llvm-c-test avoid calling malloc(0)

[andusy]

Summary

As explained in D63668, malloc(0) could return a null pointer. llvm-c-test does not handle this case correctly. Instead of calling malloc(0), avoid the operation altogether.

[hubert.reinterpretcast]

For a generic tool, this seems to be an okay fix; however, this is an API test driver. I would like to hear from other reviewers as to whether there is an intent to test the API for the AttrCount == 0 case. If there is, then I believe that allocation should not be attempted, and the API should work with a null pointer.

[hubert.reinterpretcast]

To preserve exercising of the list getter when the count is zero, I suggest:

int AttrCount = /*...*/;
LLVMAttributeRef *Attrs = 0;
if (AttrCount) {
  Attrs = /*...*/;
  assert(Attrs);
}
LLVMGet/*...*/;
free(Attrs);

Even on systems where malloc(0) does not return a null pointer, the getter functions could not have safely accessed an object via said pointer.

[andusy]

Update to call LLVMGetAttributesAtIndex even when AttrCount is 0.

[hubert.reinterpretcast]

Thanks @andusy; this LGTM. I believe that you have had a good number of patches committed into the project already (rC356060, rC360900, rL364322, rC364462). Please go ahead with requesting commit access, and commit this patch when you are ready.

llvm/tools/llvm-c-test/attributes.c

int llvm_test_function_attributes(void) {
 
   LLVMValueRef F = LLVMGetFirstFunction(M);
   while (F) {
     // Read attributes
     int Idx, ParamCount;
     for (Idx = LLVMAttributeFunctionIndex, ParamCount = LLVMCountParams(F);
          Idx <= ParamCount; ++Idx) {
       int AttrCount = LLVMGetAttributeCountAtIndex(F, Idx);
+      if (AttrCount) {
         LLVMAttributeRef *Attrs =
             (LLVMAttributeRef *)malloc(AttrCount * sizeof(LLVMAttributeRef));
         assert(Attrs);
         LLVMGetAttributesAtIndex(F, Idx, Attrs);
         free(Attrs);
       }
+    }
     F = LLVMGetNextFunction(F);
   }
 
   LLVMDisposeModule(M);
 
   return 0;
 }
 
for (BB = LLVMGetFirstBasicBlock(F); BB; BB = LLVMGetNextBasicBlock(BB)) {
       for (I = LLVMGetFirstInstruction(BB); I; I = LLVMGetNextInstruction(I)) {
         if (LLVMIsACallInst(I)) {
           // Read attributes
           int Idx, ParamCount;
           for (Idx = LLVMAttributeFunctionIndex,
               ParamCount = LLVMCountParams(F);
                Idx <= ParamCount; ++Idx) {
             int AttrCount = LLVMGetCallSiteAttributeCount(I, Idx);
+            if (AttrCount) {
               LLVMAttributeRef *Attrs = (LLVMAttributeRef *)malloc(
                   AttrCount * sizeof(LLVMAttributeRef));
               assert(Attrs);
               LLVMGetCallSiteAttributes(I, Idx, Attrs);
               free(Attrs);
             }
           }
         }
       }
+    }
 
     F = LLVMGetNextFunction(F);
   }
 
   LLVMDisposeModule(M);
 
   return 0;
 }