1 files changed, 23 insertions, 7 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCFastISel.cpp b/llvm/lib/Target/PowerPC/PPCFastISel.cpp
index 1de26790651..360fbb61bc5 100644
--- a/llvm/lib/Target/PowerPC/PPCFastISel.cpp
+++ b/llvm/lib/Target/PowerPC/PPCFastISel.cpp
@@ -213,13 +213,29 @@ static Optional<PPC::Predicate> getComparePred(CmpInst::Predicate Pred) {
   switch (Pred) {
     // These are not representable with any single compare.
     case CmpInst::FCMP_FALSE:
+    case CmpInst::FCMP_TRUE:
+    // Major concern about the following 6 cases is NaN result. The comparison
+    // result consists of 4 bits, indicating lt, eq, gt and un (unordered),
+    // only one of which will be set. The result is generated by fcmpu
+    // instruction. However, bc instruction only inspects one of the first 3
+    // bits, so when un is set, bc instruction may jump to to an undesired
+    // place.
+    //
+    // More specifically, if we expect an unordered comparison and un is set, we
+    // expect to always go to true branch; in such case UEQ, UGT and ULT still
+    // give false, which are undesired; but UNE, UGE, ULE happen to give true,
+    // since they are tested by inspecting !eq, !lt, !gt, respectively.
+    //
+    // Similarly, for ordered comparison, when un is set, we always expect the
+    // result to be false. In such case OGT, OLT and OEQ is good, since they are
+    // actually testing GT, LT, and EQ respectively, which are false. OGE, OLE
+    // and ONE are tested through !lt, !gt and !eq, and these are true.
     case CmpInst::FCMP_UEQ:
     case CmpInst::FCMP_UGT:
-    case CmpInst::FCMP_UGE:
     case CmpInst::FCMP_ULT:
-    case CmpInst::FCMP_ULE:
-    case CmpInst::FCMP_UNE:
-    case CmpInst::FCMP_TRUE:
+    case CmpInst::FCMP_OGE:
+    case CmpInst::FCMP_OLE:
+    case CmpInst::FCMP_ONE:
     default:
       return Optional<PPC::Predicate>();
 
@@ -232,7 +248,7 @@ static Optional<PPC::Predicate> getComparePred(CmpInst::Predicate Pred) {
     case CmpInst::ICMP_SGT:
       return PPC::PRED_GT;
 
-    case CmpInst::FCMP_OGE:
+    case CmpInst::FCMP_UGE:
     case CmpInst::ICMP_UGE:
     case CmpInst::ICMP_SGE:
       return PPC::PRED_GE;
@@ -242,12 +258,12 @@ static Optional<PPC::Predicate> getComparePred(CmpInst::Predicate Pred) {
     case CmpInst::ICMP_SLT:
       return PPC::PRED_LT;
 
-    case CmpInst::FCMP_OLE:
+    case CmpInst::FCMP_ULE:
     case CmpInst::ICMP_ULE:
     case CmpInst::ICMP_SLE:
       return PPC::PRED_LE;
 
-    case CmpInst::FCMP_ONE:
+    case CmpInst::FCMP_UNE:
     case CmpInst::ICMP_NE:
       return PPC::PRED_NE;