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📁 ..
📄 README.md(8.14 KB)
📄 TODO(950 B)
📄 addressingmodes.go(23.64 KB)
📄 bench_test.go(531 B)
📄 biasedsparsemap.go(2.71 KB)
📄 block.go(11.1 KB)
📄 branchelim.go(11.98 KB)
📄 branchelim_test.go(5.21 KB)
📄 cache.go(2.46 KB)
📄 check.go(16.59 KB)
📄 checkbce.go(956 B)
📄 compile.go(18.19 KB)
📄 config.go(11.7 KB)
📄 copyelim.go(1.83 KB)
📄 copyelim_test.go(1.29 KB)
📄 critical.go(3.19 KB)
📄 cse.go(9.43 KB)
📄 cse_test.go(4.25 KB)
📄 deadcode.go(9.61 KB)
📄 deadcode_test.go(3.49 KB)
📄 deadstore.go(9.08 KB)
📄 deadstore_test.go(4.09 KB)
📄 debug.go(56.34 KB)
📄 debug_lines_test.go(8.29 KB)
📄 debug_test.go(28.75 KB)
📄 decompose.go(13.41 KB)
📄 dom.go(7.98 KB)
📄 dom_test.go(13.34 KB)
📄 expand_calls.go(63.5 KB)
📄 export_test.go(3.23 KB)
📄 flagalloc.go(6.68 KB)
📄 flags_amd64_test.s(533 B)
📄 flags_arm64_test.s(699 B)
📄 flags_test.go(2.49 KB)
📄 func.go(27.08 KB)
📄 func_test.go(13.07 KB)
📄 fuse.go(6.5 KB)
📄 fuse_branchredirect.go(3.24 KB)
📄 fuse_comparisons.go(4.04 KB)
📄 fuse_test.go(7.21 KB)
📁 gen
📄 html.go(34.72 KB)
📄 id.go(576 B)
📄 layout.go(4.82 KB)
📄 lca.go(3.77 KB)
📄 lca_test.go(1.65 KB)
📄 likelyadjust.go(15.24 KB)
📄 location.go(3.06 KB)
📄 loopbce.go(10.54 KB)
📄 loopreschedchecks.go(15.86 KB)
📄 looprotate.go(2.61 KB)
📄 lower.go(1.36 KB)
📄 magic.go(15.77 KB)
📄 magic_test.go(9.1 KB)
📄 nilcheck.go(11.06 KB)
📄 nilcheck_test.go(12.17 KB)
📄 numberlines.go(7.83 KB)
📄 op.go(18.65 KB)
📄 opGen.go(1.01 MB)
📄 opt.go(308 B)
📄 passbm_test.go(3.14 KB)
📄 phielim.go(1.48 KB)
📄 phiopt.go(8.08 KB)
📄 poset.go(37.2 KB)
📄 poset_test.go(18.14 KB)
📄 print.go(3.85 KB)
📄 prove.go(41.82 KB)
📄 regalloc.go(83.69 KB)
📄 regalloc_test.go(6.49 KB)
📄 rewrite.go(53.49 KB)
📄 rewrite386.go(289.01 KB)
📄 rewrite386splitload.go(4.05 KB)
📄 rewriteAMD64.go(888.95 KB)
📄 rewriteAMD64splitload.go(21.41 KB)
📄 rewriteARM.go(487.7 KB)
📄 rewriteARM64.go(751.84 KB)
📄 rewriteCond_test.go(10.62 KB)
📄 rewriteLOONG64.go(193.44 KB)
📄 rewriteMIPS.go(174.44 KB)
📄 rewriteMIPS64.go(195.55 KB)
📄 rewritePPC64.go(431.6 KB)
📄 rewriteRISCV64.go(159.66 KB)
📄 rewriteS390X.go(433.4 KB)
📄 rewriteWasm.go(109.86 KB)
📄 rewrite_test.go(6.91 KB)
📄 rewritedec.go(10.16 KB)
📄 rewritedec64.go(63.77 KB)
📄 rewritegeneric.go(617.96 KB)
📄 schedule.go(18.23 KB)
📄 schedule_test.go(2.91 KB)
📄 shift_test.go(4.05 KB)
📄 shortcircuit.go(12.63 KB)
📄 shortcircuit_test.go(1.31 KB)
📄 sizeof_test.go(855 B)
📄 softfloat.go(1.99 KB)
📄 sparsemap.go(1.98 KB)
📄 sparseset.go(1.54 KB)
📄 sparsetree.go(8.05 KB)
📄 stackalloc.go(12.79 KB)
📄 stackframe.go(290 B)
📄 stmtlines_test.go(2.96 KB)
📁 testdata
📄 tighten.go(4.3 KB)
📄 trim.go(4.24 KB)
📄 tuple.go(1.97 KB)
📄 value.go(15.21 KB)
📄 writebarrier.go(19.29 KB)
📄 writebarrier_test.go(1.75 KB)
📄 xposmap.go(3.29 KB)
📄 zcse.go(2.07 KB)
📄 zeroextension_test.go(1.66 KB)

