MIR Gen - Common lvalue for if

6 files changed, 33 insertions, 8 deletions

diff --git a/src/mir/from_hir.cpp b/src/mir/from_hir.cpp
index f3f8f745..04291799 100644
--- a/src/mir/from_hir.cpp
+++ b/src/mir/from_hir.cpp
@@ -750,7 +750,7 @@ namespace {
                 auto scope = m_builder.new_scope_temp( cond->span() );
                 this->visit_node_ptr(*cond_p);
                 ASSERT_BUG(cond->span(), cond->m_res_type == ::HIR::CoreType::Bool, "If condition wasn't a bool");
-                decision_val = m_builder.get_result_in_lvalue(cond->span(), ::HIR::CoreType::Bool);
+                decision_val = m_builder.get_result_in_if_cond(cond->span());
                 m_builder.terminate_scope(cond->span(), mv$(scope));
             }
 
diff --git a/src/mir/from_hir.hpp b/src/mir/from_hir.hpp
index e124770c..07228688 100644
--- a/src/mir/from_hir.hpp
+++ b/src/mir/from_hir.hpp
@@ -159,6 +159,11 @@ class MirBuilder
     ::std::vector<ScopeDef> m_scopes;
     ::std::vector<unsigned int> m_scope_stack;
     ScopeHandle m_fcn_scope;
+
+    // LValue used only for the condition of `if`
+    // - Using a fixed temporary simplifies parts of lowering (scope related) and reduces load on
+    //   the optimiser.
+    ::MIR::LValue   m_if_cond_lval;
 public:
     MirBuilder(const Span& sp, const StaticTraitResolve& resolve, const ::HIR::Function::args_t& args, ::MIR::Function& output);
     ~MirBuilder();
@@ -186,6 +191,17 @@ public:
     /// Obtains a result in a param (or a lvalue)
     ::MIR::Param get_result_in_param(const Span& sp, const ::HIR::TypeRef& ty, bool allow_missing_value=false);
 
+    ::MIR::LValue get_if_cond() const {
+        return m_if_cond_lval.clone();
+    }
+    ::MIR::LValue get_rval_in_if_cond(const Span& sp, ::MIR::RValue val) {
+        push_stmt_assign(sp, m_if_cond_lval.clone(), mv$(val));
+        return m_if_cond_lval.clone();
+    }
+    ::MIR::LValue get_result_in_if_cond(const Span& sp) {
+        return get_rval_in_if_cond(sp, get_result(sp));
+    }
+
     // - Statements
     // Push an assignment. NOTE: This also marks the rvalue as moved
     void push_stmt_assign(const Span& sp, ::MIR::LValue dst, ::MIR::RValue val);
@@ -215,6 +231,7 @@ public:
 
     void set_cur_block(unsigned int new_block);
     ::MIR::BasicBlockId pause_cur_block();
+
     void end_block(::MIR::Terminator term);
 
     ::MIR::BasicBlockId new_bb_linked();
diff --git a/src/mir/from_hir_match.cpp b/src/mir/from_hir_match.cpp
index 2f248f10..ec720d8a 100644
--- a/src/mir/from_hir_match.cpp
+++ b/src/mir/from_hir_match.cpp
@@ -372,8 +372,7 @@ void MIR_LowerHIR_Match( MirBuilder& builder, MirConverter& conv, ::HIR::ExprNod
 
             auto tmp_scope = builder.new_scope_temp(arm.m_cond->span());
             conv.visit_node_ptr( arm.m_cond );
-            ac.cond_lval = builder.get_result_in_lvalue(arm.m_cond->span(), ::HIR::TypeRef(::HIR::CoreType::Bool));
-            // NOTE: Terminating the scope slightly early is safe, because the resulting boolean temp isn't invalidated.
+            ac.cond_lval = builder.get_result_in_if_cond(arm.m_cond->span());
             builder.terminate_scope( arm.m_code->span(), mv$(tmp_scope) );
             ac.cond_end = builder.pause_cur_block();
 
