From 71c4035c18a9f008fd2b946c990f0da00754b1a5 Mon Sep 17 00:00:00 2001 From: Philip Reames Date: Tue, 10 Mar 2015 22:52:37 +0000 Subject: If a conditional branch jumps to the same target, remove the condition Given that large parts of inst combine is restricted to instructions which have one use, getting rid of a use on the condition can help the effectiveness of the optimizer. Also, it allows the condition to potentially be deleted by instcombine rather than waiting for another pass. I noticed this completely by accident in another test case. It's not anything that actually came from a real workload. p.s. We should probably do the same thing for switch instructions. Differential Revision: http://reviews.llvm.org/D8220 llvm-svn: 231881 --- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'llvm/lib/Transforms/InstCombine/InstructionCombining.cpp') diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp index 1fe036b5fbb..434d129bf39 100644 --- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp +++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp @@ -2002,6 +2002,15 @@ Instruction *InstCombiner::visitBranchInst(BranchInst &BI) { return &BI; } + // If the condition is irrelevant, remove the use so that other + // transforms on the condition become more effective. + if (BI.isConditional() && + BI.getSuccessor(0) == BI.getSuccessor(1) && + !isa(BI.getCondition())) { + BI.setCondition(UndefValue::get(BI.getCondition()->getType())); + return &BI; + } + // Canonicalize fcmp_one -> fcmp_oeq FCmpInst::Predicate FPred; Value *Y; if (match(&BI, m_Br(m_FCmp(FPred, m_Value(X), m_Value(Y)), -- cgit v1.2.3