[PowerPC] Use record-form instruction for Less-or-Equal -1 and Greater-or-Equal 1
Currently a record-form instruction is used for comparison of "greater than -1" and "less than 1" by modifying the predicate (e.g. LT 1 into LE 0) in addition to the naive case of comparison against 0.
This patch also enables emitting a record-form instruction for "less than or equal to -1" (i.e. "less than 0") and "greater than or equal to 1" (i.e. "greater than 0") to increase the optimization opportunities.
Differential Revision: https://reviews.llvm.org/D38941
llvm-svn: 316647
diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
index d12610d..7092029 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
@@ -1715,38 +1715,47 @@
else if (MI->getParent() != CmpInstr.getParent())
return false;
else if (Value != 0) {
- // The record-form instructions set CR bit based on signed comparison against 0.
- // We try to convert a compare against 1 or -1 into a compare against 0.
- bool Success = false;
- if (!equalityOnly && MRI->hasOneUse(CRReg)) {
- MachineInstr *UseMI = &*MRI->use_instr_begin(CRReg);
- if (UseMI->getOpcode() == PPC::BCC) {
- PPC::Predicate Pred = (PPC::Predicate)UseMI->getOperand(0).getImm();
- unsigned PredCond = PPC::getPredicateCondition(Pred);
- unsigned PredHint = PPC::getPredicateHint(Pred);
- int16_t Immed = (int16_t)Value;
+ // The record-form instructions set CR bit based on signed comparison
+ // against 0. We try to convert a compare against 1 or -1 into a compare
+ // against 0 to exploit record-form instructions. For example, we change
+ // the condition "greater than -1" into "greater than or equal to 0"
+ // and "less than 1" into "less than or equal to 0".
- // When modyfing the condition in the predicate, we propagate hint bits
- // from the original predicate to the new one.
- if (Immed == -1 && PredCond == PPC::PRED_GT) {
- // We convert "greater than -1" into "greater than or equal to 0",
- // since we are assuming signed comparison by !equalityOnly
- PredsToUpdate.push_back(std::make_pair(&(UseMI->getOperand(0)),
- PPC::getPredicate(PPC::PRED_GE, PredHint)));
- Success = true;
- }
- else if (Immed == 1 && PredCond == PPC::PRED_LT) {
- // We convert "less than 1" into "less than or equal to 0".
- PredsToUpdate.push_back(std::make_pair(&(UseMI->getOperand(0)),
- PPC::getPredicate(PPC::PRED_LE, PredHint)));
- Success = true;
- }
- }
- }
-
- // PPC does not have a record-form SUBri.
- if (!Success)
+ // Since we optimize comparison based on a specific branch condition,
+ // we don't optimize if condition code is used by more than once.
+ if (equalityOnly || !MRI->hasOneUse(CRReg))
return false;
+
+ MachineInstr *UseMI = &*MRI->use_instr_begin(CRReg);
+ if (UseMI->getOpcode() != PPC::BCC)
+ return false;
+
+ PPC::Predicate Pred = (PPC::Predicate)UseMI->getOperand(0).getImm();
+ PPC::Predicate NewPred = Pred;
+ unsigned PredCond = PPC::getPredicateCondition(Pred);
+ unsigned PredHint = PPC::getPredicateHint(Pred);
+ int16_t Immed = (int16_t)Value;
+
+ // When modyfing the condition in the predicate, we propagate hint bits
+ // from the original predicate to the new one.
+ if (Immed == -1 && PredCond == PPC::PRED_GT)
+ // We convert "greater than -1" into "greater than or equal to 0",
+ // since we are assuming signed comparison by !equalityOnly
+ NewPred = PPC::getPredicate(PPC::PRED_GE, PredHint);
+ else if (Immed == -1 && PredCond == PPC::PRED_LE)
+ // We convert "less than or equal to -1" into "less than 0".
+ NewPred = PPC::getPredicate(PPC::PRED_LT, PredHint);
+ else if (Immed == 1 && PredCond == PPC::PRED_LT)
+ // We convert "less than 1" into "less than or equal to 0".
+ NewPred = PPC::getPredicate(PPC::PRED_LE, PredHint);
+ else if (Immed == 1 && PredCond == PPC::PRED_GE)
+ // We convert "greater than or equal to 1" into "greater than 0".
+ NewPred = PPC::getPredicate(PPC::PRED_GT, PredHint);
+ else
+ return false;
+
+ PredsToUpdate.push_back(std::make_pair(&(UseMI->getOperand(0)),
+ NewPred));
}
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