From 8a59de408a576ae41a16837bb82bae5b51aebca1 Mon Sep 17 00:00:00 2001
From: Alon Zakai <alonzakai@gmail.com>
Date: Sun, 23 Mar 2014 18:53:14 -0700
Subject: handle switches that reach phis appearing before them; fixes
 emscripen issue 2244

---
 lib/Target/JSBackend/ExpandI64.cpp | 31 ++++++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

diff --git a/lib/Target/JSBackend/ExpandI64.cpp b/lib/Target/JSBackend/ExpandI64.cpp
index e595594e41..9929033169 100644
--- a/lib/Target/JSBackend/ExpandI64.cpp
+++ b/lib/Target/JSBackend/ExpandI64.cpp
@@ -42,6 +42,7 @@
 #include "llvm/Target/TargetLibraryInfo.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include <map>
+#include <vector>
 
 #include "llvm/Support/raw_ostream.h"
 
@@ -54,6 +55,10 @@ using namespace llvm;
 
 namespace {
 
+  struct PhiBlockChange {
+    BasicBlock *DD, *SwitchBB, *NewBB;
+  };
+
   typedef SmallVector<Value*, 2> ChunksVec;
   typedef std::map<Value*, ChunksVec> SplitsMap;
 
@@ -69,6 +74,7 @@ namespace {
 
     SplitsMap Splits; // old illegal value to new insts
     PHIVec Phis;
+    std::vector<PhiBlockChange> PhiBlockChanges;
 
     // If the function has an illegal return or argument, create a legal version
     void ensureLegalFunc(Function *F);
@@ -890,13 +896,12 @@ bool ExpandI64::splitInst(Instruction *I) {
         // We used to go SwitchBB->DD, but now go SwitchBB->NewBB->DD, fix that like with BB above. However here we do not replace,
         // as the switch BB is still possible to arrive from - we can arrive at the default if either the lower bits were wrong (we
         // arrive from the switchBB) or from the NewBB if the high bits were wrong.
-        for (BasicBlock::iterator I = DD->begin(); I != DD->end(); ++I) {
-          PHINode *Phi = dyn_cast<PHINode>(I);
-          if (!Phi) break;
-          Phi->addIncoming(Phi->getIncomingValue(Phi->getBasicBlockIndex(SwitchBB)), NewBB);
-          // XXX note that we add a new i64 thing here. now the phi was already an i64 operation, and is being legalized anyhow, but we only notice the original inputs!
-          //     we seem to be safe for now due to order of operation (phis show up after switches, but FIXME
-        }
+        // We cannot do this here right now, as phis we encounter may be in the middle of processing (empty), so we queue these.
+        PhiBlockChange Change;
+        Change.DD = DD;
+        Change.SwitchBB = SwitchBB;
+        Change.NewBB = NewBB;
+        PhiBlockChanges.push_back(Change);
       }
       break;
     }
@@ -1091,6 +1096,18 @@ bool ExpandI64::runOnModule(Module &M) {
       PN->dropAllReferences();
     }
 
+    // Apply basic block changes to phis, now that phis are all processed
+    for (unsigned i = 0; i < PhiBlockChanges.size(); i++) {
+      PhiBlockChange &Change = PhiBlockChanges[i];
+      for (BasicBlock::iterator I = Change.DD->begin(); I != Change.DD->end(); ++I) {
+        PHINode *Phi = dyn_cast<PHINode>(I);
+        if (!Phi) break;
+        int Index = Phi->getBasicBlockIndex(Change.SwitchBB);
+        assert(Index >= 0);
+        Phi->addIncoming(Phi->getIncomingValue(Index), Change.NewBB);
+      }
+    }
+
     // Delete instructions which were replaced. We do this after the full walk
     // of the instructions so that all uses are replaced first.
     while (!Dead.empty()) {
-- 
cgit v1.2.3-18-g5258