diff --git a/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td b/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
--- a/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
+++ b/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
@@ -392,7 +392,7 @@
   let assemblyFormat = "$inputs attr-dict";
 }
 
-def Shape_AssumingAllOp : Shape_Op<"assuming_all", [NoSideEffect]> {
+def Shape_AssumingAllOp : Shape_Op<"assuming_all", [Commutative, NoSideEffect]> {
   let summary = "Return a logical AND of all witnesses.";
   let description = [{
     Used to simplify constraints as any single failing precondition is enough
@@ -417,6 +417,8 @@
   let results = (outs Shape_WitnessType:$result);
 
   let assemblyFormat = "$inputs attr-dict";
+
+  let hasCanonicalizer = 1;
 }
 
 def Shape_AssumingOp : Shape_Op<"assuming",
diff --git a/mlir/lib/Dialect/Shape/CMakeLists.txt b/mlir/lib/Dialect/Shape/CMakeLists.txt
--- a/mlir/lib/Dialect/Shape/CMakeLists.txt
+++ b/mlir/lib/Dialect/Shape/CMakeLists.txt
@@ -1,3 +1,7 @@
+set(LLVM_TARGET_DEFINITIONS IR/ShapeCanonicalization.td)
+mlir_tablegen(IR/ShapeCanonicalization.inc -gen-rewriters)
+add_public_tablegen_target(MLIRShapeCanonicalizationIncGen)
+
 add_mlir_dialect_library(MLIRShape
   IR/Shape.cpp
 
diff --git a/mlir/lib/Dialect/Shape/IR/Shape.cpp b/mlir/lib/Dialect/Shape/IR/Shape.cpp
--- a/mlir/lib/Dialect/Shape/IR/Shape.cpp
+++ b/mlir/lib/Dialect/Shape/IR/Shape.cpp
@@ -18,6 +18,9 @@
 using namespace mlir;
 using namespace mlir::shape;
 
+namespace {
+#include "IR/ShapeCanonicalization.inc"
+}
 ShapeDialect::ShapeDialect(MLIRContext *context)
     : Dialect(getDialectNamespace(), context) {
   addOperations<
@@ -151,6 +154,15 @@
   p.printOptionalAttrDict(op.getAttrs());
 }
 
+//===----------------------------------------------------------------------===//
+// AssumingAllOp
+//===----------------------------------------------------------------------===//
+void AssumingAllOp::getCanonicalizationPatterns(
+    OwningRewritePatternList &patterns, MLIRContext *context) {
+  // If all true, replace with true. Folding?
+  patterns.insert<ConstantAssumingAll>(context);
+}
+
 //===----------------------------------------------------------------------===//
 // BroadcastOp
 //===----------------------------------------------------------------------===//
diff --git a/mlir/lib/Dialect/Shape/IR/ShapeCanonicalization.td b/mlir/lib/Dialect/Shape/IR/ShapeCanonicalization.td
new file mode 100644
--- /dev/null
+++ b/mlir/lib/Dialect/Shape/IR/ShapeCanonicalization.td
@@ -0,0 +1,13 @@
+include "mlir/Dialect/Shape/IR/ShapeOps.td"
+
+// Constraints
+def AllInputsTrueWitnesses : Constraint<CPred<[{
+        llvm::all_of($0.getOwner()->getOperands(), [](mlir::Value op) {
+          return op.getDefiningOp<mlir::shape::TrueWitnessOp>();
+        })
+      }]>>;
+
+// Canonicalization patterns.
+def ConstantAssumingAll : Pat<(Shape_AssumingAllOp:$op $input),
+          (Shape_TrueWitnessOp),
+          [(AllInputsTrueWitnesses $op)] >;
diff --git a/mlir/test/Dialect/Shape/canonicalize.mlir b/mlir/test/Dialect/Shape/canonicalize.mlir
--- a/mlir/test/Dialect/Shape/canonicalize.mlir
+++ b/mlir/test/Dialect/Shape/canonicalize.mlir
@@ -1,4 +1,4 @@
-// RUN: mlir-opt -split-input-file -canonicalize <%s | FileCheck %s --dump-input=fail
+// RUN: mlir-opt -split-input-file -allow-unregistered-dialect -canonicalize <%s | FileCheck %s --dump-input=fail
 
 // -----
 // CHECK-LABEL: func @f
@@ -106,3 +106,34 @@
   %ret = shape.from_extents %e0, %arg0
   return %ret : !shape.shape
 }
+
+// -----
+// assuming_all with known true witnesses can be folded
+// CHECK-LABEL: func @f
+func @f() {
+  // CHECK-NEXT: shape.true_witness
+  // CHECK-NEXT: consume.witness
+  // CHECK-NEXT: return
+  %0 = shape.true_witness
+  %1 = shape.true_witness
+  %2 = shape.true_witness
+  %3 = shape.assuming_all %0, %1, %2
+  "consume.witness"(%3) : (!shape.witness) -> ()
+  return
+}
+
+// -----
+// assuming_all should not be removed if not all witnesses are statically true.
+// CHECK-LABEL: func @f
+func @f() {
+  // CHECK-NEXT: %[[TRUE:.*]] = shape.true_witness
+  // CHECK-NEXT: %[[UNKNOWN:.*]] = "test.source"
+  // CHECK-NEXT: shape.assuming_all %[[TRUE]], %[[UNKNOWN]]
+  // CHECK-NEXT: consume.witness
+  // CHECK-NEXT: return
+  %0 = shape.true_witness
+  %1 = "test.source"() : () -> !shape.witness
+  %2 = shape.assuming_all %0, %1
+  "consume.witness"(%2) : (!shape.witness) -> ()
+  return
+}