Go patch committed: correct file reading logic in Stream_from_file

[Ian Lance Taylor via Gcc-patches]

This Go frontend patch by Nikhil Benesch fixes the file reading logic
in the Stream_from_file class.  That class is almost never used, and I
guess nobody noticed these problems.  Bootstrapped and ran Go
testsuite on x86_64-pc-linux-gnu.  Committed to mainline.

Ian

500c2690e24054730a2ecf9989720e9d501c9eb1
diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index 94827406df1..701b2d427e3 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -1,4 +1,4 @@
-801c458a562d22260ff176c26d65639dd32c8a90
+d00febdab0535546ccbf1ef634be1f23b09c8b77
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
diff --git a/gcc/go/gofrontend/import.cc b/gcc/go/gofrontend/import.cc
index c63ae24f533..081afefa083 100644
--- a/gcc/go/gofrontend/import.cc
+++ b/gcc/go/gofrontend/import.cc
@@ -1487,7 +1487,7 @@ Stream_from_file::~Stream_from_file()
 bool
 Stream_from_file::do_peek(size_t length, const char** bytes)
 {
-  if (this->data_.length() <= length)
+  if (this->data_.length() >= length)
     {
       *bytes = this->data_.data();
       return true;
@@ -1504,7 +1504,7 @@ Stream_from_file::do_peek(size_t length, const char** 
bytes)
       return false;
     }
 
-  if (lseek(this->fd_, - got, SEEK_CUR) != 0)
+  if (lseek(this->fd_, - got, SEEK_CUR) < 0)
     {
       if (!this->saw_error())
        go_fatal_error(Linemap::unknown_location(), "lseek failed: %m");
@@ -1524,7 +1524,7 @@ Stream_from_file::do_peek(size_t length, const char** 
bytes)
 void
 Stream_from_file::do_advance(size_t skip)
 {
-  if (lseek(this->fd_, skip, SEEK_CUR) != 0)
+  if (lseek(this->fd_, skip, SEEK_CUR) < 0)
     {
       if (!this->saw_error())
        go_fatal_error(Linemap::unknown_location(), "lseek failed: %m");
@@ -1532,7 +1532,7 @@ Stream_from_file::do_advance(size_t skip)
     }
   if (!this->data_.empty())
     {
-      if (this->data_.length() < skip)
+      if (this->data_.length() > skip)
        this->data_.erase(0, skip);
       else
        this->data_.clear();