[llvm] r358600 - [InstCombine] Factor out unreachable inst idiom creation [NFC]

[Philip Reames via llvm-commits]

Author: reames
Date: Wed Apr 17 10:37:58 2019
New Revision: 358600

URL: http://llvm.org/viewvc/llvm-project?rev=358600&view=rev
Log:
[InstCombine] Factor out unreachable inst idiom creation [NFC]

In InstCombine, we use an idiom of "store i1 true, i1 undef" to indicate we've found a path which we've proven unreachable.  We can't actually insert the unreachable instruction since that would require changing the CFG.  We leave that to simplifycfg later.

This just factors out that idiom creation so we don't duplicate the same mostly undocument idiom creation in multiple places.


Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
    llvm/trunk/lib/Transforms/InstCombine/InstCombineInternal.h
    llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp?rev=358600&r1=358599&r2=358600&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp Wed Apr 17 10:37:58 2019
@@ -4324,9 +4324,7 @@ Instruction *InstCombiner::visitCallBase
         // variety of reasons (e.g. it may be written in assembly).
         !CalleeF->isDeclaration()) {
       Instruction *OldCall = &Call;
-      new StoreInst(ConstantInt::getTrue(Callee->getContext()),
-                UndefValue::get(Type::getInt1PtrTy(Callee->getContext())),
-                                  OldCall);
+      CreateNonTerminatorUnreachable(OldCall);
       // If OldCall does not return void then replaceAllUsesWith undef.
       // This allows ValueHandlers and custom metadata to adjust itself.
       if (!OldCall->getType()->isVoidTy())
@@ -4356,13 +4354,8 @@ Instruction *InstCombiner::visitCallBase
       return nullptr;
     }
 
-    // This instruction is not reachable, just remove it.  We insert a store to
-    // undef so that we know that this code is not reachable, despite the fact
-    // that we can't modify the CFG here.
-    new StoreInst(ConstantInt::getTrue(Callee->getContext()),
-                  UndefValue::get(Type::getInt1PtrTy(Callee->getContext())),
-                  &Call);
-
+    // This instruction is not reachable, just remove it.
+    CreateNonTerminatorUnreachable(&Call);
     return eraseInstFromFunction(Call);
   }
 

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineInternal.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineInternal.h?rev=358600&r1=358599&r2=358600&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineInternal.h (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineInternal.h Wed Apr 17 10:37:58 2019
@@ -656,6 +656,16 @@ public:
     return InsertValueInst::Create(Struct, Result, 0);
   }
 
+  /// Create and insert the idiom we use to indicate a block is unreachable
+  /// without having to rewrite the CFG from within InstCombine.
+  void CreateNonTerminatorUnreachable(Instruction *InsertAt) {
+    auto &Ctx = InsertAt->getContext();
+    new StoreInst(ConstantInt::getTrue(Ctx),
+                  UndefValue::get(Type::getInt1PtrTy(Ctx)),
+                  InsertAt);
+  }
+
+
   /// Combiner aware instruction erasure.
   ///
   /// When dealing with an instruction that has side effects or produces a void

Modified: llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp?rev=358600&r1=358599&r2=358600&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp Wed Apr 17 10:37:58 2019
@@ -2475,9 +2475,8 @@ Instruction *InstCombiner::visitFree(Cal
 
   // free undef -> unreachable.
   if (isa<UndefValue>(Op)) {
-    // Insert a new store to null because we cannot modify the CFG here.
-    Builder.CreateStore(ConstantInt::getTrue(FI.getContext()),
-                        UndefValue::get(Type::getInt1PtrTy(FI.getContext())));
+    // Leave a marker since we can't modify the CFG here.
+    CreateNonTerminatorUnreachable(&FI);
     return eraseInstFromFunction(FI);
   }