@@ -1947,8 +1946,8 @@ int MIR_LowerHIR_Match_Simple__GeneratePattern(MirBuilder& builder, const Span&
                     auto succ_bb = builder.new_bb_unlinked();
 
                     auto test_val = ::MIR::Param( ::MIR::Constant::make_Uint({ re.as_Uint().v, te }));
-                    auto cmp_lval = builder.lvalue_or_temp(sp, ::HIR::CoreType::Bool, ::MIR::RValue::make_BinOp({ val.clone(), ::MIR::eBinOp::EQ, mv$(test_val) }));
-                    builder.end_block( ::MIR::Terminator::make_If({ mv$(cmp_lval), succ_bb, fail_bb }) );
+                    builder.push_stmt_assign(sp, builder.get_if_cond(), ::MIR::RValue::make_BinOp({ val.clone(), ::MIR::eBinOp::EQ, mv$(test_val) }));
+                    builder.end_block( ::MIR::Terminator::make_If({ builder.get_if_cond(), succ_bb, fail_bb }) );
                     builder.set_cur_block(succ_bb);
                     ),
                 (ValueRange,
@@ -2847,8 +2846,8 @@ void MatchGenGrouped::gen_dispatch__primitive(::HIR::TypeRef ty, ::MIR::LValue v
             ASSERT_BUG(sp, r.is_Value(), "Matching without _Value pattern - " << r.tag_str());
             const auto& re = r.as_Value();
             auto test_val = ::MIR::Param(re.clone());
-            auto cmp_lval = this->push_compare( val.clone(), ::MIR::eBinOp::EQ, mv$(test_val) );
-            m_builder.end_block( ::MIR::Terminator::make_If({ mv$(cmp_lval), arm_targets[0], def_blk }) );
+            auto cmp_lval = m_builder.get_rval_in_if_cond(sp, ::MIR::RValue::make_BinOp({ val.clone(), ::MIR::eBinOp::EQ, mv$(test_val) }));
+            m_builder.end_block( ::MIR::Terminator::make_If({  mv$(cmp_lval), arm_targets[0], def_blk }) );
         }
         else
         {
diff --git a/src/mir/helpers.cpp b/src/mir/helpers.cpp
index 21e16116..d70fda95 100644
--- a/src/mir/helpers.cpp
+++ b/src/mir/helpers.cpp
@@ -502,6 +502,9 @@ namespace {
         bool is_empty() const {
             return start == end;
         }
+        bool is_borrowed() const {
+            return this->end == Position { ~0u, ~0u };
+        }
     };
     static unsigned NEXT_INDEX = 0;
     struct State
@@ -585,10 +588,11 @@ namespace {
         {
             // TODO: This logic isn't quite correct. Just becase a value's existing end is already marked as valid,
             // doesn't mean that we have no new information.
+            // - Wait, doesn't it?
             auto try_merge_lft = [&](const ProtoLifetime& lft, const ::std::vector<unsigned int>& seen)->bool {
                 if(lft.is_empty())  return false;
                 // TODO: What should be done for borrow flagged values
-                if(lft.end == Position { ~0u, ~0u })    return false;
+                if(lft.is_borrowed())   return false;
                 auto end_idx = block_offsets.at( val_state.block_path.at(lft.end.path_index) ) + lft.end.stmt_idx;
 
                 auto it = ::std::find(seen.begin(), seen.end(), end_idx);
diff --git a/src/mir/mir_builder.cpp b/src/mir/mir_builder.cpp
index c023b797..293904df 100644
--- a/src/mir/mir_builder.cpp
+++ b/src/mir/mir_builder.cpp
@@ -32,6 +32,9 @@ MirBuilder::MirBuilder(const Span& sp, const StaticTraitResolve& resolve, const
     m_scopes.push_back( ScopeDef { sp, ScopeType::make_Temporaries({}) } );
     m_scope_stack.push_back( 1 );
 
+
+    m_if_cond_lval = this->new_temporary(::HIR::CoreType::Bool);
+
     m_arg_states.reserve( args.size() );
     for(size_t i = 0; i < args.size(); i ++ )
         m_arg_states.push_back( VarState::make_Valid({}) );
diff --git a/src/mir/optimise.cpp b/src/mir/optimise.cpp
index f66b3240..611b3a9e 100644
--- a/src/mir/optimise.cpp
+++ b/src/mir/optimise.cpp
@@ -1121,6 +1121,8 @@ bool MIR_Optimise_UnifyTemporaries(::MIR::TypeResolve& state, ::MIR::Function& f
             }
             return false;
             });
+
+        // TODO: Replace in ScopeEnd too?
     }
 
     return replacement_needed;