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Implement constant propogation of PHI instructions like this:

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X = phi(0, 0, 0)

llvm-svn: 2543
This commit is contained in:
Chris Lattner 2002-05-07 20:44:59 +00:00
parent 49ac9debec
commit c636f5427b
1 changed files with 17 additions and 1 deletions
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18
lib/VMCore/ConstantHandling.cpp
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@ -5,7 +5,7 @@
//===----------------------------------------------------------------------===//
#include "llvm/ConstantHandling.h"
#include "llvm/Instruction.h"
#include "llvm/iPHINode.h"
#include <cmath>
AnnotationID ConstRules::AID(AnnotationManager::getID("opt::ConstRules",
@ -15,6 +15,22 @@ AnnotationID ConstRules::AID(AnnotationManager::getID("opt::ConstRules",
// If successful, the constant result is returned, if not, null is returned.
//
Constant *ConstantFoldInstruction(Instruction *I) {
if (PHINode *PN = dyn_cast<PHINode>(I)) {
if (PN->getNumIncomingValues() == 0)
return Constant::getNullValue(PN->getType());
Constant *Result = dyn_cast<Constant>(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)
return 0; // Not all the same incoming constants...
// If we reach here, all incoming values are the same constant.
return Result;
}
Constant *Op0 = 0;
Constant *Op1 = 0;