From edea1273c8ea758cfa106f28d720aa1778210c99 Mon Sep 17 00:00:00 2001
From: Mark Thom <markjordanthom@gmail.com>
Date: Fri, 22 Jul 2022 21:34:38 -0600
Subject: [PATCH] trim get_structure and put_structure arities when last arg is
 an index ptr (#1536)

---
 src/codegen.rs | 23 ++++++++++++++++++++++-
 src/targets.rs | 23 -----------------------
 2 files changed, 22 insertions(+), 24 deletions(-)

diff --git a/src/codegen.rs b/src/codegen.rs
index 2a9d5b62..ec69f277 100644
--- a/src/codegen.rs
+++ b/src/codegen.rs
@@ -263,6 +263,27 @@ impl DebrayAllocator {
     }
 }
 
+// if the final argument of the structure is a Literal::Index,
+// decrement the arity of the PutStructure instruction by 1.
+fn trim_structure_by_last_arg(instr: &mut Instruction, last_arg: &Term) {
+    match instr {
+        Instruction::PutStructure(_, ref mut arity, _) |
+        Instruction::GetStructure(_, ref mut arity, _) => {
+            if let Term::Literal(_, Literal::CodeIndex(_)) = last_arg {
+                // it is acceptable if arity == 0 is the result of
+                // this decrement. call/N will have to read the index
+                // constant for '$call_inline' to succeed. to find it,
+                // it must know the heap location of the index.
+                // self.store must stop before reading the atom into a
+                // register.
+
+                *arity -= 1;
+            }
+        }
+        _ => {}
+    }
+}
+
 impl<'b> CodeGenerator<'b> {
     pub(crate) fn new(atom_tbl: &'b mut AtomTable, settings: CodeGenSettings) -> Self {
         CodeGenerator {
@@ -375,7 +396,7 @@ impl<'b> CodeGenerator<'b> {
 
                     if let Some(instr) = target.last_mut() {
                         if let Some(term) = terms.last() {
-                            Target::trim_structure_by_last_arg(instr, term);
+                            trim_structure_by_last_arg(instr, term);
                         }
                     }
 
diff --git a/src/targets.rs b/src/targets.rs
index ef1d94a8..cbb469f9 100644
--- a/src/targets.rs
+++ b/src/targets.rs
@@ -36,8 +36,6 @@ pub(crate) trait CompilationTarget<'a> {
     fn subterm_to_value(r: RegType) -> Instruction;
 
     fn clause_arg_to_instr(r: RegType) -> Instruction;
-
-    fn trim_structure_by_last_arg(instr: &mut Instruction, last_arg: &Term);
 }
 
 impl<'a> CompilationTarget<'a> for FactInstruction {
@@ -108,10 +106,6 @@ impl<'a> CompilationTarget<'a> for FactInstruction {
     fn clause_arg_to_instr(val: RegType) -> Instruction {
         Instruction::UnifyVariable(val)
     }
-
-    fn trim_structure_by_last_arg(_instr: &mut Instruction, _last_arg: &Term) {
-        // a no-op for facts.
-    }
 }
 
 impl<'a> CompilationTarget<'a> for QueryInstruction {
@@ -182,21 +176,4 @@ impl<'a> CompilationTarget<'a> for QueryInstruction {
     fn clause_arg_to_instr(val: RegType) -> Instruction {
         Instruction::SetValue(val)
     }
-
-    // if the final argument of the structure is a Literal::Index,
-    // decrement the arity of the PutStructure instruction by 1.
-    fn trim_structure_by_last_arg(instr: &mut Instruction, last_arg: &Term) {
-        if let Instruction::PutStructure(_, ref mut arity, _) = instr {
-            if let Term::Literal(_, Literal::CodeIndex(_)) = last_arg {
-                // it is acceptable if arity == 0 is the result of
-                // this decrement. call/N will have to read the index
-                // constant for '$call_inline' to succeed. to find it,
-                // it must know the heap location of the index.
-                // self.store must stop before reading the atom into a
-                // register.
-
-                *arity -= 1;
-            }
-        }
-    }
 }
-- 
2.54.0