Fix the source drift test.

Author: rlavaee

llvm/lib/CodeGen/BasicBlockSections.cpp

@@ -183,8 +183,7 @@ updateBranches(MachineFunction &MF,
 // clusters are ordered in increasing order of their IDs, with the "Exception"
 // and "Cold" succeeding all other clusters.
 // FuncClusterInfo represents the cluster information for basic blocks. It
-// maps from BBID of basic blocks to their cluster information. If this is
-// empty, it means unique sections for all basic blocks in the function.
+// maps from BBID of basic blocks to their cluster information.
 static void
 assignSections(MachineFunction &MF,
                const DenseMap<UniqueBBID, BBClusterInfo> &FuncClusterInfo) {
@@ -197,10 +196,8 @@ assignSections(MachineFunction &MF,
   for (auto &MBB : MF) {
     // With the 'all' option, every basic block is placed in a unique section.
     // With the 'list' option, every basic block is placed in a section
-    // associated with its cluster, unless we want individual unique sections
-    // for every basic block in this function (if FuncClusterInfo is empty).
-    if (MF.getTarget().getBBSectionsType() == llvm::BasicBlockSection::All ||
-        FuncClusterInfo.empty()) {
+    // associated with its cluster.
+    if (MF.getTarget().getBBSectionsType() == llvm::BasicBlockSection::All) {
       // If unique sections are desired for all basic blocks of the function, we
       // set every basic block's section ID equal to its original position in
       // the layout (which is equal to its number). This ensures that basic
@@ -308,19 +305,21 @@ bool BasicBlockSections::handleBBSections(MachineFunction &MF) {
   if (BBSectionsType == BasicBlockSection::List &&
       hasInstrProfHashMismatch(MF))
     return false;
-  // Renumber blocks before sorting them. This is useful for accessing the
-  // original layout positions and finding the original fallthroughs.
-  MF.RenumberBlocks();
 
   DenseMap<UniqueBBID, BBClusterInfo> FuncClusterInfo;
   if (BBSectionsType == BasicBlockSection::List) {
     auto ClusterInfo = getAnalysis<BasicBlockSectionsProfileReaderWrapperPass>()
                            .getClusterInfoForFunction(MF.getName());
+    if (ClusterInfo.empty()) return false;
     for (auto &BBClusterInfo : ClusterInfo) {
       FuncClusterInfo.try_emplace(BBClusterInfo.BBID, BBClusterInfo);
     }
   }
 
+  // Renumber blocks before sorting them. This is useful for accessing the
+  // original layout positions and finding the original fallthroughs.
+  MF.RenumberBlocks();
+
   MF.setBBSectionsType(BBSectionsType);
   assignSections(MF, FuncClusterInfo);
 

llvm/test/CodeGen/X86/basic-block-sections-source-drift.ll

@@ -1,6 +1,8 @@
-; RUN: echo "!foo" > %t.order.txt
-; RUN: llc < %s -mtriple=x86_64-pc-linux -basic-block-sections=%t.order.txt  | FileCheck --check-prefix=SOURCE-DRIFT %s
-; RUN: llc < %s -mtriple=x86_64-pc-linux -basic-block-sections=%t.order.txt -bbsections-detect-source-drift=false | FileCheck --check-prefix=HASH-CHECK-DISABLED %s
+; RUN: echo "v1" > %t
+; RUN: echo "f foo" >> %t
+; RUN: echo "c 0" >> %t
+; RUN: llc < %s -mtriple=x86_64-pc-linux -basic-block-sections=%t  | FileCheck --check-prefix=SOURCE-DRIFT %s
+; RUN: llc < %s -mtriple=x86_64-pc-linux -basic-block-sections=%t -bbsections-detect-source-drift=false | FileCheck --check-prefix=HASH-CHECK-DISABLED %s
 
 define dso_local i32 @foo(i1 zeroext %0, i1 zeroext %1)  !annotation !1 {
   br i1 %0, label %5, label %3