[PATCH] D72908: [BasicBlock] fix looping in getPostdominatingDeoptimizeCall

[Fedor Sergeev via Phabricator via llvm-commits]

fedor.sergeev updated this revision to Diff 238720.
fedor.sergeev added a comment.

adding CHECK-LABEL to the test so it passes with lit


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D72908/new/

https://reviews.llvm.org/D72908

Files:
  llvm/lib/IR/BasicBlock.cpp
  llvm/test/Transforms/LoopPredication/unswitch-exit-loop.ll


Index: llvm/test/Transforms/LoopPredication/unswitch-exit-loop.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/LoopPredication/unswitch-exit-loop.ll
@@ -0,0 +1,55 @@
+; RUN: opt < %s -loop-predication -S | FileCheck %s
+
+;; This is a simplified copy of @unswitch_exit_form test that should trigger loop-predication
+;; activity and properly bail out when discovering that widenable check does not lead to deopt.
+;;
+;; Error checking is rather silly here - it should pass compilation successfully,
+;; in bad case it will just timeout.
+;;
+define i32 @unswitch_exit_form_with_endless_loop(i32* %array, i32 %length, i32 %n, i1 %cond_0) {
+; CHECK-LABEL: @unswitch_exit_form_with_endless_loop
+entry:
+  %widenable_cond = call i1 @llvm.experimental.widenable.condition()
+  %exiplicit_guard_cond = and i1 %cond_0, %widenable_cond
+  br i1 %exiplicit_guard_cond, label %loop.preheader, label %not_really_a_deopt, !prof !0
+
+not_really_a_deopt:
+  br label %looping
+
+looping:
+  ;; synthetic corner case that demonstrates the need for more careful traversal
+  ;; of unique successors when walking through the exit for profitability checks.
+  br label %looping
+
+loop.preheader:
+  br label %loop
+
+loop:
+  %loop.acc = phi i32 [ %loop.acc.next, %guarded ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %guarded ], [ 0, %loop.preheader ]
+  %within.bounds = icmp ult i32 %i, %length
+  br i1 %within.bounds, label %guarded, label %not_really_a_deopt, !prof !0
+
+guarded:
+  %i.i64 = zext i32 %i to i64
+  %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+  %array.i = load i32, i32* %array.i.ptr, align 4
+  store i32 0, i32* %array.i.ptr
+  %loop.acc.next = add i32 %loop.acc, %array.i
+  %i.next = add nuw i32 %i, 1
+  %continue = icmp ult i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ %loop.acc.next, %guarded ]
+  ret i32 %result
+}
+
+declare void @unknown()
+
+declare i1 @llvm.experimental.widenable.condition()
+declare i32 @llvm.experimental.deoptimize.i32(...)
+
+!0 = !{!"branch_weights", i32 1048576, i32 1}
+!1 = !{i32 1, i32 -2147483648}
+!2 = !{i32 0, i32 50}
Index: llvm/lib/IR/BasicBlock.cpp
===================================================================
--- llvm/lib/IR/BasicBlock.cpp
+++ llvm/lib/IR/BasicBlock.cpp
@@ -195,8 +195,13 @@
 
 const CallInst *BasicBlock::getPostdominatingDeoptimizeCall() const {
   const BasicBlock* BB = this;
-  while (BB->getUniqueSuccessor())
-    BB = BB->getUniqueSuccessor();
+  SmallPtrSet<const BasicBlock *, 8> Visited;
+  Visited.insert(BB);
+  while (auto *Succ = BB->getUniqueSuccessor()) {
+    if (!Visited.insert(Succ).second)
+      return nullptr;
+    BB = Succ;
+  }
   return BB->getTerminatingDeoptimizeCall();
 }
 


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