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

[Chris Lattner]

Changes in directory llvm/lib/Transforms/Scalar:

SimplifyCFG.cpp updated: 1.11 -> 1.12
---
Log message:

Turn store -> null/undef into the LLVM unreachable instruction!  This simple
change hacks off 10K of bytecode from perlbmk (.5%) even though the front-end
is not generating them yet and we are not optimizing the resultant code.  
This isn't too bad.


---
Diffs of the changes:  (+27 -0)

Index: llvm/lib/Transforms/Scalar/SimplifyCFG.cpp
diff -u llvm/lib/Transforms/Scalar/SimplifyCFG.cpp:1.11 llvm/lib/Transforms/Scalar/SimplifyCFG.cpp:1.12
--- llvm/lib/Transforms/Scalar/SimplifyCFG.cpp:1.11	Wed Sep  1 17:55:36 2004
+++ llvm/lib/Transforms/Scalar/SimplifyCFG.cpp	Sun Oct 17 22:00:50 2004
@@ -20,6 +20,8 @@
 
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Constants.h"
+#include "llvm/Instructions.h"
 #include "llvm/Module.h"
 #include "llvm/Support/CFG.h"
 #include "llvm/Pass.h"
@@ -45,6 +47,31 @@
   if (Reachable.count(BB)) return false;
   Reachable.insert(BB);
 
+  // Do a quick scan of the basic block, turning any obviously unreachable
+  // instructions into LLVM unreachable insts.  The instruction combining pass
+  // canonnicalizes unreachable insts into stores to null or undef.
+  for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E; ++BBI)
+    if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
+      if (isa<ConstantPointerNull>(SI->getOperand(1)) ||
+          isa<UndefValue>(SI->getOperand(1))) {
+        // Loop over all of the successors, removing BB's entry from any PHI
+        // nodes.
+        for (succ_iterator I = succ_begin(BB), SE = succ_end(BB); I != SE; ++I)
+          (*I)->removePredecessor(BB);
+
+        new UnreachableInst(SI);
+        std::cerr << "Inserted UNREACHABLE instruction!\n";
+
+        // All instructions after this are dead.
+        for (; BBI != E; ) {
+          if (!BBI->use_empty())
+            BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
+          BB->getInstList().erase(BBI++);
+        }
+        break;
+      }
+
+
   bool Changed = ConstantFoldTerminator(BB);
   for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
     MarkAliveBlocks(*SI, Reachable);