cmd/compile: don't assume pointer of a slice is non-nil

unsafe.SliceData can return pointers which are nil. That function gets
lowered to the SSA OpSlicePtr, which the compiler assumes is non-nil.
This used to be the case as OpSlicePtr was only used in situations
where the bounds check already passed. But with unsafe.SliceData that
is no longer the case.

There are situations where we know it is nil. Use Bounded() to
indicate that.

I looked through all the uses of OSPTR and added SetBounded where it
made sense. Most OSPTR results are passed directly to runtime calls
(e.g. memmove), so even if we know they are non-nil that info isn't
helpful.

Fixes #59293

Change-Id: I437a15330db48e0082acfb1f89caf8c56723fc51
Reviewed-on: https://go-review.googlesource.com/c/go/+/479896
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/cmd/compile/internal/ir/node.go b/src/cmd/compile/internal/ir/node.go
index ad25b9ff32..bdc40a8e7c 100644
--- a/src/cmd/compile/internal/ir/node.go
+++ b/src/cmd/compile/internal/ir/node.go
@@ -292,7 +292,7 @@ const (
 	OEFACE         // itable and data words of an empty-interface value.
 	OITAB          // itable word of an interface value.
 	OIDATA         // data word of an interface value in X
-	OSPTR          // base pointer of a slice or string.
+	OSPTR          // base pointer of a slice or string. Bounded==1 means known non-nil.
 	OCFUNC         // reference to c function pointer (not go func value)
 	OCHECKNIL      // emit code to ensure pointer/interface not nil
 	ORESULT        // result of a function call; Xoffset is stack offset