From c0362d5c6e0066c741bce056a65d8b4c026de19f Mon Sep 17 00:00:00 2001 From: Duncan Sands Date: Sun, 14 Nov 2010 12:53:18 +0000 Subject: [PATCH] Boost the power of phi node constant folding slightly: if all operands are the phi node itself or undef, then return undef. This logic already existed at a higher level so in practice it shouldn't make the slightest difference. Note that this code could be replaced by a call to PN->hasConstantValue(). However since we bail out the moment we see a non-constant operand, it is more efficient to have a specialized version of that logic. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119041 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Analysis/ConstantFolding.cpp | 30 ++++++++++++++++++------------ 1 file changed, 18 insertions(+), 12 deletions(-) diff --git a/lib/Analysis/ConstantFolding.cpp b/lib/Analysis/ConstantFolding.cpp index f512dd69a33..f2e89a773e7 100644 --- a/lib/Analysis/ConstantFolding.cpp +++ b/lib/Analysis/ConstantFolding.cpp @@ -695,20 +695,26 @@ static Constant *SymbolicallyEvaluateGEP(Constant *const *Ops, unsigned NumOps, /// instructions like loads and stores, which have no constant expression form. /// Constant *llvm::ConstantFoldInstruction(Instruction *I, const TargetData *TD) { + // Handle PHI nodes specially here... if (PHINode *PN = dyn_cast(I)) { - if (PN->getNumIncomingValues() == 0) - return UndefValue::get(PN->getType()); - - Constant *Result = dyn_cast(PN->getIncomingValue(0)); - if (Result == 0) return 0; - - // Handle PHI nodes specially here... - for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) - if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN) - return 0; // Not all the same incoming constants... + Constant *CommonValue = 0; + + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + Value *Incoming = PN->getIncomingValue(i); + // If the incoming value is equal to the phi node itself or is undef then + // skip it. + if (Incoming == PN || isa(Incoming)) + continue; + // If the incoming value is not a constant, or is a different constant to + // the one we saw previously, then give up. + Constant *C = dyn_cast(Incoming); + if (!C || (CommonValue && C != CommonValue)) + return 0; + CommonValue = C; + } - // If we reach here, all incoming values are the same constant. - return Result; + // If we reach here, all incoming values are the same constant or undef. + return CommonValue ? CommonValue : UndefValue::get(PN->getType()); } // Scan the operand list, checking to see if they are all constants, if so, -- 2.34.1