compiler: open code string slice expressions

    
    Currently a string slice expression is implemented with a runtime
    call __go_string_slice. Change it to open code it, which is more
    efficient, and allows the backend to further optimize it.
    
    Also omit the write barrier for length-only update (i.e.
    s = s[:n]).
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/182540


git-svn-id: https://gcc.gnu.org/svn/gcc/trunk@272549 138bc75d-0d04-0410-961f-82ee72b054a4

3 files changed, 6 insertions, 41 deletions

diff --git a/libgo/Makefile.am b/libgo/Makefile.am
index 6324170816a..4bfed3facf7 100644
--- a/libgo/Makefile.am
+++ b/libgo/Makefile.am
@@ -468,7 +468,6 @@ runtime_files = \
 	runtime/go-runtime-error.c \
 	runtime/go-setenv.c \
 	runtime/go-signal.c \
-	runtime/go-strslice.c \
 	runtime/go-unsafe-pointer.c \
 	runtime/go-unsetenv.c \
 	runtime/go-unwind.c \
diff --git a/libgo/Makefile.in b/libgo/Makefile.in
index 08a39266ccc..837e1e8a621 100644
--- a/libgo/Makefile.in
+++ b/libgo/Makefile.in
@@ -248,12 +248,12 @@ am__objects_3 = runtime/aeshash.lo runtime/go-assert.lo \
 	runtime/go-nanotime.lo runtime/go-now.lo runtime/go-nosys.lo \
 	runtime/go-reflect-call.lo runtime/go-runtime-error.lo \
 	runtime/go-setenv.lo runtime/go-signal.lo \
-	runtime/go-strslice.lo runtime/go-unsafe-pointer.lo \
-	runtime/go-unsetenv.lo runtime/go-unwind.lo \
-	runtime/go-varargs.lo runtime/env_posix.lo runtime/panic.lo \
-	runtime/print.lo runtime/proc.lo runtime/runtime_c.lo \
-	runtime/stack.lo runtime/yield.lo runtime/go-context.lo \
-	$(am__objects_1) $(am__objects_2)
+	runtime/go-unsafe-pointer.lo runtime/go-unsetenv.lo \
+	runtime/go-unwind.lo runtime/go-varargs.lo \
+	runtime/env_posix.lo runtime/panic.lo runtime/print.lo \
+	runtime/proc.lo runtime/runtime_c.lo runtime/stack.lo \
+	runtime/yield.lo runtime/go-context.lo $(am__objects_1) \
+	$(am__objects_2)
 am_libgo_llgo_la_OBJECTS = $(am__objects_3)
 libgo_llgo_la_OBJECTS = $(am_libgo_llgo_la_OBJECTS)
 AM_V_lt = $(am__v_lt_@AM_V@)
@@ -901,7 +901,6 @@ runtime_files = \
 	runtime/go-runtime-error.c \
 	runtime/go-setenv.c \
 	runtime/go-signal.c \
-	runtime/go-strslice.c \
 	runtime/go-unsafe-pointer.c \
 	runtime/go-unsetenv.c \
 	runtime/go-unwind.c \
@@ -1362,8 +1361,6 @@ runtime/go-setenv.lo: runtime/$(am__dirstamp) \
 	runtime/$(DEPDIR)/$(am__dirstamp)
 runtime/go-signal.lo: runtime/$(am__dirstamp) \
 	runtime/$(DEPDIR)/$(am__dirstamp)
-runtime/go-strslice.lo: runtime/$(am__dirstamp) \
-	runtime/$(DEPDIR)/$(am__dirstamp)
 runtime/go-unsafe-pointer.lo: runtime/$(am__dirstamp) \
 	runtime/$(DEPDIR)/$(am__dirstamp)
 runtime/go-unsetenv.lo: runtime/$(am__dirstamp) \
@@ -1448,7 +1445,6 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@runtime/$(DEPDIR)/go-runtime-error.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@runtime/$(DEPDIR)/go-setenv.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@runtime/$(DEPDIR)/go-signal.Plo@am__quote@
-@AMDEP_TRUE@@am__include@ @am__quote@runtime/$(DEPDIR)/go-strslice.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@runtime/$(DEPDIR)/go-unsafe-pointer.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@runtime/$(DEPDIR)/go-unsetenv.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@runtime/$(DEPDIR)/go-unwind.Plo@am__quote@
diff --git a/libgo/runtime/go-strslice.c b/libgo/runtime/go-strslice.c
deleted file mode 100644
index d51c2493781..00000000000
--- a/libgo/runtime/go-strslice.c
+++ /dev/null
@@ -1,30 +0,0 @@
-/* go-strslice.c -- the go string slice function.
-
-   Copyright 2009 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.  */
-
-#include "runtime.h"
-
-String
-__go_string_slice (String s, intgo start, intgo end)
-{
-  intgo len;
-  String ret;
-
-  len = s.len;
-  if (end == -1)
-    end = len;
-  if (start > len || end < start || end > len)
-    runtime_panicstring ("string index out of bounds");
-  ret.len = end - start;
-  // If the length of the new string is zero, the str field doesn't
-  // matter, so just set it to nil.  This avoids the problem of
-  // s.str + start pointing just past the end of the string,
-  // which may keep the next memory block alive unnecessarily.
-  if (ret.len == 0)
-    ret.str = nil;
-  else
-    ret.str = s.str + start;
-  return ret;
-}