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
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 1fe036b..434d129 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2002,6 +2002,15 @@
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<UndefValue>(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)),