[ConstantFoldTerminator] Preserve make.implicit metadata when converting SwitchInst to BranchInst

[• chenli]

Summary

llvm::ConstantFoldTerminator function can convert SwitchInst with single case (and default) to a conditional BranchInst. This patch adds support to preserve make.implicit metadata on this conversion.

[weimingz]

lib/Transforms/Utils/Local.cpp

232

LGTM.
just nitpick: the comment needs period.

[• chenli]

Add full stop to the end of the comment.

lib/Transforms/Utils/Local.cpp

if (SI->getNumCases() == 1) {
         assert(SICase && SIDef);
         // The TrueWeight should be the weight for the single case of SI.
         NewBr->setMetadata(LLVMContext::MD_prof,
                         MDBuilder(BB->getContext()).
                         createBranchWeights(SICase->getValue().getZExtValue(),
                                             SIDef->getValue().getZExtValue()));
       }
 
+      // Update make.implicit metadata to the newly-created conditional branch.
+      MDNode *MakeImplicitMD = SI->getMetadata(LLVMContext::MD_make_implicit);
+      if (MakeImplicitMD)
+        NewBr->setMetadata(LLVMContext::MD_make_implicit, MakeImplicitMD);
+
       // Delete the old switch.
       SI->eraseFromParent();
       return true;
     }
     return false;
   }
 
   if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {

test/Transforms/SimplifyCFG/preserve-make-implicit-on-switch-to-br.ll

+; RUN: opt %s -simplifycfg -S | FileCheck %s
+
+; ConstantFoldTerminator function can convert SwitchInst with one case (and default) to
+; a conditional BranchInst. This test checks the converted BranchInst preserve the 
+; make.implicit metadata.
+
+declare i32 @consume(i32*)
+declare void @trap()
+
+define i32 @copy-metadata(i32* %x) {
+
+entry:
+  %x.int = ptrtoint i32* %x to i64
+  
+; CHECK: br i1 %cond, label %is_null, label %default, !make.implicit !0
+  switch i64 %x.int, label %default [
+    i64 0, label %is_null
+  ], !make.implicit !0
+  
+default:
+  %0 = call i32 @consume(i32* %x)
+  ret i32 %0
+
+is_null:
+  call void @trap()
+  unreachable
+}
+
+!0 = !{}
+