6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2024-08-12 00:29:20 +00:00
Code Issues Projects Releases Wiki Activity
1c1ab8f53d
llvm-6502/lib/Transforms/Utils/IntegerDivision.cpp

305 lines
13 KiB
C++
Raw Blame History

//===-- 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);
// ; %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);
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())
llvm_unreachable("Div over vectors not supported");
// 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;
}
Reference in New Issue View Git Blame Copy Permalink