From: Philip Reames <listmail@philipreames.com>
Date: Mon, 11 Feb 2019 23:34:33 +0000 (+0000)
Subject: Be conservative about unordered accesses for the moment
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=5021270f7bd6f63839c8ea18f6177a1c0a3170dd;p=llvm

Be conservative about unordered accesses for the moment

Background: As described in https://reviews.llvm.org/D57601, I'm working towards separating volatile and atomic in the MMO uses for atomic instructions.

In https://reviews.llvm.org/D57593, I fixed a bug where isUnordered was returning the wrong result, but didn't account for the fact I was getting slightly ahead of myself. While both uses of isUnordered are correct (as far as I can tell), we don't have tests to demonstrate this and being aggressive gets in the way of having the removal of volatile truly be non-functional. Once D57601 lands, I will return to these call sites, revert this patch, and add the appropriate tests to show the expected behaviour.

Differential Revision: https://reviews.llvm.org/D57802



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@353766 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/ImplicitNullChecks.cpp b/lib/CodeGen/ImplicitNullChecks.cpp
index 68110314151..75f4eef5dc1 100644
--- a/lib/CodeGen/ImplicitNullChecks.cpp
+++ b/lib/CodeGen/ImplicitNullChecks.cpp
@@ -235,8 +235,11 @@ bool ImplicitNullChecks::canHandle(const MachineInstr *MI) {
   assert(!llvm::any_of(MI->operands(), IsRegMask) &&
          "Calls were filtered out above!");
 
-  auto IsUnordered = [](MachineMemOperand *MMO) { return MMO->isUnordered(); };
-  return llvm::all_of(MI->memoperands(), IsUnordered);
+  // TODO: This should be isUnordered (see D57601) once test cases are written
+  // demonstrating that.
+  auto IsSimple = [](MachineMemOperand *MMO) {
+    return !MMO->isVolatile() && !MMO->isAtomic(); };
+  return llvm::all_of(MI->memoperands(), IsSimple);
 }
 
 ImplicitNullChecks::DependenceResult
diff --git a/lib/CodeGen/MachineInstr.cpp b/lib/CodeGen/MachineInstr.cpp
index 4c80b7bfb0b..0b8e9caa09b 100644
--- a/lib/CodeGen/MachineInstr.cpp
+++ b/lib/CodeGen/MachineInstr.cpp
@@ -1291,8 +1291,10 @@ bool MachineInstr::hasOrderedMemoryRef() const {
     return true;
 
   // Check if any of our memory operands are ordered.
+  // TODO: This should probably be be isUnordered (see D57601), but the callers
+  // need audited and test cases written to be sure.
   return llvm::any_of(memoperands(), [](const MachineMemOperand *MMO) {
-    return !MMO->isUnordered();
+    return MMO->isVolatile() || MMO->isAtomic();
   });
 }