[llvm-commits] [llvm] r164173 - in /llvm/trunk: include/llvm/Transforms/Utils/IntegerDivision.h lib/Transforms/Utils/CMakeLists.txt lib/Transforms/Utils/IntegerDivision.cpp
Alex Rosenberg
alexr at leftfield.org
Wed Sep 19 13:23:26 PDT 2012
On Sep 19, 2012, at 11:25 AM, Michael Ilseman wrote:
>> There are neither users nor tests of this code in the tree. That is a really bad state. This will bitrot immediately. Please write thorough tests for this if you want to keep it in the tree as a utility for out-of-tree projects. Other developers have no other way to exercise it.
>
> What do you think the best way to test a utility is? Should I make a new pass so that I can use the existing testing framework for opt?
A gtest unit test, perhaps? There already are some for Transforms/Utils code.
Since this is such a large amount of IR being output, perhaps it would be better to check in a well-commented .ll file that implements it and add build process to emit that as code. Given that infrastructure, we're well-positioned for other inline expansions like this and can provide better testing.
Alex
> On Sep 18, 2012, at 7:17 PM, Chandler Carruth <chandlerc at google.com> wrote:
>
>> I'm sad this didn't get any pre-commit review on the public mailing lists...
>>
>> On Tue, Sep 18, 2012 at 3:02 PM, Michael Ilseman <milseman at apple.com> wrote:
>> Author: milseman
>> Date: Tue Sep 18 17:02:40 2012
>> New Revision: 164173
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=164173&view=rev
>> Log:
>> New utility for expanding integer division for targets that don't support it.
>>
>> Implementation derived from compiler-rt's implementation of signed and unsigned integer division.
>>
>> There are neither users nor tests of this code in the tree. That is a really bad state. This will bitrot immediately. Please write thorough tests for this if you want to keep it in the tree as a utility for out-of-tree projects. Other developers have no other way to exercise it.
>>
>> Also:
>>
>> +namespace llvm {
>> +
>> + bool expandDivision(BinaryOperator* Div);
>>
>> Zero comments? No Doxygen? This hardly seems appropriate. I realize the external behavior is simple, but that doesn't mean it can go without documentation.
>>
>>
>> +
>> +} // End llvm namespace
>> +
>> +#endif
>>
>> Modified: llvm/trunk/lib/Transforms/Utils/CMakeLists.txt
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/CMakeLists.txt?rev=164173&r1=164172&r2=164173&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Utils/CMakeLists.txt (original)
>> +++ llvm/trunk/lib/Transforms/Utils/CMakeLists.txt Tue Sep 18 17:02:40 2012
>> @@ -11,6 +11,7 @@
>> DemoteRegToStack.cpp
>> InlineFunction.cpp
>> InstructionNamer.cpp
>> + IntegerDivision.cpp
>> LCSSA.cpp
>> Local.cpp
>> LoopSimplify.cpp
>>
>> Added: llvm/trunk/lib/Transforms/Utils/IntegerDivision.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/IntegerDivision.cpp?rev=164173&view=auto
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Utils/IntegerDivision.cpp (added)
>> +++ llvm/trunk/lib/Transforms/Utils/IntegerDivision.cpp Tue Sep 18 17:02:40 2012
>> @@ -0,0 +1,306 @@
>> +//===-- IntegerDivision.cpp - Expand integer division ---------------------===//
>> +//
>> +// The LLVM Compiler Infrastructure
>> +//
>> +// This file is distributed under the University of Illinois Open Source
>> +// License. See LICENSE.TXT for details.
>> +//
>> +//===----------------------------------------------------------------------===//
>> +//
>> +// This file contains an implementation of 32bit scalar integer division for
>> +// targets that don't have native support. It's largely derived from
>> +// compiler-rt's implementation of __udivsi3, but hand-tuned to reduce the
>> +// amount of control flow
>> +//
>> +//===----------------------------------------------------------------------===//
>> +
>> +#define DEBUG_TYPE "integer-division"
>> +#include "llvm/Function.h"
>> +#include "llvm/Instructions.h"
>> +#include "llvm/Intrinsics.h"
>> +#include "llvm/IRBuilder.h"
>> +#include "llvm/Transforms/Utils/IntegerDivision.h"
>> +
>> +using namespace llvm;
>> +
>> +// Generate code to divide two signed integers. Returns the quotient, rounded
>> +// towards 0. Builder's insert point should be pointing at the sdiv
>> +// instruction. This will generate a udiv in the process, and Builder's insert
>> +// point will be pointing at the udiv (if present, i.e. not folded), ready to be
>> +// expanded if the user wishes.
>> +static Value* GenerateSignedDivisionCode(Value* Dividend, Value* Divisor,
>> + IRBuilder<>& Builder) {
>> + // Implementation taken from compiler-rt's __divsi3
>> +
>> + ConstantInt* ThirtyOne = Builder.getInt32(31);
>>
>> The "*" are consistently in the wrong place. Also this doesn't follow the style guide's naming conventions. Also it should have a doxygen comment.
>>
>> +
>> + // ; %tmp = ashr i32 %dividend, 31
>> + // ; %tmp1 = ashr i32 %divisor, 31
>> + // ; %tmp2 = xor i32 %tmp, %dividend
>> + // ; %u_dvnd = sub nsw i32 %tmp2, %tmp
>> + // ; %tmp3 = xor i32 %tmp1, %divisor
>> + // ; %u_dvsr = sub nsw i32 %tmp3, %tmp1
>> + // ; %q_sgn = xor i32 %tmp1, %tmp
>> + // ; %q_mag = udiv i32 %u_dvnd, %u_dvsr
>> + // ; %tmp4 = xor i32 %q_mag, %q_sgn
>> + // ; %q = sub i32 %tmp4, %q_sgn
>> + Value* Tmp = Builder.CreateAShr(Dividend, ThirtyOne);
>> + Value* Tmp1 = Builder.CreateAShr(Divisor, ThirtyOne);
>> + Value* Tmp2 = Builder.CreateXor(Tmp, Dividend);
>> + Value* U_Dvnd = Builder.CreateSub(Tmp2, Tmp);
>>
>> You've given these variables terribly hard to read names when the length of name costs nothing. Could use use something more readable?
>>
>> Also, You've not given any names to the actual instructions being built, which will make reading the IR produced by this much harder.
>>
>> + Value* Tmp3 = Builder.CreateXor(Tmp1, Divisor);
>> + Value* U_Dvsr = Builder.CreateSub(Tmp3, Tmp1);
>> + Value* Q_Sgn = Builder.CreateXor(Tmp1, Tmp);
>> + Value* Q_Mag = Builder.CreateUDiv(U_Dvnd, U_Dvsr);
>> + Value* Tmp4 = Builder.CreateXor(Q_Mag, Q_Sgn);
>> + Value* Q = Builder.CreateSub(Tmp4, Q_Sgn);
>> +
>> + if (Instruction* UDiv = dyn_cast<Instruction>(Q_Mag))
>> + Builder.SetInsertPoint(UDiv);
>> +
>> + return Q;
>> +}
>> +
>> +// Generates code to divide two unsigned scalar 32-bit integers. Returns the
>> +// quotient, rounded towards 0. Builder's insert point should be pointing at the
>> +// udiv instruction.
>> +static Value* GenerateUnsignedDivisionCode(Value* Dividend, Value* Divisor,
>> + IRBuilder<>& Builder) {
>> + // The basic algorithm can be found in the compiler-rt project's
>> + // implementation of __udivsi3.c. Here, we do a lower-level IR based approach
>> + // that's been hand-tuned to lessen the amount of control flow involved.
>> +
>> + // Some helper values
>> + IntegerType* I32Ty = Builder.getInt32Ty();
>> +
>> + ConstantInt* Zero = Builder.getInt32(0);
>> + ConstantInt* One = Builder.getInt32(1);
>> + ConstantInt* ThirtyOne = Builder.getInt32(31);
>> + ConstantInt* NegOne = ConstantInt::getSigned(I32Ty, -1);
>> + ConstantInt* True = Builder.getTrue();
>> +
>> + BasicBlock* IBB = Builder.GetInsertBlock();
>> + Function* F = IBB->getParent();
>> + Function* CTLZi32 = Intrinsic::getDeclaration(F->getParent(), Intrinsic::ctlz,
>> + I32Ty);
>> +
>> + // Our CFG is going to look like:
>> + // +---------------------+
>> + // | special-cases |
>> + // | ... |
>> + // +---------------------+
>> + // | |
>> + // | +----------+
>> + // | | bb1 |
>> + // | | ... |
>> + // | +----------+
>> + // | | |
>> + // | | +------------+
>> + // | | | preheader |
>> + // | | | ... |
>> + // | | +------------+
>> + // | | |
>> + // | | | +---+
>> + // | | | | |
>> + // | | +------------+ |
>> + // | | | do-while | |
>> + // | | | ... | |
>> + // | | +------------+ |
>> + // | | | | |
>> + // | +-----------+ +---+
>> + // | | loop-exit |
>> + // | | ... |
>> + // | +-----------+
>> + // | |
>> + // +-------+
>> + // | ... |
>> + // | end |
>> + // +-------+
>> + BasicBlock* SpecialCases = Builder.GetInsertBlock();
>> + SpecialCases->setName(Twine(SpecialCases->getName(), "_udiv-special-cases"));
>> + BasicBlock* End = SpecialCases->splitBasicBlock(Builder.GetInsertPoint(),
>> + "udiv-end");
>> + BasicBlock* LoopExit = BasicBlock::Create(Builder.getContext(),
>> + "udiv-loop-exit", F, End);
>> + BasicBlock* DoWhile = BasicBlock::Create(Builder.getContext(),
>> + "udiv-do-while", F, End);
>> + BasicBlock* Preheader = BasicBlock::Create(Builder.getContext(),
>> + "udiv-preheader", F, End);
>> + BasicBlock* BB1 = BasicBlock::Create(Builder.getContext(),
>> + "udiv-bb1", F, End);
>> +
>> + // We'll be overwriting the terminator to insert our extra blocks
>> + SpecialCases->getTerminator()->eraseFromParent();
>> +
>> + // First off, check for special cases: dividend or divisor is zero, divisor
>> + // is greater than dividend, and divisor is 1.
>> + // ; special-cases:
>> + // ; %ret0_1 = icmp eq i32 %divisor, 0
>> + // ; %ret0_2 = icmp eq i32 %dividend, 0
>> + // ; %ret0_3 = or i1 %ret0_1, %ret0_2
>> + // ; %tmp0 = tail call i32 @llvm.ctlz.i32(i32 %divisor, i1 true)
>> + // ; %tmp1 = tail call i32 @llvm.ctlz.i32(i32 %dividend, i1 true)
>> + // ; %sr = sub nsw i32 %tmp0, %tmp1
>> + // ; %ret0_4 = icmp ugt i32 %sr, 31
>> + // ; %ret0 = or i1 %ret0_3, %ret0_4
>> + // ; %retDividend = icmp eq i32 %sr, 31
>> + // ; %retVal = select i1 %ret0, i32 0, i32 %dividend
>> + // ; %earlyRet = or i1 %ret0, %retDividend
>> + // ; br i1 %earlyRet, label %end, label %bb1
>> + Builder.SetInsertPoint(SpecialCases);
>> + Value* Ret0_1 = Builder.CreateICmpEQ(Divisor, Zero);
>> + Value* Ret0_2 = Builder.CreateICmpEQ(Dividend, Zero);
>> + Value* Ret0_3 = Builder.CreateOr(Ret0_1, Ret0_2);
>> + Value* Tmp0 = Builder.CreateCall2(CTLZi32, Divisor, True);
>> + Value* Tmp1 = Builder.CreateCall2(CTLZi32, Dividend, True);
>> + Value* SR = Builder.CreateSub(Tmp0, Tmp1);
