[PATCH] CodeGen: Add IntegerDivisionPass

[Michael Ilseman]

+bool IntegerDivision::runOnFunction(Function &F) {
+
+  if (TM)
+    TLI = TM->getSubtargetImpl()->getTargetLowering();
+
+  for (Function::iterator BBI = F.begin(), BBE = F.end(); BBI != BBE; ++BBI) {
+       BasicBlock *BB = BBI;
+    for (BasicBlock::iterator II = BB->begin(), IE = BB->end(); II != IE; ++II) {
+        Instruction *I = II;
+        if (visit(*I)) {
+          BBI = F.begin();
+          break;
+        }
+    }
+  }
+
+  return false;
+}

You should have a bool for whether the code changed, and return that[1]. It’s probably worth building up a worklist of basic blocks up front, to avoid the repeated visiting of already-handled blocks. Also, we know that many of the blocks that are generated from division-expansion would not themselves have rem or div in them.


+bool IntegerDivision::shouldExpandDivRem(const BinaryOperator &I) {
+  return TLI && TLI->shouldExpandDivRemInIR(I);
+}

You could do the TLI-is-not-null check in runOnFunction, which is a good place to bail early. Thereafter you can have an assert. I don’t know who would be using this pass normally, though.

Otherwise the patch LGTM. What is your use case of wanting a full-fledged pass for this? If you have other codegen-prepare-like things to do to the IR, it seems suboptimal to do a pass over every instruction just for div/rem, at least from a low-latency compilation time perspective.


[1] http://llvm.org/docs/WritingAnLLVMPass.html#the-runonfunction-method






On Sep 24, 2014, at 10:06 AM, Tom Stellard <tom at stellard.net> wrote:

