[OpenMP] Fix non-determinism in clang copyin codegen

[ggeorgakoudis]

Summary

Codegen for OpeMP copyin has non-deterministic IR output due to the unspecified evaluation order in a codegen conditional branch, which makes automatic test generation unreliable. This patch refactors codegen code to avoid this non-determinism.

[ggeorgakoudis]

Update by Johanne's correction on the source of non-determinism

[jdoerfert]

LGTM, two nits, one below.

Add a sentence to the commit message describing the problem.

clang/lib/CodeGen/CGStmtOpenMP.cpp

1013

Rename A to MasterAddrInt and B to PrivateAddrInt, or similar.

[ggeorgakoudis]

Update for comments

[DavidSpickett]

Thanks! I'll test our Arm build and revert the requires once I've confirmed it passes.

[jdoerfert]

In D101952#2742237, @DavidSpickett wrote:

Thanks! I'll test our Arm build and revert the requires once I've confirmed it passes.

This is not the fix you need.

clang/lib/CodeGen/CGStmtOpenMP.cpp

for (const Expr *AssignOp : C->assignment_ops()) {
         }
         // Get the address of the threadprivate variable.
         Address PrivateAddr = EmitLValue(*IRef).getAddress(*this);
         if (CopiedVars.size() == 1) {
           // At first check if current thread is a master thread. If it is, no
           // need to copy data.
           CopyBegin = createBasicBlock("copyin.not.master");
           CopyEnd = createBasicBlock("copyin.not.master.end");
-          Builder.CreateCondBr(
-              Builder.CreateICmpNE(
-                  Builder.CreatePtrToInt(MasterAddr.getPointer(), CGM.IntPtrTy),
-                  Builder.CreatePtrToInt(PrivateAddr.getPointer(),
-                                         CGM.IntPtrTy)),
-              CopyBegin, CopyEnd);
+          auto *A =
+              Builder.CreatePtrToInt(MasterAddr.getPointer(), CGM.IntPtrTy);
+          auto *B =
+              Builder.CreatePtrToInt(PrivateAddr.getPointer(), CGM.IntPtrTy);
+          Builder.CreateCondBr(Builder.CreateICmpNE(A, B), CopyBegin, CopyEnd);
           EmitBlock(CopyBegin);
         }
         const auto *SrcVD =
             cast<VarDecl>(cast<DeclRefExpr>(*ISrcRef)->getDecl());
         const auto *DestVD =
             cast<VarDecl>(cast<DeclRefExpr>(*IDestRef)->getDecl());
         EmitOMPCopy(Type, PrivateAddr, MasterAddr, DestVD, SrcVD, AssignOp);
       }