Adding upstream version 1.18.10.upstream/1.18.10upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 165 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/ssa/tighten.go b/src/cmd/compile/internal/ssa/tighten.go
new file mode 100644
index 0000000..214bf62
--- /dev/null
+++ b/src/cmd/compile/internal/ssa/tighten.go
@@ -0,0 +1,165 @@
+// 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))
+			}
+		}
+	}
+}