Verify flat IR where it is expected, and give a nice error (#2009)

Fixes #2007 #2008

1 files changed, 4 insertions, 39 deletions

diff --git a/src/passes/Flatten.cpp b/src/passes/Flatten.cpp
index 61fc60b2b..df6be947d 100644
--- a/src/passes/Flatten.cpp
+++ b/src/passes/Flatten.cpp
@@ -15,39 +15,7 @@
  */
 
 //
-// Flattens code, removing nesting.e.g. an if return value would be
-// converted to a local
-//
-//  (i32.add
-//    (if (..condition..)
-//      (..if true..)
-//      (..if false..)
-//    )
-//    (i32.const 1)
-//  )
-// =>
-//  (if (..condition..)
-//    (local.set $temp
-//      (..if true..)
-//    )
-//    (local.set $temp
-//      (..if false..)
-//    )
-//  )
-//  (i32.add
-//    (local.get $temp)
-//    (i32.const 1)
-//  )
-//
-// Formally, this pass flattens in the precise sense of
-// making the AST have these properties:
-//
-//  1. The operands of an instruction must be a local.get or a const.
-//     anything else is written to a local earlier.
-//  2. Disallow block, loop, and if return values, i.e., do not use
-//     control flow to pass around values.
-//  3. Disallow local.tee, setting a local is always done in a local.set
-//     on a non-nested-expression location.
+// Flattens code into "Flat IR" form. See ir/flat.h.
 //
 
 #include <wasm.h>
@@ -55,6 +23,7 @@
 #include <wasm-builder.h>
 #include <ir/branch-utils.h>
 #include <ir/effects.h>
+#include <ir/flat.h>
 #include <ir/utils.h>
 
 namespace wasm {
@@ -89,7 +58,7 @@ struct Flatten : public WalkerPass<ExpressionStackWalker<Flatten, UnifiedExpress
     std::vector<Expression*> ourPreludes;
     Builder builder(*getModule());
 
-    if (isControlFlowStructure(curr)) {
+    if (Flat::isControlFlowStructure(curr)) {
       // handle control flow explicitly. our children do not have control flow,
       // but they do have preludes which we need to set up in the right place
       assert(preludes.find(curr) == preludes.end()); // no one should have given us preludes, they are on the children
@@ -275,7 +244,7 @@ struct Flatten : public WalkerPass<ExpressionStackWalker<Flatten, UnifiedExpress
     // next, finish up: migrate our preludes if we can
     if (!ourPreludes.empty()) {
       auto* parent = getParent();
-      if (parent && !isControlFlowStructure(parent)) {
+      if (parent && !Flat::isControlFlowStructure(parent)) {
         auto& parentPreludes = preludes[parent];
         for (auto* prelude : ourPreludes) {
           parentPreludes.push_back(prelude);
@@ -298,10 +267,6 @@ struct Flatten : public WalkerPass<ExpressionStackWalker<Flatten, UnifiedExpress
   }
 
 private:
-  bool isControlFlowStructure(Expression* curr) {
-    return curr->is<Block>() || curr->is<If>() || curr->is<Loop>();
-  }
-
   // gets an expression, either by itself, or in a block with its
   // preludes (which we use up) before it
   Expression* getPreludesWithExpression(Expression* curr) {