cmd/compile: accounts rematerialize ops's output reginfo

This CL implements the check for rematerializeable value's output
regspec at its remateralization site. It has some potential problems,
please see the TODO in regalloc.go.

Fixes golang#70451.

Cherry-picked from the dev.simd branch. This CL is not
necessarily SIMD specific. Apply early to reduce risk.

Change-Id: Ib624b967031776851136554719e939e9bf116b7c
Reviewed-on: https://go-review.googlesource.com/c/go/+/695315
Reviewed-by: David Chase <[email protected]>
TryBot-Bypass: David Chase <[email protected]>
Reviewed-on: https://go-review.googlesource.com/c/go/+/708857
Reviewed-by: Junyang Shao <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: JunyangShao

src/cmd/compile/internal/ssa/func.go

@@ -102,6 +102,7 @@ func (c *Config) NewFunc(fe Frontend, cache *Cache) *Func {
 		NamedValues:          make(map[LocalSlot][]*Value),
 		CanonicalLocalSlots:  make(map[LocalSlot]*LocalSlot),
 		CanonicalLocalSplits: make(map[LocalSlotSplitKey]*LocalSlot),
+		OwnAux:               &AuxCall{},
 	}
 }
 

src/cmd/compile/internal/ssa/func_test.go

@@ -250,6 +250,11 @@ func Exit(arg string) ctrl {
 	return ctrl{BlockExit, arg, []string{}}
 }
 
+// Ret specifies a BlockRet.
+func Ret(arg string) ctrl {
+	return ctrl{BlockRet, arg, []string{}}
+}
+
 // Eq specifies a BlockAMD64EQ.
 func Eq(cond, sub, alt string) ctrl {
 	return ctrl{BlockAMD64EQ, cond, []string{sub, alt}}

src/cmd/compile/internal/ssa/regalloc.go

@@ -609,6 +609,29 @@ func (s *regAllocState) allocValToReg(v *Value, mask regMask, nospill bool, pos
 	} else if v.rematerializeable() {
 		// Rematerialize instead of loading from the spill location.
 		c = v.copyIntoWithXPos(s.curBlock, pos)
+		// We need to consider its output mask and potentially issue a Copy
+		// if there are register mask conflicts.
+		// This currently happens for the SIMD package only between GP and FP
+		// register. Because Intel's vector extension can put integer value into
+		// FP, which is seen as a vector. Example instruction: VPSLL[BWDQ]
+		// Because GP and FP masks do not overlap, mask & outputMask == 0
+		// detects this situation thoroughly.
+		sourceMask := s.regspec(c).outputs[0].regs
+		if mask&sourceMask == 0 && !onWasmStack {
+			s.setOrig(c, v)
+			s.assignReg(s.allocReg(sourceMask, v), v, c)
+			// v.Type for the new OpCopy is likely wrong and it might delay the problem
+			// until ssa to asm lowering, which might need the types to generate the right
+			// assembly for OpCopy. For Intel's GP to FP move, it happens to be that
+			// MOV instruction has such a variant so it happens to be right.
+			// But it's unclear for other architectures or situations, and the problem
+			// might be exposed when the assembler sees illegal instructions.
+			// Right now make we still pick v.Type, because at least its size should be correct
+			// for the rematerialization case the amd64 SIMD package exposed.
+			// TODO: We might need to figure out a way to find the correct type or make
+			// the asm lowering use reg info only for OpCopy.
+			c = s.curBlock.NewValue1(pos, OpCopy, v.Type, c)
+		}
 	} else {
 		// Load v from its spill location.
 		spill := s.makeSpill(v, s.curBlock)

src/cmd/compile/internal/ssa/regalloc_test.go

@@ -6,6 +6,7 @@ package ssa
 
 import (
 	"cmd/compile/internal/types"
+	"cmd/internal/obj/x86"
 	"fmt"
 	"testing"
 )
@@ -279,3 +280,27 @@ func numOps(b *Block, op Op) int {
 	}
 	return n
 }
+
+func TestRematerializeableRegCompatible(t *testing.T) {
+	c := testConfig(t)
+	f := c.Fun("entry",
+		Bloc("entry",
+			Valu("mem", OpInitMem, types.TypeMem, 0, nil),
+			Valu("x", OpAMD64MOVLconst, c.config.Types.Int32, 1, nil),
+			Valu("a", OpAMD64POR, c.config.Types.Float32, 0, nil, "x", "x"),
+			Valu("res", OpMakeResult, types.NewResults([]*types.Type{c.config.Types.Float32, types.TypeMem}), 0, nil, "a", "mem"),
+			Ret("res"),
+		),
+	)
+	regalloc(f.f)
+	checkFunc(f.f)
+	moveFound := false
+	for _, v := range f.f.Blocks[0].Values {
+		if v.Op == OpCopy && x86.REG_X0 <= v.Reg() && v.Reg() <= x86.REG_X31 {
+			moveFound = true
+		}
+	}
+	if !moveFound {
+		t.Errorf("Expects an Copy to be issued, but got: %+v", f.f)
+	}
+}