Fix a bug in DemoteRegToStack where a reload instruction was inserted into the

wrong basic block.

This would happen when the result of an invoke was used by a phi instruction
in the invoke's normal destination block. An instruction to reload the invoke's
value would get inserted before the critical edge was split and a new basic
block (which is the correct insertion point for the reload) was created. This
commit fixes the bug by splitting the critical edge before all the reload
instructions are inserted.

Also, hoist up the code which computes the insertion point to the only place
that need that computation.

rdar://problem/15978721

llvm-svn: 228566

1 files changed, 16 insertions, 18 deletions

diff --git a/llvm/lib/Transforms/Utils/DemoteRegToStack.cpp b/llvm/lib/Transforms/Utils/DemoteRegToStack.cpp
index 9972b22..003da58ee 100644
--- a/llvm/lib/Transforms/Utils/DemoteRegToStack.cpp
+++ b/llvm/lib/Transforms/Utils/DemoteRegToStack.cpp
@@ -39,6 +39,19 @@ AllocaInst *llvm::DemoteRegToStack(Instruction &I, bool VolatileLoads,
                           F->getEntryBlock().begin());
   }
 
+  // We cannot demote invoke instructions to the stack if their normal edge
+  // is critical. Therefore, split the critical edge and create a basic block
+  // into which the store can be inserted.
+  if (InvokeInst *II = dyn_cast<InvokeInst>(&I)) {
+    if (!II->getNormalDest()->getSinglePredecessor()) {
+      unsigned SuccNum = GetSuccessorNumber(II->getParent(), II->getNormalDest());
+      assert(isCriticalEdge(II, SuccNum) && "Expected a critical edge!");
+      BasicBlock *BB = SplitCriticalEdge(II, SuccNum);
+      assert(BB && "Unable to split critical edge.");
+      (void)BB;
+    }
+  }
+
   // Change all of the users of the instruction to read from the stack slot.
   while (!I.use_empty()) {
     Instruction *U = cast<Instruction>(I.user_back());
@@ -71,7 +84,6 @@ AllocaInst *llvm::DemoteRegToStack(Instruction &I, bool VolatileLoads,
     }
   }
 
-
   // Insert stores of the computed value into the stack slot. We have to be
   // careful if I is an invoke instruction, because we can't insert the store
   // AFTER the terminator instruction.
@@ -79,27 +91,13 @@ AllocaInst *llvm::DemoteRegToStack(Instruction &I, bool VolatileLoads,
   if (!isa<TerminatorInst>(I)) {
     InsertPt = &I;
     ++InsertPt;
+    for (; isa<PHINode>(InsertPt) || isa<LandingPadInst>(InsertPt); ++InsertPt)
+      /* empty */;   // Don't insert before PHI nodes or landingpad instrs.
   } else {
     InvokeInst &II = cast<InvokeInst>(I);
-    if (II.getNormalDest()->getSinglePredecessor())
-      InsertPt = II.getNormalDest()->getFirstInsertionPt();
-    else {
-      // We cannot demote invoke instructions to the stack if their normal edge
-      // is critical.  Therefore, split the critical edge and insert the store
-      // in the newly created basic block.
-      unsigned SuccNum = GetSuccessorNumber(I.getParent(), II.getNormalDest());
-      TerminatorInst *TI = &cast<TerminatorInst>(I);
-      assert (isCriticalEdge(TI, SuccNum) &&
-              "Expected a critical edge!");
-      BasicBlock *BB = SplitCriticalEdge(TI, SuccNum);
-      assert (BB && "Unable to split critical edge.");
-      InsertPt = BB->getFirstInsertionPt();
-    }
+    InsertPt = II.getNormalDest()->getFirstInsertionPt();
   }
 
-  for (; isa<PHINode>(InsertPt) || isa<LandingPadInst>(InsertPt); ++InsertPt)
-    /* empty */;   // Don't insert before PHI nodes or landingpad instrs.
-
   new StoreInst(&I, Slot, InsertPt);
   return Slot;
 }