[llvm-diff] Explicitly check ConstantArrays

Global initializers may be ConstantArrays. They need to be checked
explicitly, because different-yet-still-equivalent type names may be
used for each, and/or a GEP instruction may appear in one.

Author: isanbard

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

@@ -0,0 +1,12 @@
+; RUN: llvm-diff %s %s
+
+; An initializer that has a GEP instruction in it won't match itself in
+; llvm-diff unless the a deep comparison is done on the initializer.
+
+@gv1 = external dso_local global [28 x i16], align 16
+@gv2 = private unnamed_addr constant [2 x i16*] [i16* getelementptr inbounds ([28 x i16], [28 x i16]* @gv1, i32 0, i32 0), i16* poison], align 16
+
+define void @foo() {
+  %1 = getelementptr [2 x i16*], [2 x i16*]* @gv2, i64 0, i64 undef
+  ret void
+}

llvm/tools/llvm-diff/DifferenceEngine.cpp

@@ -404,6 +404,7 @@ class FunctionDifferenceEngine {
     return false;
   }
 
+public:
   bool equivalentAsOperands(const Constant *L, const Constant *R) {
     // Use equality as a preliminary filter.
     if (L == R)
@@ -446,6 +447,24 @@ class FunctionDifferenceEngine {
       return true;
     }
 
+    // If L and R are ConstantArrays, compare the element count and types.
+    if (isa<ConstantArray>(L)) {
+      const ConstantArray *CAL = cast<ConstantArray>(L);
+      const ConstantArray *CAR = cast<ConstantArray>(R);
+      // Sometimes a type may be equivalent, but not uniquified---e.g. it may
+      // contain a GEP instruction. Do a deeper comparison of the types.
+      if (CAL->getType()->getNumElements() != CAR->getType()->getNumElements())
+        return false;
+
+      for (unsigned I = 0; I < CAL->getType()->getNumElements(); ++I) {
+        if (!equivalentAsOperands(CAL->getAggregateElement(I),
+                                  CAR->getAggregateElement(I)))
+          return false;
+      }
+
+      return true;
+    }
+
     return false;
   }
 
@@ -766,7 +785,8 @@ bool DifferenceEngine::equivalentAsOperands(const GlobalValue *L,
     const GlobalVariable *GVR = cast<GlobalVariable>(R);
     if (GVL->hasLocalLinkage() && GVL->hasUniqueInitializer() &&
         GVR->hasLocalLinkage() && GVR->hasUniqueInitializer())
-      return GVL->getInitializer() == GVR->getInitializer();
+      return FunctionDifferenceEngine(*this).equivalentAsOperands(
+          GVL->getInitializer(), GVR->getInitializer());
   }
 
   return L->getName() == R->getName();