[PATCH] D10903: [LICM] Replace incoming values with undef if the incoming BB is unreachable

[David Majnemer]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL241987: [LICM] Don't try to sink values out of loops without any exits (authored by majnemer).

Changed prior to commit:
  http://reviews.llvm.org/D10903?vs=28967&id=29516#toc

Repository:
  rL LLVM

http://reviews.llvm.org/D10903

Files:
  llvm/trunk/lib/Transforms/Scalar/LICM.cpp
  llvm/trunk/test/Transforms/LICM/PR24013.ll

Index: llvm/trunk/test/Transforms/LICM/PR24013.ll
===================================================================
--- llvm/trunk/test/Transforms/LICM/PR24013.ll
+++ llvm/trunk/test/Transforms/LICM/PR24013.ll
@@ -0,0 +1,19 @@
+; RUN: opt -licm -S < %s | FileCheck %s
+
+define void @f(i1 zeroext %p1) {
+; CHECK-LABEL: @f(
+entry:
+  br label %lbl
+
+lbl.loopexit:                                     ; No predecessors!
+  br label %lbl
+
+lbl:                                              ; preds = %lbl.loopexit, %entry
+  %phi = phi i32 [ %conv, %lbl.loopexit ], [ undef, %entry ]
+; CHECK: phi i32 [ undef, {{.*}} ], [ undef
+  br label %if.then.5
+
+if.then.5:                                        ; preds = %if.then.5, %lbl
+  %conv = zext i1 undef to i32
+  br label %if.then.5
+}
Index: llvm/trunk/lib/Transforms/Scalar/LICM.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/LICM.cpp
+++ llvm/trunk/lib/Transforms/Scalar/LICM.cpp
@@ -602,14 +602,25 @@
   // PHI nodes in exit blocks due to LCSSA form. Just RAUW them with clones of
   // the instruction.
   while (!I.use_empty()) {
-    Instruction *User = I.user_back();
+    Value::user_iterator UI = I.user_begin();
+    auto *User = cast<Instruction>(*UI);
     if (!DT->isReachableFromEntry(User->getParent())) {
       User->replaceUsesOfWith(&I, UndefValue::get(I.getType()));
       continue;
     }
     // The user must be a PHI node.
     PHINode *PN = cast<PHINode>(User);
 
+    // Surprisingly, instructions can be used outside of loops without any
+    // exits.  This can only happen in PHI nodes if the incoming block is
+    // unreachable.
+    Use &U = UI.getUse();
+    BasicBlock *BB = PN->getIncomingBlock(U);
+    if (!DT->isReachableFromEntry(BB)) {
+      U = UndefValue::get(I.getType());
+      continue;
+    }
+
     BasicBlock *ExitBlock = PN->getParent();
     assert(ExitBlockSet.count(ExitBlock) &&
            "The LCSSA PHI is not in an exit block!");


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