[FuncSpec] Improve estimation of select instruction. #111176
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When propagating a constant to a select instruction we only consider the condition operand as the use. I am extending the logic to consider the true and false values too, in case the condition had been found to be constant in a previous propagation but halted.
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@llvm/pr-subscribers-llvm-transforms Author: Alexandros Lamprineas (labrinea) ChangesWhen propagating a constant to a select instruction we only consider the condition operand as the use. I am extending the logic to consider the true and false values too, in case the condition had been found to be constant in a previous propagation but halted. Full diff: https://github.com/llvm/llvm-project/pull/111176.diff 1 Files Affected:
diff --git a/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp b/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
index 548335d750e33d..7d109af9091479 100644
--- a/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
@@ -423,13 +423,16 @@ Constant *InstCostVisitor::visitGetElementPtrInst(GetElementPtrInst &I) {
Constant *InstCostVisitor::visitSelectInst(SelectInst &I) {
assert(LastVisited != KnownConstants.end() && "Invalid iterator!");
- if (I.getCondition() != LastVisited->first)
- return nullptr;
-
- Value *V = LastVisited->second->isZeroValue() ? I.getFalseValue()
- : I.getTrueValue();
- Constant *C = findConstantFor(V, KnownConstants);
- return C;
+ if (I.getCondition() == LastVisited->first) {
+ Value *V = LastVisited->second->isZeroValue() ? I.getFalseValue()
+ : I.getTrueValue();
+ return findConstantFor(V, KnownConstants);
+ }
+ if (Constant *Condition = findConstantFor(I.getCondition(), KnownConstants))
+ if (I.getTrueValue() == LastVisited->first && Condition->isOneValue() ||
+ I.getFalseValue() == LastVisited->first && Condition->isZeroValue())
+ return LastVisited->second;
+ return nullptr;
}
Constant *InstCostVisitor::visitCastInst(CastInst &I) {
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@llvm/pr-subscribers-function-specialization Author: Alexandros Lamprineas (labrinea) ChangesWhen propagating a constant to a select instruction we only consider the condition operand as the use. I am extending the logic to consider the true and false values too, in case the condition had been found to be constant in a previous propagation but halted. Full diff: https://github.com/llvm/llvm-project/pull/111176.diff 1 Files Affected:
diff --git a/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp b/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
index 548335d750e33d..7d109af9091479 100644
--- a/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
@@ -423,13 +423,16 @@ Constant *InstCostVisitor::visitGetElementPtrInst(GetElementPtrInst &I) {
Constant *InstCostVisitor::visitSelectInst(SelectInst &I) {
assert(LastVisited != KnownConstants.end() && "Invalid iterator!");
- if (I.getCondition() != LastVisited->first)
- return nullptr;
-
- Value *V = LastVisited->second->isZeroValue() ? I.getFalseValue()
- : I.getTrueValue();
- Constant *C = findConstantFor(V, KnownConstants);
- return C;
+ if (I.getCondition() == LastVisited->first) {
+ Value *V = LastVisited->second->isZeroValue() ? I.getFalseValue()
+ : I.getTrueValue();
+ return findConstantFor(V, KnownConstants);
+ }
+ if (Constant *Condition = findConstantFor(I.getCondition(), KnownConstants))
+ if (I.getTrueValue() == LastVisited->first && Condition->isOneValue() ||
+ I.getFalseValue() == LastVisited->first && Condition->isZeroValue())
+ return LastVisited->second;
+ return nullptr;
}
Constant *InstCostVisitor::visitCastInst(CastInst &I) {
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This seems like a worthwhile improvement to the logic here. Might it be useful to have some test coverage for this change? |
* Added surrounding parentheses in condition to fix warning. * Added a unittest.
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When propagating a constant to a select instruction we only consider the condition operand as the use. I am extending the logic to consider the true and false values too, in case the condition had been found to be constant in a previous propagation but halted.