Index: lit/Expr/Inputs/ir-memory-map-basic.test
===================================================================
--- /dev/null
+++ lit/Expr/Inputs/ir-memory-map-basic.test
@@ -0,0 +1,25 @@
+malloc 0 1
+malloc 1 1
+
+malloc 2 1
+malloc 2 2
+malloc 2 4
+
+malloc 3 1
+malloc 3 2
+malloc 3 4
+
+malloc 128 1
+malloc 128 2
+malloc 128 4
+malloc 128 128
+
+malloc 2048 1
+malloc 2048 2
+malloc 2048 4
+
+malloc 3968 1
+malloc 3968 2
+malloc 3968 4
+
+malloc 0 1
Index: lit/Expr/Inputs/ir-memory-map-overlap1.test
===================================================================
--- /dev/null
+++ lit/Expr/Inputs/ir-memory-map-overlap1.test
@@ -0,0 +1,10 @@
+malloc 8 16
+malloc 16 8
+malloc 64 32
+malloc 1 8
+malloc 64 32
+malloc 64 8
+malloc 1024 32
+malloc 1 16
+malloc 8 16
+malloc 1024 16
\ No newline at end of file
Index: lit/Expr/TestIRMemoryMap.test
===================================================================
--- lit/Expr/TestIRMemoryMap.test
+++ lit/Expr/TestIRMemoryMap.test
@@ -1,28 +1,3 @@
 # RUN: %cxx %p/Inputs/call-function.cpp -g -o %t
-# RUN: lldb-test ir-memory-map %t %s
-
-malloc 0 1
-malloc 1 1
-
-malloc 2 1
-malloc 2 2
-malloc 2 4
-
-malloc 3 1
-malloc 3 2
-malloc 3 4
-
-malloc 128 1
-malloc 128 2
-malloc 128 4
-malloc 128 128
-
-malloc 2048 1
-malloc 2048 2
-malloc 2048 4
-
-malloc 3968 1
-malloc 3968 2
-malloc 3968 4
-
-malloc 0 1
+# RUN: lldb-test ir-memory-map %t %S/Inputs/ir-memory-map-basic.test
+# RUN: lldb-test ir-memory-map %t %S/Inputs/ir-memory-map-overlap1.test
Index: source/Expression/IRMemoryMap.cpp
===================================================================
--- source/Expression/IRMemoryMap.cpp
+++ source/Expression/IRMemoryMap.cpp
@@ -304,12 +304,25 @@
   size_t alignment_mask = alignment - 1;
   size_t allocation_size;
 
-  if (size == 0)
+  if (size == 0) {
+    // FIXME: Malloc(0) should either return an invalid address or assert, in
+    // order to cut down on unnecessary allocations.
     allocation_size = alignment;
-  else
-    allocation_size = (size & alignment_mask)
-                          ? ((size + alignment) & (~alignment_mask))
-                          : size;
+  } else {
+    // Round up the requested size to an aligned value, if needed.
+    if (size & alignment_mask)
+      allocation_size = ((size + alignment) & (~alignment_mask));
+    else
+      allocation_size = size;
+
+    // The process page cache does not see the requested alignment. We can't
+    // assume its result will be any more than 1-byte aligned. To work around
+    // this, request `alignment` additional bytes.
+    //
+    // FIXME: Pass the requested alignment into the process page cache to
+    // reduce internal fragmentation.
+    allocation_size += alignment;
+  }
 
   switch (policy) {
   default: