[PATCH] D15931: [LoopUnswitch] Create a PHINode for the original landingpad only if it has some uses

[Chen Li via llvm-commits]

chenli created this revision.
chenli added a reviewer: reames.
chenli added a subscriber: llvm-commits.

This patch adds a check in UnswitchNontrivialCondition to see if the original landingpad instruction has any uses. If not, we don't need to create a PHINode for it after SplitExitEdges. Please refer to D15835 for the motivation.

http://reviews.llvm.org/D15931

Files:
  lib/Transforms/Scalar/LoopUnswitch.cpp
  test/Transforms/LoopUnswitch/token.ll

Index: test/Transforms/LoopUnswitch/token.ll
===================================================================
--- /dev/null
+++ test/Transforms/LoopUnswitch/token.ll
@@ -0,0 +1,43 @@
+; RUN: opt < %s -loop-unswitch -S 2>&1 | FileCheck %s
+
+define void @test1(i1 %cond) personality i32 ()* @"dummy_personality" {
+entry:
+  br label %for.cond
+
+for.cond:
+  call void @dummy_call()           
+  br i1 %cond, label %for.body, label %for.end
+  
+for.body:                              
+  invoke void @dummy_invoke()
+          to label %invoke.cont unwind label %lpad
+
+invoke.cont:                                      
+  br label %for.inc
+
+lpad:                                             
+  %a = landingpad token
+          cleanup
+  unreachable
+  
+for.inc:                                          
+  br label %for.cond
+
+for.end:                                          
+  ret void
+}
+
+; CHECK: lpad.us-lcssa.us:                                 ; preds = %for.body.us
+; CHECK-NEXT:  %lpad.us-lcssa1.us = landingpad token
+
+; CHECK: lpad.us-lcssa:                                    ; preds = %for.body
+; CHECK-NEXT:  %lpad.us-lcssa1 = landingpad token
+
+; CHECK: lpad:                                             ; preds = %lpad.us-lcssa.us, %lpad.us-lcssa
+; CHECK-NOT: phi token
+
+declare void @dummy_call()
+
+declare void @dummy_invoke()
+
+declare i32 @"dummy_personality"()
Index: lib/Transforms/Scalar/LoopUnswitch.cpp
===================================================================
--- lib/Transforms/Scalar/LoopUnswitch.cpp
+++ lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -1060,15 +1060,21 @@
     }
 
     if (LandingPadInst *LPad = NewExit->getLandingPadInst()) {
-      PHINode *PN = PHINode::Create(LPad->getType(), 0, "",
-                                    &*ExitSucc->getFirstInsertionPt());
-
-      for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc);
-           I != E; ++I) {
-        BasicBlock *BB = *I;
-        LandingPadInst *LPI = BB->getLandingPadInst();
-        LPI->replaceAllUsesWith(PN);
-        PN->addIncoming(LPI, BB);
+      auto *OriginalLPad = ExitBlocks[i]->getLandingPadInst();
+      if (!OriginalLPad->use_empty()) {
+        assert(!LPad->getType()->isTokenTy() &&
+               "Loop unswitch cannot be applied if LPad is token type. "
+               "Otherwise an invalid PHINode of token type would be created.");
+        PHINode *PN = PHINode::Create(LPad->getType(), 0, "",
+                                      &*ExitSucc->getFirstInsertionPt());
+
+        for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc);
+             I != E; ++I) {
+          BasicBlock *BB = *I;
+          LandingPadInst *LPI = BB->getLandingPadInst();
+          LPI->replaceAllUsesWith(PN);
+          PN->addIncoming(LPI, BB);
+        }
       }
     }
   }


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