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cmd/compile: do not allow regalloc to LoadReg G register

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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>
This commit is contained in:
David Chase 2018-05-25 16:08:13 -04:00
parent d5bc3b96c6
commit 31e1c30f55
3 changed files with 67 additions and 0 deletions
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1
src/cmd/compile/internal/ssa/export_test.go
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@ -28,6 +28,7 @@ var testCtxts = map[string]*obj.Link{
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]