cmd/compile: rewriteFixedLoad: ensure AuxInt is sign-extended

CL 701297 accidentailly broke the type casting behavior for Hash.

Previously, the generated rules for Hash shared a common pattern:

    v.AuxInt = int32ToAuxInt(fixed32(config, sym, off))

which inherently equaled to a signed-extend:

    v.AuxInt = int64(int32(types.TypeHash(...)))

The pattern in CL 701297 was however:

    v.AuxInt = int64(types.TypeHash(t))

Since types.TypeHash() returns a uint32, casting it to a wider integer
implies zero-extend. This diverges from the definition of AuxInt, in
which "Unused portions are filled by sign-extending the used portion,
even if the represented value is unsigned."

As a result, ssa.checkFunc(), where AuxInt is checked against the
mentioned rule, is unhappy and shouts:

    internal compiler error: 'typeAsserts': bad int32 AuxInt value for v1317

Reproduce it with:

    GOARCH=mips go tool compile -m -d=ssa/check/on test/devirtualization.go

This is only reproducible with GOARCH=mips/mipsle (cross and native).
Probably the rewrite rules of other architectures prevent Hash from
running into rewriteFixedLoad.

Fix it by emit sign-extend properly. Additionally, do the same for Kind_
as reflectdata.ABIKindOfType() also returns a fragile unsigned interger
(uint8).

Updates #67304

Change-Id: Ib4f3c94c0e3908698868449db2fdcdf4541f2e7e
Reviewed-on: https://go-review.googlesource.com/c/go/+/744860
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Jake Bailey <jacob.b.bailey@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/cmd/compile/internal/ssa/rewrite.go b/src/cmd/compile/internal/ssa/rewrite.go
index b093081884..21c905b04f 100644
--- a/src/cmd/compile/internal/ssa/rewrite.go
+++ b/src/cmd/compile/internal/ssa/rewrite.go
@@ -2171,11 +2171,11 @@ func rewriteFixedLoad(v *Value, sym Sym, sb *Value, off int64) *Value {
 					return v
 				case "Hash":
 					v.reset(OpConst32)
-					v.AuxInt = int64(types.TypeHash(t))
+					v.AuxInt = int64(int32(types.TypeHash(t)))
 					return v
 				case "Kind_":
 					v.reset(OpConst8)
-					v.AuxInt = int64(reflectdata.ABIKindOfType(t))
+					v.AuxInt = int64(int8(reflectdata.ABIKindOfType(t)))
 					return v
 				case "GCData":
 					gcdata, _ := reflectdata.GCSym(t, true)