cmd/compile: do not allow regalloc to LoadReg G register
On architectures where G is stored in a register, it is
possible for a variable to allocated to it, and subsequently
that variable may be spilled and reloaded, for example
because of an intervening call. If such an allocation
reaches a join point and it is the primary predecessor,
it becomes the target of a reload, which is only usually
right.
Fix: guard all the LoadReg ops, and spill value in the G
register (if any) before merges (in the same way that 387
FP registers are freed between blocks).
Includes test.
Fixes #25504.
Change-Id: I0482a53e20970c7315bf09c0e407ae5bba2fe05d
Reviewed-on: https://go-review.googlesource.com/114695
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
diff --git a/src/cmd/compile/internal/ssa/export_test.go b/src/cmd/compile/internal/ssa/export_test.go
index be9f19b..5832050 100644
--- a/src/cmd/compile/internal/ssa/export_test.go
+++ b/src/cmd/compile/internal/ssa/export_test.go
@@ -28,6 +28,7 @@
func testConfig(tb testing.TB) *Conf { return testConfigArch(tb, "amd64") }
func testConfigS390X(tb testing.TB) *Conf { return testConfigArch(tb, "s390x") }
+func testConfigARM64(tb testing.TB) *Conf { return testConfigArch(tb, "arm64") }
func testConfigArch(tb testing.TB, arch string) *Conf {
ctxt, ok := testCtxts[arch]
diff --git a/src/cmd/compile/internal/ssa/regalloc.go b/src/cmd/compile/internal/ssa/regalloc.go
index 080ad0f..bbf1932 100644
--- a/src/cmd/compile/internal/ssa/regalloc.go
+++ b/src/cmd/compile/internal/ssa/regalloc.go
@@ -532,6 +532,9 @@
}
s.assignReg(r, v, c)
+ if c.Op == OpLoadReg && s.isGReg(r) {
+ s.f.Fatalf("allocValToReg.OpLoadReg targeting g: " + c.LongString())
+ }
if nospill {
s.nospill |= regMask(1) << r
}
@@ -809,6 +812,10 @@
return opcodeTable[op].reg
}
+func (s *regAllocState) isGReg(r register) bool {
+ return s.f.Config.hasGReg && s.GReg == r
+}
+
func (s *regAllocState) regalloc(f *Func) {
regValLiveSet := f.newSparseSet(f.NumValues()) // set of values that may be live in register
defer f.retSparseSet(regValLiveSet)
@@ -951,6 +958,7 @@
// Majority vote? Deepest nesting level?
phiRegs = phiRegs[:0]
var phiUsed regMask
+
for _, v := range phis {
if !s.values[v.ID].needReg {
phiRegs = append(phiRegs, noRegister)
@@ -1516,6 +1524,9 @@
// predecessor of it, find live values that we use soon after
// the merge point and promote them to registers now.
if len(b.Succs) == 1 {
+ if s.f.Config.hasGReg && s.regs[s.GReg].v != nil {
+ s.freeReg(s.GReg) // Spill value in G register before any merge.
+ }
// For this to be worthwhile, the loop must have no calls in it.
top := b.Succs[0].b
loop := s.loopnest.b2l[top.ID]
@@ -1996,6 +2007,9 @@
c = e.p.NewValue1(pos, OpLoadReg, c.Type, c)
}
e.set(r, vid, c, false, pos)
+ if c.Op == OpLoadReg && e.s.isGReg(register(r.(*Register).num)) {
+ e.s.f.Fatalf("process.OpLoadReg targeting g: " + c.LongString())
+ }
}
}
@@ -2110,6 +2124,9 @@
}
}
e.set(loc, vid, x, true, pos)
+ if x.Op == OpLoadReg && e.s.isGReg(register(loc.(*Register).num)) {
+ e.s.f.Fatalf("processDest.OpLoadReg targeting g: " + x.LongString())
+ }
if splice != nil {
(*splice).Uses--
*splice = x
diff --git a/src/cmd/compile/internal/ssa/regalloc_test.go b/src/cmd/compile/internal/ssa/regalloc_test.go
index 02751a9..bb8be5e 100644
--- a/src/cmd/compile/internal/ssa/regalloc_test.go
+++ b/src/cmd/compile/internal/ssa/regalloc_test.go
@@ -36,6 +36,55 @@
checkFunc(f.f)
}
+// Test to make sure G register is never reloaded from spill (spill of G is okay)
+// See #25504
+func TestNoGetgLoadReg(t *testing.T) {
+ /*
+ Original:
+ func fff3(i int) *g {
+ gee := getg()
+ if i == 0 {
+ fff()
+ }
+ return gee // here
+ }
+ */
+ c := testConfigARM64(t)
+ f := c.Fun("b1",
+ Bloc("b1",
+ Valu("v1", OpInitMem, types.TypeMem, 0, nil),
+ Valu("v6", OpArg, c.config.Types.Int64, 0, c.Frontend().Auto(src.NoXPos, c.config.Types.Int64)),
+ Valu("v8", OpGetG, c.config.Types.Int64.PtrTo(), 0, nil, "v1"),
+ Valu("v11", OpARM64CMPconst, types.TypeFlags, 0, nil, "v6"),
+ Eq("v11", "b2", "b4"),
+ ),
+ Bloc("b4",
+ Goto("b3"),
+ ),
+ Bloc("b3",
+ Valu("v14", OpPhi, types.TypeMem, 0, nil, "v1", "v12"),
+ Valu("sb", OpSB, c.config.Types.Uintptr, 0, nil),
+ Valu("v16", OpARM64MOVDstore, types.TypeMem, 0, nil, "v8", "sb", "v14"),
+ Exit("v16"),
+ ),
+ Bloc("b2",
+ Valu("v12", OpARM64CALLstatic, types.TypeMem, 0, nil, "v1"),
+ Goto("b3"),
+ ),
+ )
+ regalloc(f.f)
+ checkFunc(f.f)
+ // Double-check that we never restore to the G register. Regalloc should catch it, but check again anyway.
+ r := f.f.RegAlloc
+ for _, b := range f.blocks {
+ for _, v := range b.Values {
+ if v.Op == OpLoadReg && r[v.ID].String() == "g" {
+ t.Errorf("Saw OpLoadReg targeting g register: %s", v.LongString())
+ }
+ }
+ }
+}
+
// Test to make sure we don't push spills into loops.
// See issue #19595.
func TestSpillWithLoop(t *testing.T) {
