[IR] Convert profile metadata in createCallMatchingInvoke()

[yrouban]

Summary

When an invoke instruction is converted to a call its profile metadata is dropped because it has incompatible format (see https://reviews.llvm.org/D81996).
This patch adds an attempt to convert profile data to format of the call instruction. This used to work well before the patch https://reviews.llvm.org/D80618.

[hans]

Seems reasonable, but I don't know that much about profile info.. is it actually useful to have "branch_weights" metadata on a call? Isn't it enough that there's profile info on the branch towards the BB that has the call instruction? Or is this data used for something more?

[yrouban]

In D82071#2100391, @hans wrote:

Seems reasonable, but I don't know that much about profile info.. is it actually useful to have "branch_weights" metadata on a call? Isn't it enough that there's profile info on the branch towards the BB that has the call instruction? Or is this data used for something more?

Branch_weights are useful for call instructions as said in the LLVM LangRef (https://llvm.org/docs/BranchWeightMetadata.html).
Let us wait for @xur to comment.

[hans]

Branch_weights are useful for call instructions as said in the LLVM LangRef (https://llvm.org/docs/BranchWeightMetadata.html).
Let us wait for @xur to comment.

That doc initially says branch weights are only used on terminators, although I see call instructions mentioned further down. It would be good to get it updated :-)

[reames]

LGTM

(Just for reference, the total bit tripped me up at first, but the reasoning is that we're converting to a call, not proving the call no throw. We could still throw out.)

We probably should extend the call metadata to the two argument form to explicitly model the difference between normal and throw out.

llvm/lib/Transforms/Utils/Local.cpp

CallInst *llvm::createCallMatchingInvoke(InvokeInst *II) {
   II->getOperandBundlesAsDefs(OpBundles);
   CallInst *NewCall = CallInst::Create(II->getFunctionType(),
                                        II->getCalledOperand(), Args, OpBundles);
   NewCall->setCallingConv(II->getCallingConv());
   NewCall->setAttributes(II->getAttributes());
   NewCall->setDebugLoc(II->getDebugLoc());
   NewCall->copyMetadata(*II);
 
-  // If the invoke had profile metadata, drop it.
-  if (NewCall->hasMetadata(LLVMContext::MD_prof))
-    NewCall->setMetadata(LLVMContext::MD_prof, nullptr);
+  // If the invoke had profile metadata, try converting them for CallInst.
+  uint64_t TotalWeight;
+  if (NewCall->extractProfTotalWeight(TotalWeight)) {
+    // Set the total weight if it fits into i32, otherwise reset.
+    MDBuilder MDB(NewCall->getContext());
+    auto NewWeights = uint32_t(TotalWeight) != TotalWeight
+                          ? nullptr
+                          : MDB.createBranchWeights({uint32_t(TotalWeight)});
+    NewCall->setMetadata(LLVMContext::MD_prof, NewWeights);
+  }
 
   return NewCall;
 }
 
 /// changeToCall - Convert the specified invoke into a normal call.
 void llvm::changeToCall(InvokeInst *II, DomTreeUpdater *DTU) {
   CallInst *NewCall = createCallMatchingInvoke(II);
   NewCall->takeName(II);

llvm/test/Transforms/SimplifyCFG/invoke_unwind.ll

 ; RUN: opt < %s -simplifycfg -S | FileCheck %s
 
 declare void @bar()
 
 ; This testcase checks to see if the simplifycfg pass is converting invoke
 ; instructions to call instructions if the handler just rethrows the exception.
 define i32 @test1() personality i32 (...)* @__gxx_personality_v0 {
 ; CHECK-LABEL: @test1(
-; CHECK-NEXT: call void @bar()
-; CHECK-NOT: !prof
+; CHECK-NEXT: call void @bar(), !prof ![[PROF:[0-9]+]]
 ; CHECK-NEXT: ret i32 0
         invoke void @bar( )
                         to label %1 unwind label %Rethrow, !prof !0
         ret i32 0
 Rethrow:
         %exn = landingpad {i8*, i32}
                  catch i8* null
         resume { i8*, i32 } %exn
 }
 
-!0 = !{!"branch_weights", i32 369, i32 0}
+!0 = !{!"branch_weights", i32 369, i32 2}
 
 define i32 @test2() personality i32 (...)* @__gxx_personality_v0 {
 ; CHECK-LABEL: @test2(
 ; CHECK-NEXT: call void @bar() [ "foo"(i32 100) ]
 ; CHECK-NEXT: ret i32 0
         invoke void @bar( ) [ "foo"(i32 100) ]
                         to label %1 unwind label %Rethrow
         ret i32 0

   
 lpad2:
   %1 = landingpad { i8*, i32 }
           cleanup
   br label %rethrow
 }
 
 declare i32 @__gxx_personality_v0(...)
+
+; CHECK: ![[PROF]] = !{!"branch_weights", i32 371}