From f261a534cc96d41cee15462795844116887bd99a Mon Sep 17 00:00:00 2001
From: Ulf Hermann <ulf.hermann@qt.io>
Date: Fri, 31 Mar 2017 15:52:47 +0200
Subject: V4: Set correct source locations for jumps out of conditionals

We always want to place the jump on the last line of the conditionally
executed statement, unless we might never execute the last line.

In the latter case, that is if the inner statement is again a
conditional, we use some token of the outer condition. This works fine
with loops, as the loop condition is actually checked after each
iteration, and it's plausible to the user that we jump there.

With "if" statements, it's not so great. We cannot really explain why we
jump back to the "if" token after executing the conditional statement.
However, we have to add some source location to the jump instruction as
otherwise it uses the source location of the last statement that had
one, which is rather random.

Task-number: QTBUG-59204
Task-number: QTBUG-59774
Change-Id: I48e331ce1c1830f236e16b75c9201a2f490d2092
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
---
 src/qml/compiler/qv4codegen.cpp | 37 +++++++++++++++++++++++++++++--------
 1 file changed, 29 insertions(+), 8 deletions(-)

(limited to 'src')

diff --git a/src/qml/compiler/qv4codegen.cpp b/src/qml/compiler/qv4codegen.cpp
index a10c0730bf..fcfbdfa74b 100644
--- a/src/qml/compiler/qv4codegen.cpp
+++ b/src/qml/compiler/qv4codegen.cpp
@@ -92,6 +92,27 @@ static bool cjumpCanHandle(IR::AluOp op)
     }
 }
 
+static inline void setJumpOutLocation(IR::Stmt *s, const Statement *body,
+                                      const SourceLocation &fallback)
+{
+    switch (body->kind) {
+    // Statements where we might never execute the last line.
+    // Use the fallback.
+    case Statement::Kind_ConditionalExpression:
+    case Statement::Kind_ForEachStatement:
+    case Statement::Kind_ForStatement:
+    case Statement::Kind_IfStatement:
+    case Statement::Kind_LocalForEachStatement:
+    case Statement::Kind_LocalForStatement:
+    case Statement::Kind_WhileStatement:
+        setLocation(s, fallback);
+        break;
+    default:
+        setLocation(s, body->lastSourceLocation());
+        break;
+    }
+}
+
 Codegen::ScanFunctions::ScanFunctions(Codegen *cg, const QString &sourceCode, CompilationMode defaultProgramMode)
     : _cg(cg)
     , _sourceCode(sourceCode)
@@ -2256,7 +2277,7 @@ bool Codegen::visit(DoWhileStatement *ast)
 
     _block = loopbody;
     statement(ast->statement);
-    setLocation(_block->JUMP(loopcond), ast->statement->lastSourceLocation());
+    setJumpOutLocation(_block->JUMP(loopcond), ast->statement, ast->semicolonToken);
 
     _block = loopcond;
     condition(ast->expression, loopbody, loopend);
@@ -2321,7 +2342,7 @@ bool Codegen::visit(ForEachStatement *ast)
         return false;
     move(*init, _block->TEMP(temp));
     statement(ast->statement);
-    setLocation(_block->JUMP(foreachin), ast->lastSourceLocation());
+    setJumpOutLocation(_block->JUMP(foreachin), ast->statement, ast->forToken);
 
     _block = foreachin;
 
@@ -2360,7 +2381,7 @@ bool Codegen::visit(ForStatement *ast)
 
     _block = forbody;
     statement(ast->statement);
-    setLocation(_block->JUMP(forstep), ast->lastSourceLocation());
+    setJumpOutLocation(_block->JUMP(forstep), ast->statement, ast->forToken);
 
     _block = forstep;
     statement(ast->expression);
@@ -2386,12 +2407,12 @@ bool Codegen::visit(IfStatement *ast)
 
     _block = iftrue;
     statement(ast->ok);
-    _block->JUMP(endif);
+    setJumpOutLocation(_block->JUMP(endif), ast->ok, ast->ifToken);
 
     if (ast->ko) {
         _block = iffalse;
         statement(ast->ko);
-        _block->JUMP(endif);
+        setJumpOutLocation(_block->JUMP(endif), ast->ko, ast->elseToken);
     }
 
     _block = endif;
@@ -2460,7 +2481,7 @@ bool Codegen::visit(LocalForEachStatement *ast)
     int temp = _block->newTemp();
     move(identifier(ast->declaration->name.toString()), _block->TEMP(temp));
     statement(ast->statement);
-    setLocation(_block->JUMP(foreachin), ast->lastSourceLocation());
+    setJumpOutLocation(_block->JUMP(foreachin), ast->statement, ast->forToken);
 
     _block = foreachin;
 
@@ -2499,7 +2520,7 @@ bool Codegen::visit(LocalForStatement *ast)
 
     _block = forbody;
     statement(ast->statement);
-    setLocation(_block->JUMP(forstep), ast->lastSourceLocation());
+    setJumpOutLocation(_block->JUMP(forstep), ast->statement, ast->forToken);
 
     _block = forstep;
     statement(ast->expression);
@@ -2800,7 +2821,7 @@ bool Codegen::visit(WhileStatement *ast)
 
     _block = whilebody;
     statement(ast->statement);
-    setLocation(_block->JUMP(whilecond), ast->lastSourceLocation());
+    setJumpOutLocation(_block->JUMP(whilecond), ast->statement, ast->whileToken);
 
     _block = whileend;
     leaveLoop();
-- 
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