Emit getelementptr nuw for SliceExp for static array with const lower

bound

Author: kubo39

gen/toir.cpp

@@ -1293,8 +1293,16 @@ class ToElemVisitor : public Visitor {
       }
 
       // offset by lower
-      eptr = DtoGEP1(DtoMemType(etype->nextOf()), getBasePointer(), vlo, "lowerbound");
-
+#if LDC_LLVM_VER >= 2000
+      llvm::GEPNoWrapFlags nw = llvm::GEPNoWrapFlags::inBounds();
+      if (!needCheckUpper && !needCheckLower)
+        nw |= llvm::GEPNoWrapFlags::noUnsignedWrap();
+#endif
+      eptr = DtoGEP1(DtoMemType(etype->nextOf()), getBasePointer(), vlo, "lowerbound"
+#if LDC_LLVM_VER >= 2000
+                   , nullptr, nw
+#endif
+      );
       // adjust length
       elen = p->ir->CreateSub(vup, vlo);
     }

tests/codegen/inbounds.d

@@ -79,7 +79,7 @@ int foo10(int[] a, int i) {
 // SliceExp for static array with const lower bound
 // CHECK-LABEL: @foo11
 int[] foo11(ref int[3] a) {
-    // CHECK: getelementptr inbounds i32, ptr
+    // CHECK: getelementptr inbounds{{( nuw)?}} i32, ptr
     return a[1 .. $];
 }