diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -1996,11 +1996,6 @@
     }
   } else if (auto *C1VTy = dyn_cast<VectorType>(C1->getType())) {
 
-    // Do not iterate on scalable vector. The number of elements is unknown at
-    // compile-time.
-    if (isa<ScalableVectorType>(C1VTy))
-      return nullptr;
-
     // Fast path for splatted constants.
     if (Constant *C1Splat = C1->getSplatValue())
       if (Constant *C2Splat = C2->getSplatValue())
@@ -2008,6 +2003,11 @@
             C1VTy->getElementCount(),
             ConstantExpr::getCompare(pred, C1Splat, C2Splat));
 
+    // Do not iterate on scalable vector. The number of elements is unknown at
+    // compile-time.
+    if (isa<ScalableVectorType>(C1VTy))
+      return nullptr;
+
     // If we can constant fold the comparison of each element, constant fold
     // the whole vector comparison.
     SmallVector<Constant*, 4> ResElts;
diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -1501,6 +1501,8 @@
     return CV->getSplatValue();
   if (const ConstantVector *CV = dyn_cast<ConstantVector>(this))
     return CV->getSplatValue(AllowUndefs);
+  // FIXME: this should be able to get a splat value from scalable vector splats
+  // of the form returned by ConstantVector::getSplat()
   return nullptr;
 }
 
diff --git a/llvm/test/Analysis/ConstantFolding/cmp-vec-fast-path.ll b/llvm/test/Analysis/ConstantFolding/cmp-vec-fast-path.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Analysis/ConstantFolding/cmp-vec-fast-path.ll
@@ -0,0 +1,424 @@
+
+; Check that cmp's of scalable vector splats are constant folded
+; FIXME: Constant::getSplatValue() only knows how to get the splat value of
+;        ConstantAggregateZero values with scalable vector type. Once it is
+;        extended to support arbitrary splats, this test should be updated
+
+; RUN: opt -instcombine -S < %s | FileCheck %s
+
+
+; CHECK-LABEL: i32cmp_eq_fixed
+; CHECK: ret <2 x i1> shufflevector (<vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0), <vscale x 2 x i1> undef, <vscale x 2 x i32> zeroinitializer)
+define <2 x i1> @i32cmp_eq_fixed() {
+  %res = icmp eq <2 x i32> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_eq_scalable
+; CHECK: ret <vscale x 2 x i1> <i1 true, i1 true>
+define <vscale x 2 x i1> @i32cmp_eq_scalable() {
+  %res = icmp eq <vscale x 2 x i32> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_ne_fixed
+; CHECK: ret <2 x i1> zeroinitializer
+define <2 x i1> @i32cmp_ne_fixed() {
+  %res = icmp ne <2 x i32> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_ne_scalable
+; CHECK: ret <vscale x 2 x i1> zeroinitializer
+define <vscale x 2 x i1> @i32cmp_ne_scalable() {
+  %res = icmp ne <vscale x 2 x i32> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_ugt_fixed
+; CHECK: ret <2 x i1> zeroinitializer
+define <2 x i1> @i32cmp_ugt_fixed() {
+  %res = icmp ugt <2 x i32> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_ugt_scalable
+; CHECK: ret <vscale x 2 x i1> zeroinitializer
+define <vscale x 2 x i1> @i32cmp_ugt_scalable() {
+  %res = icmp ugt <vscale x 2 x i32> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_uge_fixed
+; CHECK: ret <2 x i1> shufflevector (<vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0), <vscale x 2 x i1> undef, <vscale x 2 x i32> zeroinitializer)
+define <2 x i1> @i32cmp_uge_fixed() {
+  %res = icmp uge <2 x i32> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_uge_scalable
+; CHECK: ret <vscale x 2 x i1> <i1 true, i1 true>
+define <vscale x 2 x i1> @i32cmp_uge_scalable() {
+  %res = icmp uge <vscale x 2 x i32> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_ult_fixed
+; CHECK: ret <2 x i1> zeroinitializer
+define <2 x i1> @i32cmp_ult_fixed() {
+  %res = icmp ult <2 x i32> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_ult_scalable
+; CHECK: ret <vscale x 2 x i1> zeroinitializer
+define <vscale x 2 x i1> @i32cmp_ult_scalable() {
+  %res = icmp ult <vscale x 2 x i32> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_ule_fixed
+; CHECK: ret <2 x i1> shufflevector (<vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0), <vscale x 2 x i1> undef, <vscale x 2 x i32> zeroinitializer)
+define <2 x i1> @i32cmp_ule_fixed() {
+  %res = icmp ule <2 x i32> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_ule_scalable
