cmd/compile: don't assume args are always zero-extended

On amd64, we always zero-extend when loading arguments from the stack.
On arm64, we extend based on the type. This causes problems with
zeroUpper*Bits, which reports the top bits are zero when they aren't.

Fix it to use the type to decide if the top bits are really zero.

For tests, only f32 currently fails on arm64. Added other tests
just for future-proofing.

Update #66066

Change-Id: I2f13fb47198e139ef13c9a34eb1edc932eea3ee3
Reviewed-on: https://go-review.googlesource.com/c/go/+/571135
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
Reviewed-by: Carlos Amedee <[email protected]>
Reviewed-by: David Chase <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: randall77

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

@@ -1295,7 +1295,9 @@ func zeroUpper32Bits(x *Value, depth int) bool {
 		OpARM64MADDW, OpARM64MSUBW, OpARM64RORW, OpARM64RORWconst:
 		return true
 	case OpArg: // note: but not ArgIntReg
-		return x.Type.Size() == 4
+		// amd64 always loads args from the stack unsigned.
+		// most other architectures load them sign/zero extended based on the type.
+		return x.Type.Size() == 4 && (x.Type.IsUnsigned() || x.Block.Func.Config.arch == "amd64")
 	case OpPhi, OpSelect0, OpSelect1:
 		// Phis can use each-other as an arguments, instead of tracking visited values,
 		// just limit recursion depth.
@@ -1319,7 +1321,7 @@ func zeroUpper48Bits(x *Value, depth int) bool {
 	case OpAMD64MOVWQZX, OpAMD64MOVWload, OpAMD64MOVWloadidx1, OpAMD64MOVWloadidx2:
 		return true
 	case OpArg: // note: but not ArgIntReg
-		return x.Type.Size() == 2
+		return x.Type.Size() == 2 && (x.Type.IsUnsigned() || x.Block.Func.Config.arch == "amd64")
 	case OpPhi, OpSelect0, OpSelect1:
 		// Phis can use each-other as an arguments, instead of tracking visited values,
 		// just limit recursion depth.
@@ -1343,7 +1345,7 @@ func zeroUpper56Bits(x *Value, depth int) bool {
 	case OpAMD64MOVBQZX, OpAMD64MOVBload, OpAMD64MOVBloadidx1:
 		return true
 	case OpArg: // note: but not ArgIntReg
-		return x.Type.Size() == 1
+		return x.Type.Size() == 1 && (x.Type.IsUnsigned() || x.Block.Func.Config.arch == "amd64")
 	case OpPhi, OpSelect0, OpSelect1:
 		// Phis can use each-other as an arguments, instead of tracking visited values,
 		// just limit recursion depth.

test/fixedbugs/issue66066b.go

@@ -0,0 +1,58 @@
+// run
+
+// Copyright 2024 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 main
+
+//go:noinline
+func f32(_, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, x int32) uint64 {
+	return uint64(uint32(x))
+}
+
+//go:noinline
+func f16(_, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, x int16) uint64 {
+	return uint64(uint16(x))
+}
+
+//go:noinline
+func f8(_, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, x int8) uint64 {
+	return uint64(uint8(x))
+}
+
+//go:noinline
+func g32(_, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, x uint32) int64 {
+	return int64(int32(x))
+}
+
+//go:noinline
+func g16(_, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, x uint16) int64 {
+	return int64(int16(x))
+}
+
+//go:noinline
+func g8(_, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, x uint8) int64 {
+	return int64(int8(x))
+}
+
+func main() {
+	if got := f32(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1); got != 0xffffffff {
+		println("bad f32", got)
+	}
+	if got := f16(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1); got != 0xffff {
+		println("bad f16", got)
+	}
+	if got := f8(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1); got != 0xff {
+		println("bad f8", got)
+	}
+	if got := g32(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xffffffff); got != -1 {
+		println("bad g32", got)
+	}
+	if got := g16(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xffff); got != -1 {
+		println("bad g16", got)
+	}
+	if got := g8(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff); got != -1 {
+		println("bad g8", got)
+	}
+}