Preserve important metadata in JumpThreadingPass::unfoldSelectInstr

[mmendell]

Summary

Useful metadata like llvm.loop can be lost when the new branch instruction is created. Grab that metadata from the old branch.
Add a LIT test to check

[mmendell]

ran git clang-format

[lattner]

I'm sorry but I haven't worked on this code in a very long time.

[mmendell]

@rp Could you please review this?

[nikic]

llvm/test/Transforms/JumpThreading/preserve-select-unfold.ll

4

Use update_test_checks.py with --check-globals, remove data layout and triple.

11

The metadata you are testing for appear to already be present without your patch: https://llvm.godbolt.org/z/GqW8oo5fb

[rp]

In D155214#4503253, @mmendell wrote:

@rp Could you please review this?

Thanks for the trust, but the change preserving metadata during jump-threading was my first LLVM commit, so my review would not be worth much.

[mmendell]

I see that this is not needed any more. No idea why my version of LLVM has this problem....

llvm/test/Transforms/JumpThreading/preserve-select-unfold.ll

4

Actually, this was the wrong test case :-). It was supposed to be https://llvm.godbolt.org/z/GKzGzEr7o. On the other hand, it seems to be working as well. I was basing my change on an older LLVM. I am trying to bring it up to trunk.

llvm/lib/Transforms/Scalar/JumpThreading.cpp

BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "select.unfold",
                                          BB->getParent(), BB);
   // Move the unconditional branch to NewBB.
   PredTerm->removeFromParent();
   PredTerm->insertInto(NewBB, NewBB->end());
   // Create a conditional branch and update PHI nodes.
   auto *BI = BranchInst::Create(NewBB, BB, SI->getCondition(), Pred);
   BI->applyMergedLocation(PredTerm->getDebugLoc(), SI->getDebugLoc());
   BI->copyMetadata(*SI, {LLVMContext::MD_prof});
+  // Also preserve the metadata from the branch
+  BI->copyMetadata(*PredTerm,
+                   {LLVMContext::MD_loop, LLVMContext::MD_annotation});
   SIUse->setIncomingValue(Idx, SI->getFalseValue());
   SIUse->addIncoming(SI->getTrueValue(), NewBB);
 
   uint64_t TrueWeight = 1;
   uint64_t FalseWeight = 1;
   // Copy probabilities from 'SI' to created conditional branch in 'Pred'.
   if (extractBranchWeights(*SI, TrueWeight, FalseWeight) &&
       (TrueWeight + FalseWeight) != 0) {

llvm/test/Transforms/JumpThreading/preserve-select-unfold.ll

+; RUN: opt -passes=jump-threading -S < %s | FileCheck %s
+; Ensure that we preserve llvm.loop information
+target datalayout = "e-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024"
+target triple = "spir64-unknown-unknown-intelfpga"
+
+define spir_kernel void @test(i1 %Input) {
+entry:
+  br label %A
+
+; CHECK-LAB: select.unfold:
+; CHECK: br label %A, !llvm.loop ![[INFO:.*]]
+
+; CHECK-LAB: A:
+A:
+  %current_state.0.i.i = phi i32 [ 0, %entry ], [ %X, %M ]
+  %B = icmp eq i32 %current_state.0.i.i, 0
+  br i1 %B, label %M, label %B2
+
+B2:
+  ret void
+
+M:
+  %X = select i1 %Input, i32 2, i32 0
+  br label %A, !llvm.loop !0
+}
+
+; CHECK: ![[INFO]] = distinct !{![[INFO]], ![[LINFO:.*]]}
+!0 = distinct !{!0, !1}
+; CHECK: ![[LINFO]] = !{!"llvm.loop.ii.count", i32 1}
+!1 = !{!"llvm.loop.ii.count", i32 1}