[llvm] Fix SCC enter block collection in BPI (PR #210580)

[via llvm-commits]

https://github.com/SomeFlyingThing updated https://github.com/llvm/llvm-project/pull/210580

>From cac5a3984be931effb38e1aaf8a69cce34b72c6f Mon Sep 17 00:00:00 2001
From: SomeFlyingThing <306498559+SomeFlyingThing at users.noreply.github.com>
Date: Sun, 19 Jul 2026 09:16:13 +0100
Subject: [PATCH] Fix SCC enter block collection in BPI

---
 llvm/lib/Analysis/BranchProbabilityInfo.cpp   |  2 +-
 .../Analysis/BranchProbabilityInfo/loop.ll    | 30 +++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Analysis/BranchProbabilityInfo.cpp b/llvm/lib/Analysis/BranchProbabilityInfo.cpp
index 1b0a8b8e74f4a..feb0b34cd4c48 100644
--- a/llvm/lib/Analysis/BranchProbabilityInfo.cpp
+++ b/llvm/lib/Analysis/BranchProbabilityInfo.cpp
@@ -391,7 +391,7 @@ void BPIConstruction::SccInfo::getSccEnterBlocks(
     if (isSCCHeader(BB, SccNum))
       for (const auto *Pred : predecessors(BB))
         if (getSCCNum(Pred) != SccNum)
-          Enters.push_back(const_cast<BasicBlock *>(BB));
+          Enters.push_back(const_cast<BasicBlock *>(Pred));
   }
 }
 
diff --git a/llvm/test/Analysis/BranchProbabilityInfo/loop.ll b/llvm/test/Analysis/BranchProbabilityInfo/loop.ll
index ffac1cd466641..e6b8429eddaa7 100644
--- a/llvm/test/Analysis/BranchProbabilityInfo/loop.ll
+++ b/llvm/test/Analysis/BranchProbabilityInfo/loop.ll
@@ -722,4 +722,34 @@ exit:
 }
 
 
+; Check that a cold irreducible loop propagates its estimated weight through
+; the blocks entering the SCC.
+define void @test19(i1 %arg, i1 %arg2, i1 %arg3, i1 %arg4) {
+; CHECK: edge %entry -> %dispatch probability is 0x078780e3 / 0x80000000 = 5.88%
+; CHECK: edge %entry -> %exit probability is 0x78787f1d / 0x80000000 = 94.12% [HOT edge]
+
+entry:
+  br i1 %arg, label %dispatch, label %exit
+
+dispatch:
+  br i1 %arg2, label %entry1, label %entry2
+
+entry1:
+  br label %loop1
+
+entry2:
+  br label %loop2
+
+loop1:
+  br i1 %arg3, label %loop2, label %cold
+
+loop2:
+  br i1 %arg4, label %loop1, label %cold
 
+cold:
+  call void @cold()
+  br label %exit
+
+exit:
+  ret void
+}