+; CHECK: ret <vscale x 2 x i1> <i1 true, i1 true>
+define <vscale x 2 x i1> @i32cmp_ule_scalable() {
+  %res = icmp ule <vscale x 2 x i32> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_sgt_fixed
+; CHECK: ret <2 x i1> zeroinitializer
+define <2 x i1> @i32cmp_sgt_fixed() {
+  %res = icmp sgt <2 x i32> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_sgt_scalable
+; CHECK: ret <vscale x 2 x i1> zeroinitializer
+define <vscale x 2 x i1> @i32cmp_sgt_scalable() {
+  %res = icmp sgt <vscale x 2 x i32> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_sge_fixed
+; CHECK: ret <2 x i1> shufflevector (<vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0), <vscale x 2 x i1> undef, <vscale x 2 x i32> zeroinitializer)
+define <2 x i1> @i32cmp_sge_fixed() {
+  %res = icmp sge <2 x i32> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_sge_scalable
+; CHECK: ret <vscale x 2 x i1> <i1 true, i1 true>
+define <vscale x 2 x i1> @i32cmp_sge_scalable() {
+  %res = icmp sge <vscale x 2 x i32> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_slt_fixed
+; CHECK: ret <2 x i1> zeroinitializer
+define <2 x i1> @i32cmp_slt_fixed() {
+  %res = icmp slt <2 x i32> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_slt_scalable
+; CHECK: ret <vscale x 2 x i1> zeroinitializer
+define <vscale x 2 x i1> @i32cmp_slt_scalable() {
+  %res = icmp slt <vscale x 2 x i32> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_sle_fixed
+; CHECK: ret <2 x i1> shufflevector (<vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0), <vscale x 2 x i1> undef, <vscale x 2 x i32> zeroinitializer)
+define <2 x i1> @i32cmp_sle_fixed() {
+  %res = icmp sle <2 x i32> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: i32cmp_sle_scalable
+; CHECK: ret <vscale x 2 x i1> <i1 true, i1 true>
+define <vscale x 2 x i1> @i32cmp_sle_scalable() {
+  %res = icmp sle <vscale x 2 x i32> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_false_fixed
+; CHECK: ret <2 x i1> zeroinitializer
+define <2 x i1> @floatcmp_false_fixed() {
+  %res = fcmp false <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_false_scalable
+; CHECK: ret <vscale x 2 x i1> zeroinitializer
+define <vscale x 2 x i1> @floatcmp_false_scalable() {
+  %res = fcmp false <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_oeq_fixed
+; CHECK: ret <2 x i1> shufflevector (<vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0), <vscale x 2 x i1> undef, <vscale x 2 x i32> zeroinitializer)
+define <2 x i1> @floatcmp_oeq_fixed() {
+  %res = fcmp oeq <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_oeq_scalable
+; CHECK: ret <vscale x 2 x i1> <i1 true, i1 true>
+define <vscale x 2 x i1> @floatcmp_oeq_scalable() {
+  %res = fcmp oeq <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_ogt_fixed
+; CHECK: ret <2 x i1> zeroinitializer
+define <2 x i1> @floatcmp_ogt_fixed() {
+  %res = fcmp ogt <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_ogt_scalable
+; CHECK: ret <vscale x 2 x i1> zeroinitializer
+define <vscale x 2 x i1> @floatcmp_ogt_scalable() {
+  %res = fcmp ogt <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_oge_fixed
+; CHECK: ret <2 x i1> shufflevector (<vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0), <vscale x 2 x i1> undef, <vscale x 2 x i32> zeroinitializer)
+define <2 x i1> @floatcmp_oge_fixed() {
+  %res = fcmp oge <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_oge_scalable
+; CHECK: ret <vscale x 2 x i1> <i1 true, i1 true>
+define <vscale x 2 x i1> @floatcmp_oge_scalable() {
+  %res = fcmp oge <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_olt_fixed
+; CHECK: ret <2 x i1> zeroinitializer
+define <2 x i1> @floatcmp_olt_fixed() {
+  %res = fcmp olt <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_olt_scalable
+; CHECK: ret <vscale x 2 x i1> zeroinitializer
+define <vscale x 2 x i1> @floatcmp_olt_scalable() {
+  %res = fcmp olt <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_ole_fixed
+; CHECK: ret <2 x i1> shufflevector (<vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0), <vscale x 2 x i1> undef, <vscale x 2 x i32> zeroinitializer)
+define <2 x i1> @floatcmp_ole_fixed() {
+  %res = fcmp ole <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_ole_scalable
+; CHECK: ret <vscale x 2 x i1> <i1 true, i1 true>