>> + Value* Ret0_4 = Builder.CreateICmpUGT(SR, ThirtyOne);
>> + Value* Ret0 = Builder.CreateOr(Ret0_3, Ret0_4);
>> + Value* RetDividend = Builder.CreateICmpEQ(SR, ThirtyOne);
>> + Value* RetVal = Builder.CreateSelect(Ret0, Zero, Dividend);
>> + Value* EarlyRet = Builder.CreateOr(Ret0, RetDividend);
>> + Builder.CreateCondBr(EarlyRet, End, BB1);
>> +
>> + // ; bb1: ; preds = %special-cases
>> + // ; %sr_1 = add i32 %sr, 1
>> + // ; %tmp2 = sub i32 31, %sr
>> + // ; %q = shl i32 %dividend, %tmp2
>> + // ; %skipLoop = icmp eq i32 %sr_1, 0
>> + // ; br i1 %skipLoop, label %loop-exit, label %preheader
>> + Builder.SetInsertPoint(BB1);
>> + Value* SR_1 = Builder.CreateAdd(SR, One);
>> + Value* Tmp2 = Builder.CreateSub(ThirtyOne, SR);
>> + Value* Q = Builder.CreateShl(Dividend, Tmp2);
>> + Value* SkipLoop = Builder.CreateICmpEQ(SR_1, Zero);
>> + Builder.CreateCondBr(SkipLoop, LoopExit, Preheader);
>> +
>> + // ; preheader: ; preds = %bb1
>> + // ; %tmp3 = lshr i32 %dividend, %sr_1
>> + // ; %tmp4 = add i32 %divisor, -1
>> + // ; br label %do-while
>> + Builder.SetInsertPoint(Preheader);
>> + Value* Tmp3 = Builder.CreateLShr(Dividend, SR_1);
>> + Value* Tmp4 = Builder.CreateAdd(Divisor, NegOne);
>> + Builder.CreateBr(DoWhile);
>> +
>> + // ; do-while: ; preds = %do-while, %preheader
>> + // ; %carry_1 = phi i32 [ 0, %preheader ], [ %carry, %do-while ]
>> + // ; %sr_3 = phi i32 [ %sr_1, %preheader ], [ %sr_2, %do-while ]
>> + // ; %r_1 = phi i32 [ %tmp3, %preheader ], [ %r, %do-while ]
>> + // ; %q_2 = phi i32 [ %q, %preheader ], [ %q_1, %do-while ]
>> + // ; %tmp5 = shl i32 %r_1, 1
>> + // ; %tmp6 = lshr i32 %q_2, 31
>> + // ; %tmp7 = or i32 %tmp5, %tmp6
>> + // ; %tmp8 = shl i32 %q_2, 1
>> + // ; %q_1 = or i32 %carry_1, %tmp8
>> + // ; %tmp9 = sub i32 %tmp4, %tmp7
>> + // ; %tmp10 = ashr i32 %tmp9, 31
>> + // ; %carry = and i32 %tmp10, 1
>> + // ; %tmp11 = and i32 %tmp10, %divisor
>> + // ; %r = sub i32 %tmp7, %tmp11
>> + // ; %sr_2 = add i32 %sr_3, -1
>> + // ; %tmp12 = icmp eq i32 %sr_2, 0
>> + // ; br i1 %tmp12, label %loop-exit, label %do-while
>> + Builder.SetInsertPoint(DoWhile);
>> + PHINode* Carry_1 = Builder.CreatePHI(I32Ty, 2);
>> + PHINode* SR_3 = Builder.CreatePHI(I32Ty, 2);
>> + PHINode* R_1 = Builder.CreatePHI(I32Ty, 2);
>> + PHINode* Q_2 = Builder.CreatePHI(I32Ty, 2);
>> + Value* Tmp5 = Builder.CreateShl(R_1, One);
>> + Value* Tmp6 = Builder.CreateLShr(Q_2, ThirtyOne);
>> + Value* Tmp7 = Builder.CreateOr(Tmp5, Tmp6);
>> + Value* Tmp8 = Builder.CreateShl(Q_2, One);
>> + Value* Q_1 = Builder.CreateOr(Carry_1, Tmp8);
>> + Value* Tmp9 = Builder.CreateSub(Tmp4, Tmp7);
>> + Value* Tmp10 = Builder.CreateAShr(Tmp9, 31);
>> + Value* Carry = Builder.CreateAnd(Tmp10, One);
>> + Value* Tmp11 = Builder.CreateAnd(Tmp10, Divisor);
>> + Value* R = Builder.CreateSub(Tmp7, Tmp11);
>> + Value* SR_2 = Builder.CreateAdd(SR_3, NegOne);
>> + Value* Tmp12 = Builder.CreateICmpEQ(SR_2, Zero);
>> + Builder.CreateCondBr(Tmp12, LoopExit, DoWhile);
>> +
>> + // ; loop-exit: ; preds = %do-while, %bb1
>> + // ; %carry_2 = phi i32 [ 0, %bb1 ], [ %carry, %do-while ]
>> + // ; %q_3 = phi i32 [ %q, %bb1 ], [ %q_1, %do-while ]
