[LTT] Mark as unkown weak function tests.

[mtrofin]

We don't have enough information to infer the probability of a weak function pointer being nullptr or not (open question if we could propagate this from the linker)

Issue #147390

[mtrofin]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• [LTT] Mark as unkown weak function tests. #167399 👈 (View in Graphite)
• [LTT][profcheck] Set branch weights for complex llvm.type.test lowering #167380
• [LP] Assign weights when peeling last iteration. #166858
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[mtrofin]

@pcc a question - would it be technically possible to propagate information about the weak function from [thin]link over to this point, and thus know if we even need a select in the first place?

[teresajohnson]

I would just add a TODO to consider that.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Mircea Trofin (mtrofin)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/167399.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/IPO/LowerTypeTests.cpp (+3)
• (modified) llvm/test/Transforms/LowerTypeTests/function-weak.ll (+3-2)

diff --git a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
index 961a2ba2f58e5..6c5045f7c84ff 100644
--- a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
+++ b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
@@ -1494,6 +1494,9 @@ void LowerTypeTestsModule::replaceWeakDeclarationWithJumpTablePtr(
                                      Constant::getNullValue(F->getType()));
     Value *Select = Builder.CreateSelect(ICmp, JT,
                                          Constant::getNullValue(F->getType()));
+    
+    if (auto *SI = dyn_cast<SelectInst>(Select))
+      setExplicitlyUnknownBranchWeightsIfProfiled(*SI, DEBUG_TYPE);
     // For phi nodes, we need to update the incoming value for all operands
     // with the same predecessor.
     if (PN)
diff --git a/llvm/test/Transforms/LowerTypeTests/function-weak.ll b/llvm/test/Transforms/LowerTypeTests/function-weak.ll
index 4ea03b6c2c1fa..dbbe8fa4a0a9a 100644
--- a/llvm/test/Transforms/LowerTypeTests/function-weak.ll
+++ b/llvm/test/Transforms/LowerTypeTests/function-weak.ll
@@ -32,10 +32,10 @@ target triple = "x86_64-unknown-linux-gnu"
 declare !type !0 extern_weak void @f()
 
 ; CHECK: define zeroext i1 @check_f()
-define zeroext i1 @check_f() {
+define zeroext i1 @check_f() !prof !{!"function_entry_count", i32 10} {
 entry:
 ; CHECK: [[CMP:%.*]] = icmp ne ptr @f, null
-; CHECK: [[SEL:%.*]] = select i1 [[CMP]], ptr @[[JT:.*]], ptr null
+; CHECK: [[SEL:%.*]] = select i1 [[CMP]], ptr @[[JT:.*]], ptr null, !prof ![[SELPROF:[0-9]+]]
 ; CHECK: [[PTI:%.*]] = ptrtoint ptr [[SEL]] to i1
 ; CHECK: ret i1 [[PTI]]
   ret i1 ptrtoint (ptr @f to i1)
@@ -165,3 +165,4 @@ define i1 @foo(ptr %p) {
 ; CHECK-NEXT: }
 
 !0 = !{i32 0, !"typeid1"}
+; CHECK: ![[SELPROF]] = !{!"unknown", !"lowertypetests"}
\ No newline at end of file

[teresajohnson]

lgtm

[teresajohnson]

I would just add a TODO to consider that.