[llvm] [MachineLoopInfo] Fix getLoopID to handle multi latches. (PR #106195)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: Freddy Ye (FreddyLeaf)

<details>
<summary>Changes</summary>

This patch also fixed CodegenPrepare to reserve loop metadata when merging blocks.

This fixes issue #<!-- -->102632

---
Full diff: https://github.com/llvm/llvm-project/pull/106195.diff


3 Files Affected:

- (modified) llvm/lib/CodeGen/CodeGenPrepare.cpp (+6) 
- (modified) llvm/lib/CodeGen/MachineLoopInfo.cpp (-2) 
- (modified) llvm/test/CodeGen/X86/code-align-loops.ll (+1-1) 


``````````diff
diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index bf48c1fdab0ff0..c63a265fe27789 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -1183,6 +1183,12 @@ void CodeGenPrepare::eliminateMostlyEmptyBlock(BasicBlock *BB) {
     }
   }
 
+  // Reserve loop Metadata.
+  if (BI->hasMetadata(LLVMContext::MD_loop)) {
+    for (auto *Pred : predecessors(BB))
+      Pred->getTerminator()->copyMetadata(*BI, LLVMContext::MD_loop);
+  }
+
   // The PHIs are now updated, change everything that refers to BB to use
   // DestBB and remove BB.
   BB->replaceAllUsesWith(DestBB);
diff --git a/llvm/lib/CodeGen/MachineLoopInfo.cpp b/llvm/lib/CodeGen/MachineLoopInfo.cpp
index 88ba10fbe29a91..b82b41fac662d7 100644
--- a/llvm/lib/CodeGen/MachineLoopInfo.cpp
+++ b/llvm/lib/CodeGen/MachineLoopInfo.cpp
@@ -211,8 +211,6 @@ MDNode *MachineLoop::getLoopID() const {
             break;
           }
         }
-        if (!MD)
-          return nullptr;
         if (!LoopID)
           LoopID = MD;
         else if (MD != LoopID)
diff --git a/llvm/test/CodeGen/X86/code-align-loops.ll b/llvm/test/CodeGen/X86/code-align-loops.ll
index 616478993a51da..40ad3b4c8d600e 100644
--- a/llvm/test/CodeGen/X86/code-align-loops.ll
+++ b/llvm/test/CodeGen/X86/code-align-loops.ll
@@ -111,7 +111,7 @@ for.body5:                                        ; preds = %for.body, %for.body
 ;     }
 ; }
 ; CHECK-LABEL: test3_multilatch:
-; ALIGN: .p2align 4, 0x90
+; ALIGN: .p2align 6, 0x90
 ; ALIGN-NEXT: .LBB2_1: # %while.cond
 define dso_local i32 @test3_multilatch() #0 {
 entry:

``````````

</details>


https://github.com/llvm/llvm-project/pull/106195