From cf241951a0197ddc1851c4d15b64005809506d06 Mon Sep 17 00:00:00 2001
From: Stefano Sanfilippo <a.little.coder@gmail.com>
Date: Mon, 9 Mar 2015 22:04:10 +0100
Subject: [PATCH] Ensure that basic blocks in loops and branches are well
 formed.

---
 BitcodeEmitter.cpp | 47 ++++++++++++++++++++++++++++------------------
 BitcodeEmitter.hpp |  3 +++
 2 files changed, 32 insertions(+), 18 deletions(-)

diff --git a/BitcodeEmitter.cpp b/BitcodeEmitter.cpp
index 1eda9f3..d8f548d 100644
--- a/BitcodeEmitter.cpp
+++ b/BitcodeEmitter.cpp
@@ -263,11 +263,14 @@ bool BitcodeEmitter::emit(Loop const& node) {
     d->builder.CreateBr(body);
     d->builder.SetInsertPoint(body);
 
-    d->scope.enter();
-    for (Statement const& statement: node.getBody()) {
-        GUARDED(statement.emit(this));
-    }
-    d->scope.leave();
+    llvm::BasicBlock *condition = llvm::BasicBlock::Create(
+        getGlobalContext(), "loopcondition"
+    );
+
+    GUARDED(ensureBasicBlock(node.getBody(), condition));
+
+    father->getBasicBlockList().push_back(condition);
+    d->builder.SetInsertPoint(condition);
 
     GUARDED(node.getCondition().emit(this));
 
@@ -467,12 +470,8 @@ bool BitcodeEmitter::emit(Branch const& node) {
             isTrue(d, d->retval, "condition"), thenbb, elsebb
         );
         d->builder.SetInsertPoint(thenbb);
-        d->scope.enter();
-        for (Statement const& statement: cas.getBody()) {
-            GUARDED(statement.emit(this));
-        }
-        d->scope.leave();
-        d->builder.CreateBr(mergebb);
+
+        GUARDED(ensureBasicBlock(cas.getBody(), mergebb));
 
         func->getBasicBlockList().push_back(elsebb);
         d->builder.SetInsertPoint(elsebb);
@@ -484,12 +483,7 @@ bool BitcodeEmitter::emit(Branch const& node) {
     }
 
     if (body.getElse()) {
-        d->scope.enter();
-        for (Statement const& statement: *body.getElse()) {
-            GUARDED(statement.emit(this));
-        }
-        d->scope.leave();
-        d->builder.CreateBr(mergebb);
+        GUARDED(ensureBasicBlock(*body.getElse(), mergebb));
     }
 
     func->getBasicBlockList().push_back(mergebb);
@@ -590,7 +584,10 @@ bool BitcodeEmitter::emit(Function const& node) {
 
     d->scope.leave();
 
-    d->builder.CreateBr(d->funcExit);
+    if (!d->builder.GetInsertBlock()->getTerminator()) {
+        d->builder.CreateBr(d->funcExit);
+    }
+
     func->getBasicBlockList().push_back(d->funcExit);
     d->builder.SetInsertPoint(d->funcExit);
 
@@ -757,3 +754,17 @@ bool BitcodeEmitter::emitSemiExpression(Id const& left, SemiExpression const& ri
     return true;
 }
 
+bool BitcodeEmitter::ensureBasicBlock(PointerList<Statement> const& statements, llvm::BasicBlock *after) {
+    d->scope.enter();
+    for (Statement const& statement: statements) {
+        GUARDED(statement.emit(this));
+    }
+    d->scope.leave();
+
+    if (!d->builder.GetInsertBlock()->getTerminator()) {
+        d->builder.CreateBr(after);
+    }
+
+    return true;
+}
+
diff --git a/BitcodeEmitter.hpp b/BitcodeEmitter.hpp
index a654db6..2a716a2 100644
--- a/BitcodeEmitter.hpp
+++ b/BitcodeEmitter.hpp
@@ -27,11 +27,13 @@
 namespace llvm {
     class Module;
     class Function;
+    class BasicBlock;
 }
 
 namespace monicelli {
 
 class SemiExpression;
+class Statement;
 
 class BitcodeEmitter: public Emitter {
 public:
@@ -67,6 +69,7 @@ public:
 
 private:
     bool emitSemiExpression(Id const& left, SemiExpression const& right);
+    bool ensureBasicBlock(PointerList<Statement> const& statements, llvm::BasicBlock *after);
 
     Pointer<llvm::Module> module;
     Private *d;