Index: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1337,6 +1337,12 @@
   if (!Sel1->hasOneUse())
     return nullptr;
 
+  // If the types do not match, look through any truncs to the underlying
+  // instruction.
+  if (Cmp00->getType() != X->getType())
+    if (auto *T = dyn_cast<TruncInst>(X))
+      X = T->getOperand(0);
+
   // We now can finish matching the condition of the outermost select:
   // it should either be the X itself, or an addition of some constant to X.
   Constant *C1;
@@ -1407,15 +1413,29 @@
   if (!match(Precond2, m_One()))
     return nullptr;
 
+  // If we are matching from a truncated input, we need to sext the
+  // ReplacementLow and ReplacementHigh values. Only do the transform if they
+  // are free to extend due to being constants.
+  if (X->getType() != Sel0.getType() &&
+      (!isa<Constant>(ReplacementLow) || !isa<Constant>(ReplacementHigh)))
+    return nullptr;
+
   // All good, finally emit the new pattern.
   Value *ShouldReplaceLow = Builder.CreateICmpSLT(X, ThresholdLowIncl);
   Value *ShouldReplaceHigh = Builder.CreateICmpSGE(X, ThresholdHighExcl);
-  Value *MaybeReplacedLow =
-      Builder.CreateSelect(ShouldReplaceLow, ReplacementLow, X);
-  Instruction *MaybeReplacedHigh =
-      SelectInst::Create(ShouldReplaceHigh, ReplacementHigh, MaybeReplacedLow);
-
-  return MaybeReplacedHigh;
+  Value *MaybeReplacedLow = Builder.CreateSelect(
+      ShouldReplaceLow, Builder.CreateSExt(ReplacementLow, X->getType()), X);
+
+  // Create the final select. If we looked through a truncate above, we will
+  // need to retruncate the result.
+  if (X->getType() == Sel0.getType())
+    return SelectInst::Create(ShouldReplaceHigh, ReplacementHigh,
+                              MaybeReplacedLow);
+
+  Value *MaybeReplacedHigh = Builder.CreateSelect(
+      ShouldReplaceHigh, Builder.CreateSExt(ReplacementHigh, X->getType()),
+      MaybeReplacedLow);
+  return new TruncInst(MaybeReplacedHigh, Sel0.getType());
 }
 
 // If we have
Index: llvm/test/Transforms/InstCombine/truncating-saturate.ll
===================================================================
--- llvm/test/Transforms/InstCombine/truncating-saturate.ll
+++ llvm/test/Transforms/InstCombine/truncating-saturate.ll
@@ -57,12 +57,11 @@
 
 define i16 @testi32i16i8(i32 %add) {
 ; CHECK-LABEL: @testi32i16i8(
-; CHECK-NEXT:    [[A:%.*]] = add i32 [[ADD:%.*]], 128
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 [[A]], 256
-; CHECK-NEXT:    [[T:%.*]] = trunc i32 [[ADD]] to i16
-; CHECK-NEXT:    [[C:%.*]] = icmp sgt i32 [[ADD]], -1
-; CHECK-NEXT:    [[F:%.*]] = select i1 [[C]], i16 127, i16 -128
-; CHECK-NEXT:    [[R:%.*]] = select i1 [[CMP]], i16 [[T]], i16 [[F]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp sgt i32 [[ADD:%.*]], -128
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i32 [[ADD]], i32 -128
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp slt i32 [[TMP2]], 127
+; CHECK-NEXT:    [[TMP4:%.*]] = select i1 [[TMP3]], i32 [[TMP2]], i32 127
+; CHECK-NEXT:    [[R:%.*]] = trunc i32 [[TMP4]] to i16
 ; CHECK-NEXT:    ret i16 [[R]]
 ;
   %a = add i32 %add, 128
@@ -76,12 +75,11 @@
 
 define <4 x i16> @testv4i32i16i8(<4 x i32> %add) {
 ; CHECK-LABEL: @testv4i32i16i8(
-; CHECK-NEXT:    [[A:%.*]] = add <4 x i32> [[ADD:%.*]], <i32 128, i32 128, i32 128, i32 128>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult <4 x i32> [[A]], <i32 256, i32 256, i32 256, i32 256>
-; CHECK-NEXT:    [[T:%.*]] = trunc <4 x i32> [[ADD]] to <4 x i16>
-; CHECK-NEXT:    [[C:%.*]] = icmp sgt <4 x i32> [[ADD]], <i32 -1, i32 -1, i32 -1, i32 -1>
-; CHECK-NEXT:    [[F:%.*]] = select <4 x i1> [[C]], <4 x i16> <i16 127, i16 127, i16 127, i16 127>, <4 x i16> <i16 -128, i16 -128, i16 -128, i16 -128>
-; CHECK-NEXT:    [[R:%.*]] = select <4 x i1> [[CMP]], <4 x i16> [[T]], <4 x i16> [[F]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp sgt <4 x i32> [[ADD:%.*]], <i32 -128, i32 -128, i32 -128, i32 -128>
+; CHECK-NEXT:    [[TMP2:%.*]] = select <4 x i1> [[TMP1]], <4 x i32> [[ADD]], <4 x i32> <i32 -128, i32 -128, i32 -128, i32 -128>
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp slt <4 x i32> [[TMP2]], <i32 127, i32 127, i32 127, i32 127>
+; CHECK-NEXT:    [[TMP4:%.*]] = select <4 x i1> [[TMP3]], <4 x i32> [[TMP2]], <4 x i32> <i32 127, i32 127, i32 127, i32 127>
+; CHECK-NEXT:    [[R:%.*]] = trunc <4 x i32> [[TMP4]] to <4 x i16>
 ; CHECK-NEXT:    ret <4 x i16> [[R]]
 ;
   %a = add <4 x i32> %add, <i32 128, i32 128, i32 128, i32 128>
@@ -310,12 +308,11 @@
 
 define i16 @differentconsts(i32 %x, i16 %replacement_low, i16 %replacement_high) {
 ; CHECK-LABEL: @differentconsts(
-; CHECK-NEXT:    [[T0:%.*]] = icmp slt i32 [[X:%.*]], 128
-; CHECK-NEXT:    [[T1:%.*]] = select i1 [[T0]], i16 256, i16 -1
-; CHECK-NEXT:    [[T2:%.*]] = add i32 [[X]], 16
-; CHECK-NEXT:    [[T3:%.*]] = icmp ult i32 [[T2]], 144
-; CHECK-NEXT:    [[T4:%.*]] = trunc i32 [[X]] to i16
-; CHECK-NEXT:    [[R:%.*]] = select i1 [[T3]], i16 [[T4]], i16 [[T1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt i32 [[X:%.*]], -16
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp sgt i32 [[X]], 127
+; CHECK-NEXT:    [[TMP3:%.*]] = trunc i32 [[X]] to i16
+; CHECK-NEXT:    [[TMP4:%.*]] = select i1 [[TMP1]], i16 256, i16 [[TMP3]]
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[TMP2]], i16 -1, i16 [[TMP4]]
 ; CHECK-NEXT:    ret i16 [[R]]
 ;
   %t0 = icmp slt i32 %x, 128