[Polly] [GPUJIT] Set min size to 1 on allocation calls.

[bollu]

Summary

All cuda allocation functions fail on size 0 allocations. So, make sure that
we allocate a minimum of size 1.

[bollu]

• [NFC] document why we care about size 0 allocs

[bollu]

@singam-sanjay Review please.

[bollu]

• [NFC] remove TODO with actual code

[grosser]

LGTM

tools/GPURuntime/GPUJIT.c

 #include <dlfcn.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
 #include <unistd.h>
 
 static int DebugMode;
 static int CacheMode;
+#define max(x, y) ((x) > (y) ? (x) : (y))
 
 static PollyGPURuntime Runtime = RUNTIME_NONE;
 
 static void debug_print(const char *format, ...) {
   if (!DebugMode)
     return;
 
   va_list args;
if (isManagedPtr(mem)) {
     }
     return;
   } else {
     free(mem);
   }
 }
 
 void *polly_mallocManaged(size_t size) {
+  
+  // TODO: print warning message if size == 0 if POLLY_DEBUG=1, so that
+  // the user knows that this behaviour is kicking in.
+  size = max(size, 1);
+  polly_initContextCUDA();
   dump_function();
   void *a;
   if (cudaMallocManaged(&a, size, cudaMemAttachGlobal) != cudaSuccess) {
     fprintf(stderr, "cudaMallocManaged failed for size: %zu\n", size);
     exit(-1);
   }
   addManagedPtr(a);
   return a;
 }
 
 static void freeDeviceMemoryCUDA(PollyGPUDevicePtr *Allocation) {
   dump_function();
   CUDADevicePtr *DevPtr = (CUDADevicePtr *)Allocation->DevicePtr;
   CuMemFreeFcnPtr((CUdeviceptr)DevPtr->Cuda);
   free(DevPtr);
   free(Allocation);
 }
 
 static PollyGPUDevicePtr *allocateMemoryForDeviceCUDA(long MemSize) {
+  MemSize = max(MemSize, 1);
   dump_function();
 
   PollyGPUDevicePtr *DevData = malloc(sizeof(PollyGPUDevicePtr));
   if (DevData == 0) {
     fprintf(stderr, "Allocate memory for GPU device memory pointer failed.\n");
     exit(-1);
   }
   DevData->DevicePtr = (CUDADevicePtr *)malloc(sizeof(CUDADevicePtr));