diff --git a/OVERVIEW.txt b/OVERVIEW.txt
index a0768923e2..4b88d052a0 100644
--- a/OVERVIEW.txt
+++ b/OVERVIEW.txt
@@ -94,8 +94,6 @@ sources
     jam                 - Jam script interpreter.
     parser-run-time     - Support for parsers.
     source-records      - Reads source files and tracks location.
-    stack-walker        - Debugging on UNIX by walking the stack. Nowadays
-                          directly in the run-time.
     walker              - Build has-a tree.
   project-manager       - Takes care about dependencies of projects and actual
                           invocation of linker, etc.
diff --git a/documentation/source/release-notes/2024.2.rst b/documentation/source/release-notes/2024.2.rst
index 06ab1a171a..22daa6abb2 100644
--- a/documentation/source/release-notes/2024.2.rst
+++ b/documentation/source/release-notes/2024.2.rst
@@ -26,6 +26,19 @@ Compiler
 * The build rules for unified executables now properly depend on
   copying included run-time libraries such as libunwind.
 
+* Optimizations that allow the type of ``if`` expressions to be more
+  accurately estimated have been improved. For example, in this
+  function:
+
+  .. code-block::
+
+    define function if-example (arg :: false-or(<integer>)) => (result :: <integer>);
+      min(arg | 20, 30)
+    end;
+
+  the comparison can now be properly inlined because the first
+  argument to :drm:`min` is known to be an :drm:`<integer>`.
+
 Tools
 =====
 
@@ -61,6 +74,11 @@ System
   :const:`$machine-architecture`.  The old name will remain, for backward
   compatibility.
 
+Other
+-----
+
+* The obsolete (32-bit x86-only) ``stack-walker`` library was removed.
+
 Contributors
 ============
 
