, newstate::VarTable)
     for i = 1:length(state)
         state[i] = newstate[i]

src/codegen.cpp

@@ -5180,14 +5180,19 @@ static void emit_ssaval_assign(jl_codectx_t &ctx, ssize_t ssaidx_0based, jl_valu
     ctx.ssavalue_assigned[ssaidx_0based] = true;
 }
 
-static void emit_varinfo_assign(jl_codectx_t &ctx, jl_varinfo_t &vi, jl_cgval_t rval_info, jl_value_t *l=NULL)
+static void emit_varinfo_assign(jl_codectx_t &ctx, jl_varinfo_t &vi, jl_cgval_t rval_info, jl_value_t *l=NULL, bool allow_mismatch=false)
 {
     if (!vi.used || vi.value.typ == jl_bottom_type)
         return;
 
     // convert rval-type to lval-type
     jl_value_t *slot_type = vi.value.typ;
-    rval_info = convert_julia_type(ctx, rval_info, slot_type);
+    // If allow_mismatch is set, type mismatches will not result in traps.
+    // This is used for upsilon nodes, where the destination can have a narrower
+    // type than the store, if inference determines that the store is never read.
+    Value *dummy = NULL;
+    Value **skip = allow_mismatch ? &dummy : NULL;
+    rval_info = convert_julia_type(ctx, rval_info, slot_type, skip);
     if (rval_info.typ == jl_bottom_type)
         return;
 
@@ -5284,7 +5289,7 @@ static void emit_upsilonnode(jl_codectx_t &ctx, ssize_t phic, jl_value_t *val)
             // was unreachable and dead
             val = NULL;
         else
-            emit_varinfo_assign(ctx, vi, rval_info);
+            emit_varinfo_assign(ctx, vi, rval_info, NULL, true);
     }
     if (!val) {
         if (vi.boxroot) {

test/compiler/inference.jl

@@ -5284,3 +5284,72 @@ end
 @test only(Base.return_types((x,f) -> getfield(x, f), (An51317, Symbol))) === Int
 @test only(Base.return_types(x -> getfield(x, :b), (A51317,))) === Union{}
 @test only(Base.return_types(x -> getfield(x, :b), (An51317,))) === Union{}
+
+# Don't visit the catch block for empty try/catch
+function completely_dead_try_catch()
+    try
+    catch
+        return 2.0
+    end
+    return 1
+end
+@test Base.return_types(completely_dead_try_catch) |> only === Int
+@test fully_eliminated(completely_dead_try_catch)
+
+function nothrow_try_catch()
+    try
+        1+1
+    catch
+        return 2.0
+    end
+    return 1
+end
+@test Base.return_types(nothrow_try_catch) |> only === Int
+@test fully_eliminated(nothrow_try_catch)
+
+may_error(b) = Base.inferencebarrier(b) && error()
+function phic_type1()
+    a = 1
+    try
+        may_error(false)
+        a = 1.0
+    catch
+        return a
+    end
+    return 2
+end
+@test Base.return_types(phic_type1) |> only === Int
+@test phic_type1() === 2
+
+function phic_type2()
+    a = 1
+    try
+        may_error(false)
+        a = 1.0
+        may_error(false)
+    catch
+        return a
+    end
+    return 2
+end
+@test Base.return_types(phic_type2) |> only === Union{Int, Float64}
+@test phic_type2() === 2
+
+function phic_type3()
+    a = 1
+    try
+        may_error(false)
+        a = 1.0
+        may_error(false)
+        if Base.inferencebarrier(false)
+            a = Ref(1)
+        elseif Base.inferencebarrier(false)
+            a = nothing
+        end
+    catch
+        return a
+    end
+    return 2
+end
+@test Base.return_types(phic_type3) |> only === Union{Int, Float64}
+@test phic_type3() === 2