[llvm] r293661 - [Instcombine] Combine consecutive identical fences

[Davide Italiano via llvm-commits]

Author: davide
Date: Tue Jan 31 12:09:05 2017
New Revision: 293661

URL: http://llvm.org/viewvc/llvm-project?rev=293661&view=rev
Log:
[Instcombine] Combine consecutive identical fences

Differential Revision:  https://reviews.llvm.org/D29314

Added:
    llvm/trunk/test/Transforms/InstCombine/consecutive-fences.ll
Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
    llvm/trunk/lib/Transforms/InstCombine/InstCombineInternal.h

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp?rev=293661&r1=293660&r2=293661&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp Tue Jan 31 12:09:05 2017
@@ -3268,6 +3268,15 @@ Instruction *InstCombiner::visitCallInst
   return visitCallSite(II);
 }
 
+// Fence instruction simplification
+Instruction *InstCombiner::visitFenceInst(FenceInst &FI) {
+  // Remove identical consecutive fences.
+  if (auto *NFI = dyn_cast<FenceInst>(FI.getNextNode()))
+    if (FI.isIdenticalTo(NFI))
+      return eraseInstFromFunction(FI);
+  return nullptr;
+}
+
 // InvokeInst simplification
 //
 Instruction *InstCombiner::visitInvokeInst(InvokeInst &II) {

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineInternal.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineInternal.h?rev=293661&r1=293660&r2=293661&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineInternal.h (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineInternal.h Tue Jan 31 12:09:05 2017
@@ -289,6 +289,7 @@ public:
   Instruction *visitLoadInst(LoadInst &LI);
   Instruction *visitStoreInst(StoreInst &SI);
   Instruction *visitBranchInst(BranchInst &BI);
+  Instruction *visitFenceInst(FenceInst &FI);
   Instruction *visitSwitchInst(SwitchInst &SI);
   Instruction *visitReturnInst(ReturnInst &RI);
   Instruction *visitInsertValueInst(InsertValueInst &IV);

Added: llvm/trunk/test/Transforms/InstCombine/consecutive-fences.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/consecutive-fences.ll?rev=293661&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/consecutive-fences.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/consecutive-fences.ll Tue Jan 31 12:09:05 2017
@@ -0,0 +1,47 @@
+; RUN: opt -instcombine -S %s | FileCheck %s
+
+; Make sure we collapse the fences in this case
+
+; CHECK-LABEL: define void @tinkywinky
+; CHECK-NEXT:   fence seq_cst
+; CHECK-NEXT:   fence singlethread acquire
+; CHECK-NEXT:   ret void
+; CHECK-NEXT: }
+
+define void @tinkywinky() {
+  fence seq_cst
+  fence seq_cst
+  fence seq_cst
+  fence singlethread acquire
+  fence singlethread acquire
+  fence singlethread acquire
+  ret void
+}
+
+; CHECK-LABEL: define void @dipsy
+; CHECK-NEXT:   fence seq_cst
+; CHECK-NEXT:   fence singlethread seq_cst
+; CHECK-NEXT:   ret void
+; CHECK-NEXT: }
+
+define void @dipsy() {
+  fence seq_cst
+  fence singlethread seq_cst
+  ret void
+}
+
+; CHECK-LABEL: define void @patatino
+; CHECK-NEXT:   fence acquire
+; CHECK-NEXT:   fence seq_cst
+; CHECK-NEXT:   fence acquire
+; CHECK-NEXT:   fence seq_cst
+; CHECK-NEXT:   ret void
+; CHECK-NEXT: }
+
+define void @patatino() {
+  fence acquire
+  fence seq_cst
+  fence acquire
+  fence seq_cst
+  ret void
+}