[llvm-diff] Check for recursive initializers

[void]

Summary

We need to check for recursive initializers in the "ConstantStruct"
case.

[void]

Friendly ping.

[void]

Another ping. :-)

[rjmccall]

Uh-oh, the pings are getting less friendly. :)

LGTM

[void]

In D105616#2894620, @rjmccall wrote:

Uh-oh, the pings are getting less friendly. :)

LGTM

The beatings will continue until LGTM!!

X-D

llvm/test/tools/llvm-diff/initializers.ll

 %struct.list_head = type { %struct.list_head*, %struct.list_head* }
 
 @vmx_l1d_flush_mutex = internal global %struct.mutex { %struct.list_head { %struct.list_head* bitcast (i8* getelementptr (i8, i8* bitcast (%struct.mutex* @vmx_l1d_flush_mutex to i8*), i64 16) to %struct.list_head*), %struct.list_head* bitcast (i8* getelementptr (i8, i8* bitcast (%struct.mutex* @vmx_l1d_flush_mutex to i8*), i64 16) to %struct.list_head*) } }, align 8
 
 define internal i32 @qux() {
   call void undef(%struct.mutex* @vmx_l1d_flush_mutex)
   ret i32 undef
 }
+
+; An initializer could use itself as part of the initialization.
+
+@kvm_debugfs_entries = internal global %struct.list_head { %struct.list_head* @kvm_debugfs_entries, %struct.list_head* @kvm_debugfs_entries }, align 8
+
+define i64 @mux() {
+  %1 = load i8*, i8** bitcast (%struct.list_head* @kvm_debugfs_entries to i8**), align 8
+  ret i64 undef
+}

llvm/tools/llvm-diff/DifferenceEngine.cpp

if (isa<ConstantStruct>(L)) {
       if (LTy->getNumElements() != RTy->getNumElements() ||
           LTy->isPacked() != RTy->isPacked())
         return false;
 
       for (unsigned I = 0; I < LTy->getNumElements(); I++) {
         const Value *LAgg = CSL->getAggregateElement(I);
         const Value *RAgg = CSR->getAggregateElement(I);
 
+        if (LAgg == SavedLHS || RAgg == SavedRHS) {
+          if (LAgg != SavedLHS || RAgg != SavedRHS)
+            // If the left and right operands aren't both re-analyzing the
+            // variable, then the initialiers don't match, so report "false".
+            // Otherwise, we skip these operands..
+            return false;
+
+          continue;
+        }
+
         if (!equivalentAsOperands(LAgg, RAgg)) {
           return false;
         }
       }
 
       return true;
     }