From db80cae8336aa43fd9ac72e2566a49c265b426fc Mon Sep 17 00:00:00 2001
From: Alon Zakai <azakai@google.com>
Date: Fri, 21 Aug 2026 16:35:02 -0700
Subject: [PATCH] fix

---
 src/passes/ConstraintAnalysis.cpp             |  8 ++-
 .../lit/passes/constraint-analysis-loops.wast | 53 +++++++++++++++++++
 2 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/src/passes/ConstraintAnalysis.cpp b/src/passes/ConstraintAnalysis.cpp
index 324e2ef0312..a3bfbb11808 100644
--- a/src/passes/ConstraintAnalysis.cpp
+++ b/src/passes/ConstraintAnalysis.cpp
@@ -655,13 +655,17 @@ struct ConstraintAnalysis
     if (branch.constraint.op == Abstract::LtS ||
         branch.constraint.op == Abstract::LeS) {
       constraints.set(branch.local, branch.constraint);
-      constraints.approximateAnd(branch.local, {GeS, {*N}});
+      if (!constraints.unreachable) {
+        constraints.approximateAnd(branch.local, {GeS, {*N}});
+      }
       return true;
     }
     if (branch.constraint.op == Abstract::LtU ||
         branch.constraint.op == Abstract::LeU) {
       constraints.set(branch.local, branch.constraint);
-      constraints.approximateAnd(branch.local, {GeU, {*N}});
+      if (!constraints.unreachable) {
+        constraints.approximateAnd(branch.local, {GeU, {*N}});
+      }
       return true;
     }
 
diff --git a/test/lit/passes/constraint-analysis-loops.wast b/test/lit/passes/constraint-analysis-loops.wast
index a865c5b8651..8b6513d4dcd 100644
--- a/test/lit/passes/constraint-analysis-loops.wast
+++ b/test/lit/passes/constraint-analysis-loops.wast
@@ -1520,4 +1520,57 @@
       )
     )
   )
+
+  ;; CHECK:      (func $impossible-branch (type $0)
+  ;; CHECK-NEXT:  (local $x i32)
+  ;; CHECK-NEXT:  (local $y i32)
+  ;; CHECK-NEXT:  (loop $loop
+  ;; CHECK-NEXT:   (br_if $loop
+  ;; CHECK-NEXT:    (i32.lt_s
+  ;; CHECK-NEXT:     (local.get $x)
+  ;; CHECK-NEXT:     (local.get $y)
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $impossible-branch
+    (local $x i32)
+    (local $y i32)
+    (loop $loop
+      ;; x == y == 0, so x < y leads to a contradiction, and we never branch
+      ;; back up to the loop. We should not error here.
+      (br_if $loop
+        (i32.lt_s
+          (local.get $x)
+          (local.get $y)
+        )
+      )
+    )
+  )
+
+  ;; CHECK:      (func $impossible-branch-unsigned (type $0)
+  ;; CHECK-NEXT:  (local $x i32)
+  ;; CHECK-NEXT:  (local $y i32)
+  ;; CHECK-NEXT:  (loop $loop
+  ;; CHECK-NEXT:   (br_if $loop
+  ;; CHECK-NEXT:    (i32.lt_u
+  ;; CHECK-NEXT:     (local.get $x)
+  ;; CHECK-NEXT:     (local.get $y)
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $impossible-branch-unsigned
+    (local $x i32)
+    (local $y i32)
+    ;; As above, but unsigned.
+    (loop $loop
+      (br_if $loop
+        (i32.lt_u
+          (local.get $x)
+          (local.get $y)
+        )
+      )
+    )
+  )
 )