interp: add regression test for partial store aliasing

Adds a third init function to the store testdata: an initial partial
store puts the buffer into the current memory view, then a partial load
is followed by another partial store at the same offset, and finally the
loaded value is written to a separate global.

The expected output captures the current (incorrect) behavior of the
in-place partial store optimization: the loaded value gets corrupted by
the subsequent in-place store. The next commit fixes this.

Author: jakebailey

interp/testdata/store.ll

@@ -4,11 +4,14 @@ target triple = "x86_64--linux"
 @overlap.buf = global [4 x i8] c"\01\02\03\04"
 @alias.src = global [4 x i8] c"\05\06\07\08"
 @alias.dst = global [2 x i8] zeroinitializer
+@reload.buf = global [4 x i8] c"\01\02\03\04"
+@reload.out = global [2 x i8] zeroinitializer
 
 define void @runtime.initAll() unnamed_addr {
 entry:
   call void @overlap.init(ptr undef)
   call void @alias.init(ptr undef)
+  call void @reload.init(ptr undef)
   ret void
 }
 
@@ -30,3 +33,17 @@ entry:
   store i8 9, ptr @alias.dst
   ret void
 }
+
+define internal void @reload.init(ptr %context) unnamed_addr {
+entry:
+  ; First store makes reload.buf writable in the current memory view.
+  %tail = getelementptr [4 x i8], ptr @reload.buf, i32 0, i32 3
+  store i8 9, ptr %tail
+  ; Partial load whose result may share the underlying buffer.
+  %val = load i16, ptr @reload.buf
+  ; Subsequent in-place partial store; this must not corrupt %val.
+  store i8 99, ptr @reload.buf
+  ; Write the originally-loaded value to a separate global.
+  store i16 %val, ptr @reload.out
+  ret void
+}

interp/testdata/store.out.ll

@@ -4,6 +4,8 @@ target triple = "x86_64--linux"
 @overlap.buf = local_unnamed_addr global [4 x i8] c"\01\01\02\09"
 @alias.src = local_unnamed_addr global [4 x i8] c"\05\06\07\08"
 @alias.dst = local_unnamed_addr global [2 x i8] c"\09\07"
+@reload.buf = local_unnamed_addr global [4 x i8] c"c\02\03\09"
+@reload.out = local_unnamed_addr global [2 x i8] c"c\02"
 
 define void @runtime.initAll() unnamed_addr {
 entry: