[llvm-commits] CVS: llvm/lib/Transforms/Utils/SimplifyCFG.cpp

[Chris Lattner]

Changes in directory llvm/lib/Transforms/Utils:

SimplifyCFG.cpp updated: 1.72 -> 1.73
---
Log message:

This code was very close, but not quite right.  It did not take into
consideration the case where a reference in an unreachable block could 
occur.  This fixes Transforms/SimplifyCFG/2005-08-01-PHIUpdateFail.ll,
something I ran into while bugpoint'ing another pass.


---
Diffs of the changes:  (+10 -3)

 SimplifyCFG.cpp |   13 ++++++++++---
 1 files changed, 10 insertions(+), 3 deletions(-)


Index: llvm/lib/Transforms/Utils/SimplifyCFG.cpp
diff -u llvm/lib/Transforms/Utils/SimplifyCFG.cpp:1.72 llvm/lib/Transforms/Utils/SimplifyCFG.cpp:1.73
--- llvm/lib/Transforms/Utils/SimplifyCFG.cpp:1.72	Thu Jun 16 20:45:53 2005
+++ llvm/lib/Transforms/Utils/SimplifyCFG.cpp	Mon Aug  1 22:24:05 2005
@@ -894,9 +894,16 @@
           // Move all PHI nodes in BB to Succ if they are alive, otherwise
           // delete them.
           while (PHINode *PN = dyn_cast<PHINode>(&BB->front()))
-            if (PN->use_empty())
-              BB->getInstList().erase(BB->begin());  // Nuke instruction.
-            else {
+            if (PN->use_empty() || Succ->getSinglePredecessor() == 0) {
+              // We can only move the PHI node into Succ if BB dominates Succ.
+              // Since BB only has a single successor (Succ), the PHI nodes
+              // will dominate Succ, unless Succ has multiple predecessors.  In
+              // this case, the PHIs are either dead, or have references in dead
+              // blocks.  In either case, we can just remove them.
+              if (!PN->use_empty())   // Uses in dead block?
+                PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
+              PN->eraseFromParent();  // Nuke instruction.
+            } else {
               // The instruction is alive, so this means that Succ must have
               // *ONLY* had BB as a predecessor, and the PHI node is still valid
               // now.  Simply move it into Succ, because we know that BB