diff --git a/sources/dfmc/optimization/assignment.dylan b/sources/dfmc/optimization/assignment.dylan
index 254833bffb..af2b44503d 100644
--- a/sources/dfmc/optimization/assignment.dylan
+++ b/sources/dfmc/optimization/assignment.dylan
@@ -190,14 +190,20 @@ define method maybe-rename-temporaries-in-conditional
           (c.environment, <constrain-type>,
            value: to-be-renamed, type: constraint);
       let then-f = c.consequent;
+      let merge-c :: <if-merge> = c.next-computation;
       let changed? = #f;
       rename-temporary!(to-be-renamed, tt-t);
-      for-computations(tc from then-f before c.next-computation)
+      for-computations(tc from then-f before merge-c)
         let now-changed? = rename-temporary-references!(tc, to-be-renamed, tt-t);
         changed? := (changed? | now-changed?);
       end;
+      // The left side of the merge is also part of the consequent
+      if (merge-c.merge-left-value == to-be-renamed)
+        merge-replace-left-value!(merge-c, to-be-renamed, tt-t);
+        changed? := #t;
+      end;
       if (changed?)
-        insert-computation-before!(then-f, tt-c);
+        insert-computation-before-reference!(then-f, tt-c, tt-t);
       else // It's not used in the consequent, so get rid of it.
         remove-user!(to-be-renamed, tt-c);
       end;
diff --git a/sources/dfmc/optimization/calls.dylan b/sources/dfmc/optimization/calls.dylan
index 3ad03bfd22..9f53b3910d 100644
--- a/sources/dfmc/optimization/calls.dylan
+++ b/sources/dfmc/optimization/calls.dylan
@@ -79,13 +79,19 @@ define method do-optimize-instance?-user(c :: <if>, object, type) => ();
     = make-with-temporary(c.environment, <constrain-type>,
                           value: object, type: type);
   let then-f = c.consequent;
+  let merge-c :: <if-merge> = c.next-computation;
   let changed? = #f;
-  for-computations(tc from then-f before c.next-computation)
+  for-computations(tc from then-f before merge-c)
     let now-changed? = rename-temporary-references!(tc, object, tt-t);
     changed? := (changed? | now-changed?);
   end;
+  // The left side of the merge is also part of the consequent
+  if (merge-c.merge-left-value == object)
+    merge-replace-left-value!(merge-c, object, tt-t);
+    changed? := #t;
+  end;
   if (changed?)
-    insert-computation-before!(then-f, tt-c);
+    insert-computation-before-reference!(then-f, tt-c, tt-t);
   else // It's not used in the consequent, so get rid of it.
     remove-user!(object, tt-c);
   end
diff --git a/sources/environment/dswank/library.dylan b/sources/environment/dswank/library.dylan
index 20f5e8fcb7..73664829f8 100644
--- a/sources/environment/dswank/library.dylan
+++ b/sources/environment/dswank/library.dylan
@@ -19,7 +19,6 @@ define library dswank
   use file-source-records;
   use system;
   use registry-projects;
-  //use stack-walker;
   use release-info;
   use dfmc-back-end-implementations;
 end library;
@@ -46,7 +45,6 @@ define module dswank
   use file-system;
   use locators;
   use registry-projects;
-  //use stack-walker;
   use release-info;
   use operating-system;
 end module;
diff --git a/sources/lib/stack-walker/getebp.c b/sources/lib/stack-walker/getebp.c
deleted file mode 100644
index 4d263d7fa6..0000000000
--- a/sources/lib/stack-walker/getebp.c
+++ /dev/null
@@ -1,35 +0,0 @@
-#include <stdio.h>
-#define __USE_GNU
-#include <dlfcn.h>
-
-int getebp () {
-    int ebp;
-    asm("mov (%%ebp), %0"
-        :"=r"(ebp));
-    return ebp;
-};
-
-void walkstack() {
-  int ebp = getebp();
-  int eip;
-  int rc;
-  Dl_info info;
-
-  while(ebp) {
-    eip = *((int*)ebp + 1);
-    rc = dladdr((void*)eip, &info);
-    if (!rc||(!info.dli_sname && !info.dli_fname)) {
-      printf("0x%x (unknown)\n");
-    } else {
-      if (!info.dli_sname) {
-        printf("0x%x (%s)\n", eip, info.dli_fname);
-      } else {
-        printf("%s+%i (%s)\n",
-               info.dli_sname,
-	       eip - (int)info.dli_saddr,
-	       info.dli_fname);
-      }
-    }
-    ebp = *((int*)ebp);
-  }
-}
diff --git a/sources/lib/stack-walker/library.dylan b/sources/lib/stack-walker/library.dylan
deleted file mode 100644
index ca3b616a4f..0000000000
--- a/sources/lib/stack-walker/library.dylan
+++ /dev/null
@@ -1,19 +0,0 @@
-module:    dylan-user
-copyright: Original Code is Copyright (c) 2007 Dylan Hackers;
-           All rights reversed.
-License:   See License.txt in this distribution for details.
-Warranty:  Distributed WITHOUT WARRANTY OF ANY KIND
-
-define library stack-walker
-  use common-dylan;
-  use c-ffi;
-
-  export stack-walker;
-end;
-
-define module stack-walker
-  use common-dylan;
-  use c-ffi;
-
-  export walk-stack;
-end;
diff --git a/sources/lib/stack-walker/stack-walker.dylan b/sources/lib/stack-walker/stack-walker.dylan
deleted file mode 100644
index afcf18b9ef..0000000000
--- a/sources/lib/stack-walker/stack-walker.dylan
+++ /dev/null
@@ -1,9 +0,0 @@
-module:    stack-walker
-copyright: Original Code is Copyright (c) 2007 Dylan Hackers;
-           All rights reversed.
-License:   See License.txt in this distribution for details.
-Warranty:  Distributed WITHOUT WARRANTY OF ANY KIND
-
-define C-function walk-stack
-  c-name: "walkstack"
-end;
diff --git a/sources/lib/stack-walker/stack-walker.lid b/sources/lib/stack-walker/stack-walker.lid
deleted file mode 100644
index 73c189ec52..0000000000
--- a/sources/lib/stack-walker/stack-walker.lid
+++ /dev/null
@@ -1,9 +0,0 @@
-library: stack-walker
-c-source-files: getebp.c
-files: library
-       stack-walker
-Platforms: arm-linux
-           x86-freebsd
-           x86-linux
-           x86-netbsd
-           x86_64-linux
diff --git a/sources/registry/aarch64-linux/stack-walker b/sources/registry/aarch64-linux/stack-walker
deleted file mode 100644
index 262021218e..0000000000
--- a/sources/registry/aarch64-linux/stack-walker
+++ /dev/null
@@ -1 +0,0 @@
-abstract://dylan/lib/stack-walker/stack-walker.lid
diff --git a/sources/registry/arm-linux/stack-walker b/sources/registry/arm-linux/stack-walker
deleted file mode 100644
index 262021218e..0000000000
--- a/sources/registry/arm-linux/stack-walker
+++ /dev/null
@@ -1 +0,0 @@
-abstract://dylan/lib/stack-walker/stack-walker.lid
diff --git a/sources/registry/riscv64-linux/stack-walker b/sources/registry/riscv64-linux/stack-walker
deleted file mode 100644
index 262021218e..0000000000
--- a/sources/registry/riscv64-linux/stack-walker
+++ /dev/null
@@ -1 +0,0 @@
-abstract://dylan/lib/stack-walker/stack-walker.lid
diff --git a/sources/registry/x86-freebsd/stack-walker b/sources/registry/x86-freebsd/stack-walker
deleted file mode 100644
index 262021218e..0000000000
--- a/sources/registry/x86-freebsd/stack-walker
+++ /dev/null
@@ -1 +0,0 @@
-abstract://dylan/lib/stack-walker/stack-walker.lid
diff --git a/sources/registry/x86-linux/stack-walker b/sources/registry/x86-linux/stack-walker
deleted file mode 100644
index 262021218e..0000000000
--- a/sources/registry/x86-linux/stack-walker
+++ /dev/null
@@ -1 +0,0 @@
-abstract://dylan/lib/stack-walker/stack-walker.lid
diff --git a/sources/registry/x86-netbsd/stack-walker b/sources/registry/x86-netbsd/stack-walker
deleted file mode 100644
index 262021218e..0000000000
--- a/sources/registry/x86-netbsd/stack-walker
+++ /dev/null
@@ -1 +0,0 @@
-abstract://dylan/lib/stack-walker/stack-walker.lid
diff --git a/sources/registry/x86_64-linux/stack-walker b/sources/registry/x86_64-linux/stack-walker
deleted file mode 100644
index 262021218e..0000000000
--- a/sources/registry/x86_64-linux/stack-walker
+++ /dev/null
@@ -1 +0,0 @@
-abstract://dylan/lib/stack-walker/stack-walker.lid