+define <vscale x 2 x i1> @floatcmp_ole_scalable() {
+  %res = fcmp ole <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_one_fixed
+; CHECK: ret <2 x i1> zeroinitializer
+define <2 x i1> @floatcmp_one_fixed() {
+  %res = fcmp one <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_one_scalable
+; CHECK: ret <vscale x 2 x i1> zeroinitializer
+define <vscale x 2 x i1> @floatcmp_one_scalable() {
+  %res = fcmp one <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_ord_fixed
+; CHECK: ret <2 x i1> shufflevector (<vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0), <vscale x 2 x i1> undef, <vscale x 2 x i32> zeroinitializer)
+define <2 x i1> @floatcmp_ord_fixed() {
+  %res = fcmp ord <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_ord_scalable
+; CHECK: ret <vscale x 2 x i1> <i1 true, i1 true>
+define <vscale x 2 x i1> @floatcmp_ord_scalable() {
+  %res = fcmp ord <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_ueq_fixed
+; CHECK: ret <2 x i1> shufflevector (<vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0), <vscale x 2 x i1> undef, <vscale x 2 x i32> zeroinitializer)
+define <2 x i1> @floatcmp_ueq_fixed() {
+  %res = fcmp ueq <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_ueq_scalable
+; CHECK: ret <vscale x 2 x i1> <i1 true, i1 true>
+define <vscale x 2 x i1> @floatcmp_ueq_scalable() {
+  %res = fcmp ueq <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_ugt_fixed
+; CHECK: ret <2 x i1> zeroinitializer
+define <2 x i1> @floatcmp_ugt_fixed() {
+  %res = fcmp ugt <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_ugt_scalable
+; CHECK: ret <vscale x 2 x i1> zeroinitializer
+define <vscale x 2 x i1> @floatcmp_ugt_scalable() {
+  %res = fcmp ugt <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_uge_fixed
+; CHECK: ret <2 x i1> shufflevector (<vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0), <vscale x 2 x i1> undef, <vscale x 2 x i32> zeroinitializer)
+define <2 x i1> @floatcmp_uge_fixed() {
+  %res = fcmp uge <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_uge_scalable
+; CHECK: ret <vscale x 2 x i1> <i1 true, i1 true>
+define <vscale x 2 x i1> @floatcmp_uge_scalable() {
+  %res = fcmp uge <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_ult_fixed
+; CHECK: ret <2 x i1> zeroinitializer
+define <2 x i1> @floatcmp_ult_fixed() {
+  %res = fcmp ult <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_ult_scalable
+; CHECK: ret <vscale x 2 x i1> zeroinitializer
+define <vscale x 2 x i1> @floatcmp_ult_scalable() {
+  %res = fcmp ult <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_ule_fixed
+; CHECK: ret <2 x i1> shufflevector (<vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0), <vscale x 2 x i1> undef, <vscale x 2 x i32> zeroinitializer)
+define <2 x i1> @floatcmp_ule_fixed() {
+  %res = fcmp ule <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_ule_scalable
+; CHECK: ret <vscale x 2 x i1> <i1 true, i1 true>
+define <vscale x 2 x i1> @floatcmp_ule_scalable() {
+  %res = fcmp ule <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_une_fixed
+; CHECK: ret <2 x i1> zeroinitializer
+define <2 x i1> @floatcmp_une_fixed() {
+  %res = fcmp une <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_une_scalable
+; CHECK: ret <vscale x 2 x i1> zeroinitializer
+define <vscale x 2 x i1> @floatcmp_une_scalable() {
+  %res = fcmp une <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_uno_fixed
+; CHECK: ret <2 x i1> zeroinitializer
+define <2 x i1> @floatcmp_uno_fixed() {
+  %res = fcmp uno <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_uno_scalable
+; CHECK: ret <vscale x 2 x i1> zeroinitializer
+define <vscale x 2 x i1> @floatcmp_uno_scalable() {
+  %res = fcmp uno <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_true_fixed
+; CHECK: ret <2 x i1> shufflevector (<vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0), <vscale x 2 x i1> undef, <vscale x 2 x i32> zeroinitializer)
+define <2 x i1> @floatcmp_true_fixed() {
+  %res = fcmp true <2 x float> zeroinitializer, zeroinitializer
+  ret <2 x i1> %res
+}
+
+
+; CHECK-LABEL: floatcmp_true_scalable
+; CHECK: ret <vscale x 2 x i1> <i1 true, i1 true>
+define <vscale x 2 x i1> @floatcmp_true_scalable() {
+  %res = fcmp true <vscale x 2 x float> zeroinitializer, zeroinitializer
+  ret <vscale x 2 x i1> %res
+}
+