[PATCH] D34135: [JumpThreading] Use DT to avoid processing dead blocks

[Mikael Holmén via Phabricator via llvm-commits]

uabelho updated this revision to Diff 130139.
uabelho retitled this revision from "[LVI] Add initial result to avoid infinite getValueFromCondition recursion" to "[JumpThreading] Use DT to avoid processing dead blocks".
uabelho edited the summary of this revision.
uabelho added a comment.

Use DT directly in JumpThreading instead of hacking LVI.


https://reviews.llvm.org/D34135

Files:
  lib/Transforms/Scalar/JumpThreading.cpp
  test/Transforms/JumpThreading/PR33357-lvi-recursion.ll


Index: test/Transforms/JumpThreading/PR33357-lvi-recursion.ll
===================================================================
--- /dev/null
+++ test/Transforms/JumpThreading/PR33357-lvi-recursion.ll
@@ -0,0 +1,44 @@
+; RUN: opt -S -jump-threading -verify -o - %s | FileCheck %s
+
+; Don't enter infinite recursion in LazyValueInfo.cpp
+
+ at a = external global i16, align 1
+
+define void @f(i32 %p1) {
+bb0:
+  %0 = icmp eq i32 %p1, 0
+  br i1 undef, label %bb6, label %bb1
+
+bb1:                                         ; preds = %bb0
+  br label %bb2
+
+bb2:                                         ; preds = %bb4, %bb1
+  %1 = phi i1 [ %0, %bb1 ], [ %2, %bb4 ]
+  %2 = and i1 %1, undef
+  br i1 %2, label %bb3, label %bb4
+
+bb3:                                         ; preds = %bb2
+  store i16 undef, i16* @a, align 1
+  br label %bb4
+
+bb4:                                         ; preds = %bb3, %bb2
+  br i1 %0, label %bb2, label %bb5
+
+bb5:                                         ; preds = %bb4
+  unreachable
+
+bb6:                                         ; preds = %bb0
+  ret void
+}
+
+; The
+;  br i1 undef, label %bb6, label %bb1
+; is replaced by
+;  br label %bb6
+; and the rest of the function is unreachable from entry and jump-threading
+; shouldn't even ask LazyValueInfo about things in the dead blocks.
+
+; CHECK:      define void @f(i32 %p1) {
+; CHECK-NEXT: bb6:
+; CHECK-NEXT:   %0 = icmp eq i32 %p1, 0
+; CHECK-NEXT:   ret void
\ No newline at end of file
Index: lib/Transforms/Scalar/JumpThreading.cpp
===================================================================
--- lib/Transforms/Scalar/JumpThreading.cpp
+++ lib/Transforms/Scalar/JumpThreading.cpp
@@ -946,10 +946,9 @@
 /// ProcessBlock - If there are any predecessors whose control can be threaded
 /// through to a successor, transform them now.
 bool JumpThreadingPass::ProcessBlock(BasicBlock *BB) {
-  // If the block is trivially dead, just return and let the caller nuke it.
+  // If the block is dead, just return and let the caller nuke it.
   // This simplifies other transformations.
-  if (DDT->pendingDeletedBB(BB) ||
-      (pred_empty(BB) && BB != &BB->getParent()->getEntryBlock()))
+  if (DDT->pendingDeletedBB(BB) || !DDT->flush().isReachableFromEntry(BB))
     return false;
 
   // If this block has a single predecessor, and if that pred has a single


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