>> + // ; %tmp13 = shl i32 %q_3, 1
>> + // ; %q_4 = or i32 %carry_2, %tmp13
>> + // ; br label %end
>> + Builder.SetInsertPoint(LoopExit);
>> + PHINode* Carry_2 = Builder.CreatePHI(I32Ty, 2);
>> + PHINode* Q_3 = Builder.CreatePHI(I32Ty, 2);
>> + Value* Tmp13 = Builder.CreateShl(Q_3, One);
>> + Value* Q_4 = Builder.CreateOr(Carry_2, Tmp13);
>> + Builder.CreateBr(End);
>> +
>> + // ; end: ; preds = %loop-exit, %special-cases
>> + // ; %q_5 = phi i32 [ %q_4, %loop-exit ], [ %retVal, %special-cases ]
>> + // ; ret i32 %q_5
>> + Builder.SetInsertPoint(End, End->begin());
>> + PHINode* Q_5 = Builder.CreatePHI(I32Ty, 2);
>> +
>> + // Populate the Phis, since all values have now been created. Our Phis were:
>> + // ; %carry_1 = phi i32 [ 0, %preheader ], [ %carry, %do-while ]
>> + Carry_1->addIncoming(Zero, Preheader);
>> + Carry_1->addIncoming(Carry, DoWhile);
>> + // ; %sr_3 = phi i32 [ %sr_1, %preheader ], [ %sr_2, %do-while ]
>> + SR_3->addIncoming(SR_1, Preheader);
>> + SR_3->addIncoming(SR_2, DoWhile);
>> + // ; %r_1 = phi i32 [ %tmp3, %preheader ], [ %r, %do-while ]
>> + R_1->addIncoming(Tmp3, Preheader);
>> + R_1->addIncoming(R, DoWhile);
>> + // ; %q_2 = phi i32 [ %q, %preheader ], [ %q_1, %do-while ]
>> + Q_2->addIncoming(Q, Preheader);
>> + Q_2->addIncoming(Q_1, DoWhile);
>> + // ; %carry_2 = phi i32 [ 0, %bb1 ], [ %carry, %do-while ]
>> + Carry_2->addIncoming(Zero, BB1);
>> + Carry_2->addIncoming(Carry, DoWhile);
>> + // ; %q_3 = phi i32 [ %q, %bb1 ], [ %q_1, %do-while ]
>> + Q_3->addIncoming(Q, BB1);
>> + Q_3->addIncoming(Q_1, DoWhile);
>> + // ; %q_5 = phi i32 [ %q_4, %loop-exit ], [ %retVal, %special-cases ]
>> + Q_5->addIncoming(Q_4, LoopExit);
>> + Q_5->addIncoming(RetVal, SpecialCases);
>> +
>> + return Q_5;
>> +}
>> +
>> +bool llvm::expandDivision(BinaryOperator* Div) {
>> + assert(Div->getOpcode() == Instruction::SDiv ||
>> + Div->getOpcode() == Instruction::UDiv
>> + && "Trying to expand division from a non-division function");
>> +
>> + IRBuilder<> Builder(Div);
>> +
>> + if (Div->getType()->isVectorTy()) {
>> + assert(0 && "Div over vectors not supported");
>> + return false;
>> + }
>> +
>> + // First prepare the sign if it's a signed division
>> + if (Div->getOpcode() == Instruction::SDiv) {
>> + // Lower the code to unsigned division, and reset Div to point to the udiv.
>> + Value* Quotient = GenerateSignedDivisionCode(Div->getOperand(0),
>> + Div->getOperand(1), Builder);
>> + Div->replaceAllUsesWith(Quotient);
>> + Div->dropAllReferences();
>> + Div->eraseFromParent();
>> +
>> + // If we didn't actually generate a udiv instruction, we're done
>> + BinaryOperator* BO = dyn_cast<BinaryOperator>(Builder.GetInsertPoint());
>> + if (!BO || BO->getOpcode() != Instruction::UDiv)
>> + return true;
>> +
>> + Div = BO;
>> + }
>> +
>> + // Insert the unsigned division code
>> + Value* Quotient = GenerateUnsignedDivisionCode(Div->getOperand(0),
>> + Div->getOperand(1),
>> + Builder);
>> + Div->replaceAllUsesWith(Quotient);
>> + Div->dropAllReferences();
>> + Div->eraseFromParent();
>> +
>> + return true;
>> +}
>>
>>
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