IRGen: Fix crash when normal conformance fixes generic parameter to concrete type

This can probably be handled better elsewhere, but this is
reasonable enough for now.

Fixes rdar://146123129.

Author: slavapestov

lib/IRGen/GenProto.cpp

@@ -1257,16 +1257,16 @@ emitConditionalConformancesBuffer(IRGenFunction &IGF,
 }
 
 static llvm::Value *emitWitnessTableAccessorCall(
-    IRGenFunction &IGF, const ProtocolConformance *conformance,
+    IRGenFunction &IGF, CanType conformingType,
+    const ProtocolConformance *conformance,
     llvm::Value **srcMetadataCache) {
   auto conformanceDescriptor =
     IGF.IGM.getAddrOfProtocolConformanceDescriptor(
                                              conformance->getRootConformance());
 
   // Emit the source metadata if we haven't yet.
   if (!*srcMetadataCache) {
-    *srcMetadataCache = IGF.emitAbstractTypeMetadataRef(
-      conformance->getType()->getCanonicalType());
+    *srcMetadataCache = IGF.emitAbstractTypeMetadataRef(conformingType);
   }
 
   auto conditionalTables =
@@ -1290,8 +1290,8 @@ static llvm::Value *emitWitnessTableAccessorCall(
 /// given type.
 static llvm::Function *
 getWitnessTableLazyAccessFunction(IRGenModule &IGM,
+                                  CanType conformingType,
                                   const ProtocolConformance *conformance) {
-  auto conformingType = conformance->getType()->getCanonicalType();
   assert(!conformingType->hasArchetype());
 
   auto rootConformance = conformance->getRootNormalConformance();
@@ -1315,7 +1315,7 @@ getWitnessTableLazyAccessFunction(IRGenModule &IGM,
       [&](IRGenFunction &IGF, Explosion &params) {
         llvm::Value *conformingMetadataCache = nullptr;
         return MetadataResponse::forComplete(emitWitnessTableAccessorCall(
-            IGF, conformance, &conformingMetadataCache));
+            IGF, conformingType, conformance, &conformingMetadataCache));
       });
 
   return accessor;
@@ -1414,16 +1414,23 @@ class AccessorConformanceInfo : public ConformanceInfo {
 
   llvm::Value *getTable(IRGenFunction &IGF,
                         llvm::Value **typeMetadataCache) const override {
+    auto conformingType = Conformance->getType()->getCanonicalType();
+
+    if (isa<NormalProtocolConformance>(Conformance)) {
+      conformingType = conformingType->getReducedType(
+        Conformance->getGenericSignature());
+    }
+
     // If we're looking up a dependent type, we can't cache the result.
-    if (Conformance->getType()->hasArchetype() ||
-        Conformance->getType()->hasDynamicSelfType()) {
-      return emitWitnessTableAccessorCall(IGF, Conformance,
+    if (conformingType->hasArchetype() ||
+        conformingType->hasDynamicSelfType()) {
+      return emitWitnessTableAccessorCall(IGF, conformingType, Conformance,
                                           typeMetadataCache);
     }
 
     // Otherwise, call a lazy-cache function.
     auto accessor =
-      getWitnessTableLazyAccessFunction(IGF.IGM, Conformance);
+      getWitnessTableLazyAccessFunction(IGF.IGM, conformingType, Conformance);
     llvm::CallInst *call =
         IGF.Builder.CreateCall(accessor->getFunctionType(), accessor, {});
     call->setCallingConv(IGF.IGM.DefaultCC);

test/IRGen/rdar146123129.swift

@@ -0,0 +1,26 @@
+// RUN: %target-swift-frontend -emit-ir -O -enable-library-evolution %s
+// REQUIRES: objc_interop
+
+import Foundation
+
+extension Measurement: Strideable where UnitType == UnitLength {
+    public func advanced(by n: Double) -> Measurement<UnitLength> {
+        return Self.init(value: value + n, unit: unit)
+    }
+    
+    public func distance(to other: Measurement<UnitLength>) -> Double {
+        return other.value - value
+    }
+}
+public func test(_ gridHalfSizeInLabelSpacingUnits: Measurement<UnitLength>, _ value: Double, _ orientation: Bool) {
+  let origin = Measurement(value: 0, unit: UnitLength.meters)
+
+  @inline(never)
+  func addLabelMeshForLine(startingAt startPositionMeasurement: Measurement<UnitLength>) {
+      print(startPositionMeasurement)
+  }
+
+  for startPositionMeasurement in stride(from: origin, through: gridHalfSizeInLabelSpacingUnits, by: value) {
+      addLabelMeshForLine(startingAt: startPositionMeasurement)
+  }
+}