Index: llvm/trunk/include/llvm/Target/TargetSchedule.td
===================================================================
--- llvm/trunk/include/llvm/Target/TargetSchedule.td
+++ llvm/trunk/include/llvm/Target/TargetSchedule.td
@@ -281,10 +281,9 @@
 // ProcResources indicates the set of resources consumed by the write.
 // Optionally, ResourceCycles indicates the number of cycles the
 // resource is consumed. Each ResourceCycles item is paired with the
-// ProcResource item at the same position in its list. Since
-// ResourceCycles are rarely specialized, the list may be
-// incomplete. By default, resources are consumed for a single cycle,
-// regardless of latency, which models a fully pipelined processing
+// ProcResource item at the same position in its list. ResourceCycles
+// can be `[]`: in that case, all resources are consumed for a single
+// cycle, regardless of latency, which models a fully pipelined processing
 // unit. A value of 0 for ResourceCycles means that the resource must
 // be available but is not consumed, which is only relevant for
 // unbuffered resources.
Index: llvm/trunk/lib/Target/AArch64/AArch64SchedThunderX2T99.td
===================================================================
--- llvm/trunk/lib/Target/AArch64/AArch64SchedThunderX2T99.td
+++ llvm/trunk/lib/Target/AArch64/AArch64SchedThunderX2T99.td
@@ -416,7 +416,7 @@
 // Address generation
 def : WriteRes<WriteI,       [THX2T99I012]> {
   let Latency = 1;
-  let ResourceCycles = [1, 3];
+  let ResourceCycles = [1];
   let NumMicroOps = 2;
 }
 
@@ -438,7 +438,7 @@
 // ALU, extend and/or shift
 def : WriteRes<WriteISReg,   [THX2T99I012]> {
   let Latency = 2;
-  let ResourceCycles = [2, 3];
+  let ResourceCycles = [2];
   let NumMicroOps = 2;
 }
 
@@ -457,7 +457,7 @@
 
 def : WriteRes<WriteIEReg,   [THX2T99I012]> {
   let Latency = 1;
-  let ResourceCycles = [1, 3];
+  let ResourceCycles = [1];
   let NumMicroOps = 2;
 }
 
@@ -500,14 +500,14 @@
 // Latency range of 13-23/13-39.
 def : WriteRes<WriteID32,    [THX2T99I1]> {
   let Latency = 39;
-  let ResourceCycles = [13, 39];
+  let ResourceCycles = [39];
   let NumMicroOps = 4;
 }
 
 // Divide, X-form
 def : WriteRes<WriteID64,    [THX2T99I1]> {
   let Latency = 23;
-  let ResourceCycles = [13, 23];
+  let ResourceCycles = [23];
   let NumMicroOps = 4;
 }
 
@@ -1252,7 +1252,7 @@
 def : WriteRes<WriteV, [THX2T99F01]> {
   let Latency = 7;
   let NumMicroOps = 4;
-  let ResourceCycles = [4, 23];
+  let ResourceCycles = [4];
 }
 
 // ASIMD arith, reduce, 4H/4S
Index: llvm/trunk/utils/TableGen/SubtargetEmitter.cpp
===================================================================
--- llvm/trunk/utils/TableGen/SubtargetEmitter.cpp
+++ llvm/trunk/utils/TableGen/SubtargetEmitter.cpp
@@ -941,8 +941,7 @@
 void SubtargetEmitter::ExpandProcResources(RecVec &PRVec,
                                            std::vector<int64_t> &Cycles,
                                            const CodeGenProcModel &PM) {
-  // Default to 1 resource cycle.
-  Cycles.resize(PRVec.size(), 1);
+  assert(PRVec.size() == Cycles.size() && "failed precondition");
   for (unsigned i = 0, e = PRVec.size(); i != e; ++i) {
     Record *PRDef = PRVec[i];
     RecVec SubResources;
@@ -1111,6 +1110,21 @@
         std::vector<int64_t> Cycles =
           WriteRes->getValueAsListOfInts("ResourceCycles");
 
+        if (Cycles.empty()) {
+          // If ResourceCycles is not provided, default to one cycle per
+          // resource.
+          Cycles.resize(PRVec.size(), 1);
+        } else if (Cycles.size() != PRVec.size()) {
+          // If ResourceCycles is provided, check consistency.
+          PrintFatalError(
+              WriteRes->getLoc(),
+              Twine("Inconsistent resource cycles: !size(ResourceCycles) != "
+                    "!size(ProcResources): ")
+                  .concat(Twine(PRVec.size()))
+                  .concat(" vs ")
+                  .concat(Twine(Cycles.size())));
+        }
+
         ExpandProcResources(PRVec, Cycles, ProcModel);
 
         for (unsigned PRIdx = 0, PREnd = PRVec.size();