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Implement constant propogation of PHI instructions like this:
X = phi(0, 0, 0) git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2543 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -5,7 +5,7 @@
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//===----------------------------------------------------------------------===//
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#include "llvm/ConstantHandling.h"
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#include "llvm/Instruction.h"
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#include "llvm/iPHINode.h"
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#include <cmath>
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AnnotationID ConstRules::AID(AnnotationManager::getID("opt::ConstRules",
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@ -15,6 +15,22 @@ AnnotationID ConstRules::AID(AnnotationManager::getID("opt::ConstRules",
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// If successful, the constant result is returned, if not, null is returned.
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//
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Constant *ConstantFoldInstruction(Instruction *I) {
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if (PHINode *PN = dyn_cast<PHINode>(I)) {
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if (PN->getNumIncomingValues() == 0)
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return Constant::getNullValue(PN->getType());
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Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0));
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if (Result == 0) return 0;
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// Handle PHI nodes specially here...
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for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
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if (PN->getIncomingValue(i) != Result)
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return 0; // Not all the same incoming constants...
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// If we reach here, all incoming values are the same constant.
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return Result;
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}
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Constant *Op0 = 0;
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Constant *Op1 = 0;
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