From 71b21b2668c95073a0af7b1d0214c1e5c561cec4 Mon Sep 17 00:00:00 2001
From: Christophe de Dinechin <christophe@dinechin.org>
Date: Fri, 2 Apr 2021 08:40:32 +0200
Subject: [PATCH] bytecode: Do not treat perfect type matches as conditional

When matching [write "Hello"] with [write X:text], we don't want to consider the
generated code as conditional when it is not.

This changes the generated code from:

Compiled write "false" as
Constants:
  C0	= "false"
  C1	= false
  C2	= true
Locals:
  L0	= [write "false"]
  L1	= ["false"]
Types:
  write "false"	as	nil
  "false"	as	character
Opcodes (2 locals, 0 parameters, 2 temporaries)
     0: native              #41=xl_write_text, (1)
       0: C0
       => L0
     5: branch              +12=19
     7: character_typecheck L1, +7=17
    10: native              #39=xl_write_character, (1)
       0: C0
       => L0
    15: branch              +2=19
    17: form_error          L0
    19: ret                 L0

to:

Compiled write "false" as
Constants:
  C0	= "false"
  C1	= false
  C2	= true
Locals:
  L0	= [write "false"]
Types:
  write "false"	as	nil
  "false"	as	text
Opcodes (1 locals, 0 parameters, 1 temporaries)
     0: native              #41=xl_write_text, (1)
       0: C0
       => L0
     5: ret                 L0

Signed-off-by: Christophe de Dinechin <christophe@dinechin.org>
---
 src/bytecode.cpp | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/src/bytecode.cpp b/src/bytecode.cpp
index 786677601..b8c07c51e 100644
--- a/src/bytecode.cpp
+++ b/src/bytecode.cpp
@@ -2164,6 +2164,7 @@ strength BytecodeBindings::Do(Infix *what)
         if (outermost)
         {
             type = want;
+            have = want;
         }
         else if (want != have)
         {
@@ -2190,7 +2191,7 @@ strength BytecodeBindings::Do(Infix *what)
             OP(check_input_type, want, ValueIndex(test), CHECK);
         }
         bytecode->Type(value, want);
-        return Possible();
+        return want == have ? Perfect() : Possible();
     }
 
     // Make sure names bind to values
@@ -2349,8 +2350,6 @@ inline Context::LookupMode lookupMode(Bytecode *bytecode)
 }
 
 
-static void debug(Tree *expr, Tree *decl) {}
-
 static Tree *lookupCandidate(Scope   *evalScope,
                              Scope   *declScope,
                              Tree    *expr,
@@ -2366,12 +2365,6 @@ static Tree *lookupCandidate(Scope   *evalScope,
     Tree *pattern = decl->Pattern();
     XL_ASSERT(bindings.Self() == expr);
 
-if (Prefix *prefix = expr->AsPrefix())
-    if (Name *name = prefix->left->AsName())
-        if (name->value == "write")
-            if (Text *text = prefix->right->AsText())
-                debug(expr, decl);
-
     // Add bytecode to check argument against parameters and create locals
     Bytecode::Attempt attempt(bytecode);
     bindings.Candidate(decl, evalScope, declScope);