[llvm-commits] CVS: llvm/lib/Transforms/Scalar/InstructionCombining.cpp
Chris Lattner
sabre at nondot.org
Sun Jan 14 23:30:21 PST 2007
Changes in directory llvm/lib/Transforms/Scalar:
InstructionCombining.cpp updated: 1.599 -> 1.600
---
Log message:
Implement InstCombine/phi.ll:test7, deletion of trivial value loops for
induction variables.
---
Diffs of the changes: (+16 -2)
InstructionCombining.cpp | 18 ++++++++++++++++--
1 files changed, 16 insertions(+), 2 deletions(-)
Index: llvm/lib/Transforms/Scalar/InstructionCombining.cpp
diff -u llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.599 llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.600
--- llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.599 Mon Jan 15 01:02:54 2007
+++ llvm/lib/Transforms/Scalar/InstructionCombining.cpp Mon Jan 15 01:30:06 2007
@@ -7595,13 +7595,27 @@
// If this is a trivial cycle in the PHI node graph, remove it. Basically, if
// this PHI only has a single use (a PHI), and if that PHI only has one use (a
// PHI)... break the cycle.
- if (PN.hasOneUse())
- if (PHINode *PU = dyn_cast<PHINode>(PN.use_back())) {
+ if (PN.hasOneUse()) {
+ Instruction *PHIUser = cast<Instruction>(PN.use_back());
+ if (PHINode *PU = dyn_cast<PHINode>(PHIUser)) {
std::set<PHINode*> PotentiallyDeadPHIs;
PotentiallyDeadPHIs.insert(&PN);
if (DeadPHICycle(PU, PotentiallyDeadPHIs))
return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
}
+
+ // If this phi has a single use, and if that use just computes a value for
+ // the next iteration of a loop, delete the phi. This occurs with unused
+ // induction variables, e.g. "for (int j = 0; ; ++j);". Detecting this
+ // common case here is good because the only other things that catch this
+ // are induction variable analysis (sometimes) and ADCE, which is only run
+ // late.
+ if (PHIUser->hasOneUse() &&
+ (isa<BinaryOperator>(PHIUser) || isa<GetElementPtrInst>(PHIUser)) &&
+ PHIUser->use_back() == &PN) {
+ return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
+ }
+ }
return 0;
}
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