[llvm] r353766 - Be conservative about unordered accesses for the moment

Philip Reames via llvm-commits llvm-commits at lists.llvm.org
Mon Feb 11 15:34:33 PST 2019

Author: reames
Date: Mon Feb 11 15:34:33 2019
New Revision: 353766

URL: http://llvm.org/viewvc/llvm-project?rev=353766&view=rev
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


Modified: llvm/trunk/lib/CodeGen/ImplicitNullChecks.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/ImplicitNullChecks.cpp?rev=353766&r1=353765&r2=353766&view=diff
--- llvm/trunk/lib/CodeGen/ImplicitNullChecks.cpp (original)
+++ llvm/trunk/lib/CodeGen/ImplicitNullChecks.cpp Mon Feb 11 15:34:33 2019
@@ -235,8 +235,11 @@ bool ImplicitNullChecks::canHandle(const
   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);

Modified: llvm/trunk/lib/CodeGen/MachineInstr.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineInstr.cpp?rev=353766&r1=353765&r2=353766&view=diff
--- llvm/trunk/lib/CodeGen/MachineInstr.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineInstr.cpp Mon Feb 11 15:34:33 2019
@@ -1291,8 +1291,10 @@ bool MachineInstr::hasOrderedMemoryRef()
     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();

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