diff mbox series

Go patch committed: load LHS subexpressions of op= only once

Message ID CAOyqgcXfayCh6QJkgVd2qpTCG6SwmqTQ0y5i+fkyK8KnpVK-Eg@mail.gmail.com
State Committed
Commit 1bfb823e2a7346ef55bd53a5354770599f7a550b
Headers
Series Go patch committed: load LHS subexpressions of op= only once |

Commit Message

Ian Lance Taylor May 17, 2022, 10:48 p.m. UTC 
  This patch to the Go frontend loads LHS subexpressions of op=
assignment only once.  This avoids inconsistencies if the variables
are changed by evaluating the RHS.  This fixes
https://go.dev/issue/52811.  Bootstrapped and ran Go testsuite on
x86_64-pc-linux-gnu.  Committed to mainline.  There is a test case in
the main Go repo that will be copied over at some point.

Ian
88c35c4d23e2458687508187601f8d2b8570bbe3
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Patch

diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index daa725f9de9..5fa8becde3e 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -1,4 +1,4 @@ 
-f5bc28a30b7503015bbef38afb5812313184e822
+9d07072e58ca4f9f05343dfd3475b9f49dae5ec5
 
 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/statements.cc b/gcc/go/gofrontend/statements.cc
index 95fa3c48709..b3db843365e 100644
--- a/gcc/go/gofrontend/statements.cc
+++ b/gcc/go/gofrontend/statements.cc
@@ -1260,6 +1260,16 @@  Assignment_operation_statement::do_lower(Gogo*, Named_object*,
   Move_ordered_evals moe(b);
   this->lhs_->traverse_subexpressions(&moe);
 
+  // We can still be left with subexpressions that have to be loaded
+  // even if they don't have side effects themselves, in case the RHS
+  // changes variables named on the LHS.
+  int i;
+  if (this->lhs_->must_eval_subexpressions_in_order(&i))
+    {
+      Move_subexpressions ms(i, b);
+      this->lhs_->traverse_subexpressions(&ms);
+    }
+
   Expression* lval = this->lhs_->copy();
 
   Operator op;