Fix bug and leak in relooper merge consecutive blocks (#2159)

Fixes in Relooper merge consecutive blocks:

    Entry block getting removed when it is part of a loop:

bb1->AddBranchTo(bb2, nullptr);
bb1->AddBranchTo(bb3, ...);
bb2->AddBranchTo(bb1, nullptr);
bb3->AddBranchTo(bb4, nullptr);
relooper.AddBlock(bb1);
relooper.AddBlock(bb2);
relooper.AddBlock(bb3);
relooper.AddBlock(bb4);
relooper.Calculate(bb1);

    Branches memory leak

Author: hobby8

src/cfg/Relooper.cpp

@@ -533,7 +533,10 @@ struct Liveness : public RelooperRecursor {
 typedef std::pair<Branch*, Block*> BranchBlock;
 
 struct Optimizer : public RelooperRecursor {
-  Optimizer(Relooper* Parent) : RelooperRecursor(Parent) {
+  Block* Entry;
+
+  Optimizer(Relooper* Parent, Block* EntryInit)
+    : RelooperRecursor(Parent), Entry(EntryInit) {
     // TODO: there are likely some rare but possible O(N^2) cases with this
     // looping
     bool More = true;
@@ -726,6 +729,7 @@ struct Optimizer : public RelooperRecursor {
         NumPredecessors[NextBlock]++;
       }
     }
+    NumPredecessors[Entry]++;
     for (auto* CurrBlock : Parent->Blocks) {
       if (CurrBlock->BranchesOut.size() == 1) {
         auto iter = CurrBlock->BranchesOut.begin();
@@ -744,6 +748,9 @@ struct Optimizer : public RelooperRecursor {
             Builder.makeSequence(CurrBlock->Code, NextBlock->Code);
           // Use the next block's branching behavior
           CurrBlock->BranchesOut.swap(NextBlock->BranchesOut);
+          for (auto& iter : NextBlock->BranchesOut) {
+            delete iter.second;
+          }
           NextBlock->BranchesOut.clear();
           CurrBlock->SwitchCondition = NextBlock->SwitchCondition;
           // The next block now has no predecessors.
@@ -1032,7 +1039,7 @@ struct Optimizer : public RelooperRecursor {
 
 void Relooper::Calculate(Block* Entry) {
   // Optimize.
-  Optimizer(this);
+  Optimizer(this, Entry);
 
   // Find live blocks.
   Liveness Live(this);

test/example/relooper-merge7.c

@@ -0,0 +1,49 @@
+
+#include <assert.h>
+#include <stdio.h>
+
+#include "binaryen-c.h"
+
+int main() {
+  BinaryenModuleRef module = BinaryenModuleCreate();
+
+  RelooperRef relooper = RelooperCreate(module);
+
+  // Create the basic blocks
+  RelooperBlockRef b[4];
+  int hasTerminator[4] = {0, 0, 0, 1};
+
+  int numBlocks = sizeof(b) / sizeof(RelooperBlockRef);
+  assert(sizeof(hasTerminator) / sizeof(int) == numBlocks);
+  int i;
+  for (i = 0; i < numBlocks; i++) {
+    BinaryenExpressionRef args[] = {
+      BinaryenConst(module, BinaryenLiteralInt32(i))};
+    BinaryenExpressionRef list[] = {
+      BinaryenCall(module, "print", args, 1, BinaryenTypeNone()),
+      BinaryenReturn(module, NULL) // relevant only if hasTerminator[i]
+    };
+    b[i] = RelooperAddBlock(
+      relooper,
+      BinaryenBlock(
+        module, NULL, list, 1 + hasTerminator[i], BinaryenTypeNone()));
+  }
+
+  // Create the branches.
+  // In this testcase, only b[2] and b[3] can be merged.
+  RelooperAddBranch(b[0], b[1], NULL, NULL);
+  RelooperAddBranch(
+    b[0], b[2], BinaryenConst(module, BinaryenLiteralInt32(-10)), NULL);
+  RelooperAddBranch(b[1], b[0], NULL, NULL);
+  RelooperAddBranch(b[2], b[3], NULL, NULL);
+
+  BinaryenExpressionRef all = RelooperRenderAndDispose(relooper, b[0], 1);
+
+  // Print it out
+  BinaryenExpressionPrint(all);
+
+  // Clean up the module, which owns all the objects we created above
+  BinaryenModuleDispose(module);
+
+  return 0;
+}

test/example/relooper-merge7.txt

@@ -0,0 +1,37 @@
+(block
+ (block $block$3$break
+  (loop $shape$0$continue
+   (block $block$2$break
+    (call $print
+     (i32.const 0)
+    )
+    (if
+     (i32.const -10)
+     (br $block$3$break)
+     (br $block$2$break)
+    )
+   )
+   (block
+    (call $print
+     (i32.const 1)
+    )
+    (block
+     (br $shape$0$continue)
+    )
+   )
+  )
+ )
+ (block
+  (block
+   (call $print
+    (i32.const 2)
+   )
+   (block
+    (call $print
+     (i32.const 3)
+    )
+    (return)
+   )
+  )
+ )
+)