[llvm] r216911 - LICM: Don't crash when an instruction is used by an unreachable BB

[David Majnemer]

Author: majnemer
Date: Tue Sep  2 11:22:00 2014
New Revision: 216911

URL: http://llvm.org/viewvc/llvm-project?rev=216911&view=rev
Log:
LICM: Don't crash when an instruction is used by an unreachable BB

Summary:
BBs might contain non-LCSSA'd values after the LCSSA pass is run if they
are unreachable from the entry block.

Normally, the users of the instruction would be PHIs but the unreachable
BBs have normal users; rewrite their uses to be undef values.

An alternative fix could involve fixing this at LCSSA but that would
require this invariant to hold after subsequent transforms.  If a BB
created an unreachable block, they would be in violation of this.

This fixes PR19798.

Differential Revision: http://reviews.llvm.org/D5146

Added:
    llvm/trunk/test/Transforms/LICM/PR19798.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/LICM.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/LICM.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LICM.cpp?rev=216911&r1=216910&r2=216911&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LICM.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LICM.cpp Tue Sep  2 11:22:00 2014
@@ -597,8 +597,13 @@ void LICM::sink(Instruction &I) {
   // 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();
+    if (!DT->isReachableFromEntry(User->getParent())) {
+      User->replaceUsesOfWith(&I, UndefValue::get(I.getType()));
+      continue;
+    }
     // The user must be a PHI node.
-    PHINode *PN = cast<PHINode>(I.user_back());
+    PHINode *PN = cast<PHINode>(User);
 
     BasicBlock *ExitBlock = PN->getParent();
     assert(ExitBlockSet.count(ExitBlock) &&

Added: llvm/trunk/test/Transforms/LICM/PR19798.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LICM/PR19798.ll?rev=216911&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/LICM/PR19798.ll (added)
+++ llvm/trunk/test/Transforms/LICM/PR19798.ll Tue Sep  2 11:22:00 2014
@@ -0,0 +1,22 @@
+; RUN: opt -licm -S < %s | FileCheck %s
+
+define void @f() {
+; CHECK-LABEL: @f(
+entry:
+  br label %bb0
+
+bb0:
+  %tobool7 = icmp eq i1 undef, undef
+  br label %bb1
+
+bb1:
+  br i1 undef, label %bb0, label %bb0
+
+unreachable:
+; CHECK-LABEL: unreachable:
+; CHECK:   br i1 undef, label %unreachable, label %unreachable
+  br i1 %tobool7, label %unreachable, label %unreachable
+
+bb3:
+  unreachable
+}