Editing: tighten.go

// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package ssa

// tighten moves Values closer to the Blocks in which they are used.
// This can reduce the amount of register spilling required,
// if it doesn't also create more live values.
// A Value can be moved to any block that
// dominates all blocks in which it is used.
func tighten(f *Func) {
	canMove := make([]bool, f.NumValues())
	for _, b := range f.Blocks {
		for _, v := range b.Values {
			if v.Op.isLoweredGetClosurePtr() {
				// Must stay in the entry block.
				continue
			}
			switch v.Op {
			case OpPhi, OpArg, OpArgIntReg, OpArgFloatReg, OpSelect0, OpSelect1, OpSelectN:
				// Phis need to stay in their block.
				// Arg must stay in the entry block.
				// Tuple selectors must stay with the tuple generator.
				// SelectN is typically, ultimately, a register.
				continue
			}
			if v.MemoryArg() != nil {
				// We can't move values which have a memory arg - it might
				// make two memory values live across a block boundary.
				continue
			}
			// Count arguments which will need a register.
			narg := 0
			for _, a := range v.Args {
				if !a.rematerializeable() {
					narg++
				}
			}
			if narg >= 2 && !v.Type.IsFlags() {
				// Don't move values with more than one input, as that may
				// increase register pressure.
				// We make an exception for flags, as we want flag generators
				// moved next to uses (because we only have 1 flag register).
				continue
			}
			canMove[v.ID] = true
		}
	}

// Build data structure for fast least-common-ancestor queries.
	lca := makeLCArange(f)

// For each moveable value, record the block that dominates all uses found so far.
	target := make([]*Block, f.NumValues())

// Grab loop information.
	// We use this to make sure we don't tighten a value into a (deeper) loop.
	idom := f.Idom()
	loops := f.loopnest()
	loops.calculateDepths()

changed := true
	for changed {
		changed = false

// Reset target
		for i := range target {
			target[i] = nil
		}

// Compute target locations (for moveable values only).
		// target location = the least common ancestor of all uses in the dominator tree.
		for _, b := range f.Blocks {
			for _, v := range b.Values {
				for i, a := range v.Args {
					if !canMove[a.ID] {
						continue
					}
					use := b
					if v.Op == OpPhi {
						use = b.Preds[i].b
					}
					if target[a.ID] == nil {
						target[a.ID] = use
					} else {
						target[a.ID] = lca.find(target[a.ID], use)
					}
				}
			}
			for _, c := range b.ControlValues() {
				if !canMove[c.ID] {
					continue
				}
				if target[c.ID] == nil {
					target[c.ID] = b
				} else {
					target[c.ID] = lca.find(target[c.ID], b)
				}
			}
		}

// If the target location is inside a loop,
		// move the target location up to just before the loop head.
		for _, b := range f.Blocks {
			origloop := loops.b2l[b.ID]
			for _, v := range b.Values {
				t := target[v.ID]
				if t == nil {
					continue
				}
				targetloop := loops.b2l[t.ID]
				for targetloop != nil && (origloop == nil || targetloop.depth > origloop.depth) {
					t = idom[targetloop.header.ID]
					target[v.ID] = t
					targetloop = loops.b2l[t.ID]
				}
			}
		}

// Move values to target locations.
		for _, b := range f.Blocks {
			for i := 0; i < len(b.Values); i++ {
				v := b.Values[i]
				t := target[v.ID]
				if t == nil || t == b {
					// v is not moveable, or is already in correct place.
					continue
				}
				// Move v to the block which dominates its uses.
				t.Values = append(t.Values, v)
				v.Block = t
				last := len(b.Values) - 1
				b.Values[i] = b.Values[last]
				b.Values[last] = nil
				b.Values = b.Values[:last]
				changed = true
				i--
			}
		}
	}
}

// phiTighten moves constants closer to phi users.
// This pass avoids having lots of constants live for lots of the program.
// See issue 16407.
func phiTighten(f *Func) {
	for _, b := range f.Blocks {
		for _, v := range b.Values {
			if v.Op != OpPhi {
				continue
			}
			for i, a := range v.Args {
				if !a.rematerializeable() {
					continue // not a constant we can move around
				}
				if a.Block == b.Preds[i].b {
					continue // already in the right place
				}
				// Make a copy of a, put in predecessor block.
				v.SetArg(i, a.copyInto(b.Preds[i].b))
			}
		}
	}
}

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Editing: tighten.go

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