74 lines
2.0 KiB
C++
74 lines
2.0 KiB
C++
//===-------------- lib/Support/BranchProbability.cpp -----------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements Branch Probability class.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Support/BranchProbability.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/Format.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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raw_ostream &BranchProbability::print(raw_ostream &OS) const {
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return OS << N << " / " << D << " = "
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<< format("%g%%", ((double)N / D) * 100.0);
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}
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void BranchProbability::dump() const { print(dbgs()) << '\n'; }
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static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) {
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assert(D && "divide by 0");
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// Fast path for multiplying by 1.0.
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if (!Num || D == N)
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return Num;
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// Split Num into upper and lower parts to multiply, then recombine.
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uint64_t ProductHigh = (Num >> 32) * N;
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uint64_t ProductLow = (Num & UINT32_MAX) * N;
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// Split into 32-bit digits.
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uint32_t Upper32 = ProductHigh >> 32;
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uint32_t Lower32 = ProductLow & UINT32_MAX;
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uint32_t Mid32Partial = ProductHigh & UINT32_MAX;
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uint32_t Mid32 = Mid32Partial + (ProductLow >> 32);
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// Carry.
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Upper32 += Mid32 < Mid32Partial;
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// Check for overflow.
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if (Upper32 >= D)
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return UINT64_MAX;
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uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
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uint64_t UpperQ = Rem / D;
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// Check for overflow.
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if (UpperQ > UINT32_MAX)
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return UINT64_MAX;
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Rem = ((Rem % D) << 32) | Lower32;
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uint64_t LowerQ = Rem / D;
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uint64_t Q = (UpperQ << 32) + LowerQ;
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// Check for overflow.
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return Q < LowerQ ? UINT64_MAX : Q;
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}
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uint64_t BranchProbability::scale(uint64_t Num) const {
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return ::scale(Num, N, D);
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}
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uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
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return ::scale(Num, D, N);
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}
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