LICM does get dead instructions input to it. Instead of sinking them

out of loops, just delete them.

llvm-svn: 112451

2 files changed, 26 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index 5f156dba725..aa842e3183b 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -43,6 +43,7 @@
 #include "llvm/Analysis/AliasSetTracker.h"
 #include "llvm/Analysis/Dominators.h"
 #include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Transforms/Utils/SSAUpdater.h"
 #include "llvm/Support/CFG.h"
 #include "llvm/Support/CommandLine.h"
@@ -299,7 +300,7 @@ void LICM::SinkRegion(DomTreeNode *N) {
   // If this subregion is not in the top level loop at all, exit.
   if (!CurLoop->contains(BB)) return;
 
-  // We are processing blocks in reverse dfo, so process children first...
+  // We are processing blocks in reverse dfo, so process children first.
   const std::vector<DomTreeNode*> &Children = N->getChildren();
   for (unsigned i = 0, e = Children.size(); i != e; ++i)
     SinkRegion(Children[i]);
@@ -310,6 +311,16 @@ void LICM::SinkRegion(DomTreeNode *N) {
 
   for (BasicBlock::iterator II = BB->end(); II != BB->begin(); ) {
     Instruction &I = *--II;
+    
+    // If the instruction is dead, we would try to sink it because it isn't used
+    // in the loop, instead, just delete it.
+    if (isInstructionTriviallyDead(&I)) {
+      ++II;
+      CurAST->deleteValue(&I);
+      I.eraseFromParent();
+      Changed = true;
+      continue;
+    }
 
     // Check to see if we can sink this instruction to the exit blocks
     // of the loop.  We can do this if the all users of the instruction are
diff --git a/llvm/test/Transforms/LICM/sinking.ll b/llvm/test/Transforms/LICM/sinking.ll
index 11112eb7444..68e4b64bf9b 100644
--- a/llvm/test/Transforms/LICM/sinking.ll
+++ b/llvm/test/Transforms/LICM/sinking.ll
@@ -233,3 +233,17 @@ Out:		; preds = %Loop
 ; CHECK-NEXT:  ret i32 %tmp.6
 }
 
+; Should delete, not sink, dead instructions.
+define void @test11() {
+	br label %Loop
+Loop:
+	%dead = getelementptr %Ty* @X2, i64 0, i32 0
+	br i1 false, label %Loop, label %Out
+Out:
+	ret void
+; CHECK: @test11
+; CHECK:     Out:
+; CHECK-NEXT:  ret void
+}
+
+