[PATCH] [SeparateConstOffsetFromGEP] garbage-collect intermediate instructions

[Jingyue Wu]

Hi meheff,

so that we needn't run DCE after this pass.

http://reviews.llvm.org/D9096

Files:
  lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
  test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep-and-gvn.ll
  test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll

Index: lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
===================================================================
--- lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
+++ lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
@@ -167,6 +167,7 @@
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
 #include "llvm/IR/IRBuilder.h"
@@ -198,9 +199,12 @@
   /// Extracts a constant offset from the given GEP index. It returns the
   /// new index representing the remainder (equal to the original index minus
   /// the constant offset), or nullptr if we cannot extract a constant offset.
-  /// \p Idx    The given GEP index
-  /// \p GEP    The given GEP
-   static Value *Extract(Value *Idx, GetElementPtrInst *GEP);
+  /// \p Idx The given GEP index
+  /// \p GEP The given GEP
+  /// \p UserChainTail Outputs the tail of UserChain so that we can
+  ///                  garbage-collect unused instructions in UserChain.
+   static Value *Extract(Value *Idx, GetElementPtrInst *GEP,
+                         User *&UserChainTail);
   /// Looks for a constant offset from the given GEP index without extracting
   /// it. It returns the numeric value of the extracted constant offset (0 if
   /// failed). The meaning of the arguments are the same as Extract.
@@ -631,16 +635,21 @@
   return BO;
 }
 
-Value *ConstantOffsetExtractor::Extract(Value *Idx, GetElementPtrInst *GEP) {
+Value *ConstantOffsetExtractor::Extract(Value *Idx, GetElementPtrInst *GEP,
+                                        User *&UserChainTail) {
   ConstantOffsetExtractor Extractor(GEP);
   // Find a non-zero constant offset first.
   APInt ConstantOffset =
       Extractor.find(Idx, /* SignExtended */ false, /* ZeroExtended */ false,
                      GEP->isInBounds());
-  if (ConstantOffset == 0)
+  if (ConstantOffset == 0) {
+    UserChainTail = nullptr;
     return nullptr;
+  }
   // Separates the constant offset from the GEP index.
-  return Extractor.rebuildWithoutConstOffset();
+  Value *IdxWithoutConstOffset = Extractor.rebuildWithoutConstOffset();
+  UserChainTail = Extractor.UserChain.back();
+  return IdxWithoutConstOffset;
 }
 
 int64_t ConstantOffsetExtractor::Find(Value *Idx, GetElementPtrInst *GEP) {
@@ -869,9 +878,17 @@
     if (isa<SequentialType>(*GTI)) {
       // Splits this GEP index into a variadic part and a constant offset, and
       // uses the variadic part as the new index.
-      Value *NewIdx = ConstantOffsetExtractor::Extract(GEP->getOperand(I), GEP);
+      Value *OldIdx = GEP->getOperand(I);
+      User *UserChainTail;
+      Value *NewIdx =
+          ConstantOffsetExtractor::Extract(OldIdx, GEP, UserChainTail);
       if (NewIdx != nullptr) {
+        // Switches to the index with the constant offset removed.
         GEP->setOperand(I, NewIdx);
+        // After switching to the new index, we can garbage-collect UserChain
+        // and the old index if they are not used.
+        RecursivelyDeleteTriviallyDeadInstructions(UserChainTail);
+        RecursivelyDeleteTriviallyDeadInstructions(OldIdx);
       }
     }
   }
Index: test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep-and-gvn.ll
===================================================================
--- test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep-and-gvn.ll
+++ test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep-and-gvn.ll
@@ -1,5 +1,5 @@
 ; RUN: llc < %s -march=nvptx64 -mcpu=sm_20 | FileCheck %s --check-prefix=PTX
-; RUN: opt < %s -S -separate-const-offset-from-gep -gvn -dce | FileCheck %s --check-prefix=IR
+; RUN: opt < %s -S -separate-const-offset-from-gep -gvn | FileCheck %s --check-prefix=IR
 
 ; Verifies the SeparateConstOffsetFromGEP pass.
 ; The following code computes
Index: test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll
===================================================================
--- test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll
+++ test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll
@@ -1,4 +1,4 @@
-; RUN: opt < %s -separate-const-offset-from-gep -dce -S | FileCheck %s
+; RUN: opt < %s -separate-const-offset-from-gep -S | FileCheck %s
 
 ; Several unit tests for -separate-const-offset-from-gep. The transformation
 ; heavily relies on TargetTransformInfo, so we put these tests under

EMAIL PREFERENCES
  http://reviews.llvm.org/settings/panel/emailpreferences/
-------------- next part --------------
A non-text attachment was scrubbed...
Name: D9096.23991.patch
Type: text/x-patch
Size: 4503 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20150419/1cb02c71/attachment.bin>