From 1593ac259db20a5ed71b241c5e9c2796f5d34044 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Tue, 2 Aug 2005 03:24:05 +0000 Subject: [PATCH] This code was very close, but not quite right. It did not take into consideration the case where a reference in an unreachable block could occur. This fixes Transforms/SimplifyCFG/2005-08-01-PHIUpdateFail.ll, something I ran into while bugpoint'ing another pass. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22584 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Utils/SimplifyCFG.cpp | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp index 6a3b803cbdb..c060127e2c0 100644 --- a/lib/Transforms/Utils/SimplifyCFG.cpp +++ b/lib/Transforms/Utils/SimplifyCFG.cpp @@ -894,9 +894,16 @@ bool llvm::SimplifyCFG(BasicBlock *BB) { // Move all PHI nodes in BB to Succ if they are alive, otherwise // delete them. while (PHINode *PN = dyn_cast(&BB->front())) - if (PN->use_empty()) - BB->getInstList().erase(BB->begin()); // Nuke instruction. - else { + if (PN->use_empty() || Succ->getSinglePredecessor() == 0) { + // We can only move the PHI node into Succ if BB dominates Succ. + // Since BB only has a single successor (Succ), the PHI nodes + // will dominate Succ, unless Succ has multiple predecessors. In + // this case, the PHIs are either dead, or have references in dead + // blocks. In either case, we can just remove them. + if (!PN->use_empty()) // Uses in dead block? + PN->replaceAllUsesWith(UndefValue::get(PN->getType())); + PN->eraseFromParent(); // Nuke instruction. + } else { // The instruction is alive, so this means that Succ must have // *ONLY* had BB as a predecessor, and the PHI node is still valid // now. Simply move it into Succ, because we know that BB