> On Tue, Sep 23, 2014 at 01:57:23PM -0700, Michael Ilseman wrote:
>> 
>>> On Sep 23, 2014, at 12:48 PM, Tom Stellard <thomas.stellard at amd.com> wrote:
>>> 
>>> This pass will expand unsupported div/rem instructions based on
>>> the result of the newly added TargetLowering::shouldExpandDivRemInIR().
>>> ---
>>> 
>>> A future commit will enable this pass for the R600 backend and add tests.
>>> 
>>> include/llvm/CodeGen/Passes.h        |   6 ++
>>> include/llvm/InitializePasses.h      |   1 +
>>> include/llvm/Target/TargetLowering.h |   6 ++
>>> lib/CodeGen/CMakeLists.txt           |   1 +
>>> lib/CodeGen/IntegerDivisionPass.cpp  | 124 +++++++++++++++++++++++++++++++++++
>>> 5 files changed, 138 insertions(+)
>>> create mode 100644 lib/CodeGen/IntegerDivisionPass.cpp
>>> 
>>> diff --git a/include/llvm/CodeGen/Passes.h b/include/llvm/CodeGen/Passes.h
>>> index 31fba89..3fedd5a 100644
>>> --- a/include/llvm/CodeGen/Passes.h
>>> +++ b/include/llvm/CodeGen/Passes.h
>>> @@ -376,6 +376,9 @@ namespace llvm {
>>>  /// load-linked/store-conditional loops.
>>>  extern char &AtomicExpandID;
>>> 
>>> +  /// Lowers unsupported integer division.
>>> +  extern char &IntegerDivisionID;
>>> +
>>>  /// MachineLoopInfo - This pass is a loop analysis pass.
>>>  extern char &MachineLoopInfoID;
>>> 
>>> @@ -598,6 +601,9 @@ namespace llvm {
>>> 
>>>  /// createJumpInstrTables - This pass creates jump-instruction tables.
>>>  ModulePass *createJumpInstrTablesPass();
>>> +
>>> +  /// Lower unsupported integer division
>>> +  FunctionPass *createIntegerDivisionPass(const TargetMachine *TM);
>>> } // End llvm namespace
>>> 
>>> /// This initializer registers TargetMachine constructor, so the pass being
>>> diff --git a/include/llvm/InitializePasses.h b/include/llvm/InitializePasses.h
>>> index 2964798..99f7ab5 100644
>>> --- a/include/llvm/InitializePasses.h
>>> +++ b/include/llvm/InitializePasses.h
>>> @@ -146,6 +146,7 @@ void initializeInlineCostAnalysisPass(PassRegistry&);
>>> void initializeInstCombinerPass(PassRegistry&);
>>> void initializeInstCountPass(PassRegistry&);
>>> void initializeInstNamerPass(PassRegistry&);
>>> +void initializeIntegerDivisionPass(PassRegistry&);
>>> void initializeInternalizePassPass(PassRegistry&);
>>> void initializeIntervalPartitionPass(PassRegistry&);
>>> void initializeJumpInstrTableInfoPass(PassRegistry&);
>>> diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
>>> index 0a72225..245df33 100644
>>> --- a/include/llvm/Target/TargetLowering.h
>>> +++ b/include/llvm/Target/TargetLowering.h
>>> @@ -1000,6 +1000,12 @@ public:
>>>    return false;
>>>  }
>>> 
>>> +  /// Returns true if the instruction should be expanded by the IR-level
>>> +  /// IntegerDivision pass.
>>> +  virtual bool shouldExpandDivRemInIR(const BinaryOperator &I) const {
>>> +    return false;
>>> +  }
>>> +
>>>  //===--------------------------------------------------------------------===//
>>>  // TargetLowering Configuration Methods - These methods should be invoked by
>>>  // the derived class constructor to configure this object for the target.
>>> diff --git a/lib/CodeGen/CMakeLists.txt b/lib/CodeGen/CMakeLists.txt
>>> index 0e06ed0..d002f47 100644
>>> --- a/lib/CodeGen/CMakeLists.txt
>>> +++ b/lib/CodeGen/CMakeLists.txt
>>> @@ -25,6 +25,7 @@ add_llvm_library(LLVMCodeGen
>>>  GlobalMerge.cpp
>>>  IfConversion.cpp
>>>  InlineSpiller.cpp
>>> +  IntegerDivisionPass.cpp
>>>  InterferenceCache.cpp
>>>  IntrinsicLowering.cpp
>>>  JumpInstrTables.cpp
>>> diff --git a/lib/CodeGen/IntegerDivisionPass.cpp b/lib/CodeGen/IntegerDivisionPass.cpp
>>> new file mode 100644
>>> index 0000000..b198a1f
>>> --- /dev/null
>>> +++ b/lib/CodeGen/IntegerDivisionPass.cpp
>>> @@ -0,0 +1,124 @@
>>> +//===-- IntegerDivisionPass.cpp - Expand div/mod instructions -------------===//
>>> +//
>>> +//                     The LLVM Compiler Infrastructure
>>> +//
>>> +// This file is distributed under the University of Illinois Open Source
>>> +// License. See LICENSE.TXT for details.
>>> +//
>>> +//===----------------------------------------------------------------------===//
>>> +//
>>> +/// \file
>>> +//===----------------------------------------------------------------------===//
>>> +
>>> +#include "llvm/CodeGen/Passes.h"
>>> +#include "llvm/IR/IRBuilder.h"
>>> +#include "llvm/IR/InstVisitor.h"
>>> +#include "llvm/Target/TargetLowering.h"
>>> +#include "llvm/Target/TargetMachine.h"
>>> +#include "llvm/Target/TargetSubtargetInfo.h"
>>> +#include "llvm/Transforms/Utils/IntegerDivision.h"
>>> +using namespace llvm;
>>> +
>>> +#define DEBUG_TYPE "integer-division"
>>> +
>>> +namespace {
>>> +
>>> +class IntegerDivision : public FunctionPass,
>>> +                        public InstVisitor<IntegerDivision, bool> {
>>> +
>>> +  const TargetMachine *TM;
>>> +  const TargetLowering *TLI;
>>> +
>>> +  std::vector<BinaryOperator *> Divs;
>>> +  std::vector<BinaryOperator *> Rems;
>>> +
>> 
>> As far as I can tell from the patch, these vectors are not used. What is their intent?
>> 
> 
> These are leftover from a previous version of the patch.  Here is an updated
> patch with them removed.
> 
> -Tom
> <0001-CodeGen-Add-IntegerDivisionPass.patch>

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