[PATCH] D125766: [llvm-reduce] improve bb removal

[Markus Lavin via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rGbb8e02325ffc: llvm-reduce: improve basic-blocks removal pass (authored by markus).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D125766/new/

https://reviews.llvm.org/D125766

Files:
  llvm/test/tools/llvm-reduce/remove-bbs-sequence.ll
  llvm/test/tools/llvm-reduce/remove-bbs-sequence.py
  llvm/tools/llvm-reduce/deltas/ReduceBasicBlocks.cpp


Index: llvm/tools/llvm-reduce/deltas/ReduceBasicBlocks.cpp
===================================================================
--- llvm/tools/llvm-reduce/deltas/ReduceBasicBlocks.cpp
+++ llvm/tools/llvm-reduce/deltas/ReduceBasicBlocks.cpp
@@ -47,6 +47,19 @@
   Term->eraseFromParent();
 
   if (ChunkSuccessors.empty()) {
+    // Scan forward in BB list to try find a block that is kept.
+    Function &F = *BB.getParent();
+    Function::iterator FI = BB.getIterator();
+    FI++;
+    while (FI != F.end()) {
+      auto &FIB = *FI;
+      if (BBsToKeep.count(&FIB) && !isa<PHINode>(FIB.begin())) {
+        BranchInst::Create(&FIB, &BB);
+        return;
+      }
+      FI++;
+    }
+    // If that fails then resort to replacing with a ret.
     auto *FnRetTy = BB.getParent()->getReturnType();
     ReturnInst::Create(BB.getContext(),
                        FnRetTy->isVoidTy() ? nullptr : UndefValue::get(FnRetTy),
Index: llvm/test/tools/llvm-reduce/remove-bbs-sequence.py
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-reduce/remove-bbs-sequence.py
@@ -0,0 +1,15 @@
+import subprocess
+import sys
+
+opt = subprocess.run( [ 'opt', '-passes=print<loops>','-disable-output', sys.argv[1]], stdout=subprocess.PIPE, stderr=subprocess.PIPE )
+
+stdout = opt.stdout.decode()
+
+pattern = 'Loop at depth 1 containing'
+
+if (pattern in opt.stderr.decode()):
+  print('This is interesting!')
+  sys.exit(0)
+else:
+  print('This is NOT interesting!')
+  sys.exit(1)
Index: llvm/test/tools/llvm-reduce/remove-bbs-sequence.ll
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-reduce/remove-bbs-sequence.ll
@@ -0,0 +1,30 @@
+; RUN: llvm-reduce --delta-passes=basic-blocks --test %python --test-arg %p/remove-bbs-sequence.py %s -o %t
+; RUN: cat %t | FileCheck %s
+
+; The interestingness test is that the CFG contains a loop. Verify that the
+; unnecessary bb2 and bb3 are removed while still maintaining a loop.
+
+define void @main() {
+  bb0:
+    br label %bb1
+  bb1:
+    br label %bb2
+  bb2:
+    br label %bb3
+  bb3:
+    %phi = phi i32 [ undef, %bb2 ]
+    br label %bb4
+  bb4:
+    br label %bb1
+}
+
+; CHECK:define void @main() {
+; CHECK-NEXT: bb0:
+; CHECK-NEXT:   br label %bb1
+; CHECK-EMPTY:
+; CHECK-NEXT: bb1:
+; CHECK-NEXT:   br label %bb4
+; CHECK-EMPTY:
+; CHECK-NEXT: bb4:
+; CHECK-NEXT:   br label %bb1
+; CHECK-NEXT:}


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