Index: llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -1161,6 +1161,17 @@
       return I->getOperand(0);
     }
 
+    // If we only demand the element that is being inserted and that element
+    // was extracted from the same index in another vector with the same type,
+    // replace this insert with that other vector.
+    Value *Vec;
+    if (PreInsertDemandedElts == 0 &&
+        match(I->getOperand(1),
+              m_ExtractElt(m_Value(Vec), m_SpecificInt(IdxNo))) &&
+        Vec->getType() == I->getType()) {
+      return Vec;
+    }
+
     // The inserted element is defined.
     UndefElts.clearBit(IdxNo);
     break;
Index: llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
===================================================================
--- llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
+++ llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
@@ -749,9 +749,7 @@
 
 define <4 x float> @ins_of_ext(<4 x float> %x, float %y) {
 ; CHECK-LABEL: @ins_of_ext(
-; CHECK-NEXT:    [[E0:%.*]] = extractelement <4 x float> [[X:%.*]], i32 0
-; CHECK-NEXT:    [[I0:%.*]] = insertelement <4 x float> undef, float [[E0]], i32 0
-; CHECK-NEXT:    [[I1:%.*]] = insertelement <4 x float> [[I0]], float [[Y:%.*]], i32 1
+; CHECK-NEXT:    [[I1:%.*]] = insertelement <4 x float> [[X:%.*]], float [[Y:%.*]], i32 1
 ; CHECK-NEXT:    [[I2:%.*]] = insertelement <4 x float> [[I1]], float [[Y]], i32 2
 ; CHECK-NEXT:    [[I3:%.*]] = insertelement <4 x float> [[I2]], float [[Y]], i32 3
 ; CHECK-NEXT:    ret <4 x float> [[I3]]
@@ -766,11 +764,7 @@
 
 define <4 x float> @ins_of_ext_twice(<4 x float> %x, float %y) {
 ; CHECK-LABEL: @ins_of_ext_twice(
-; CHECK-NEXT:    [[E0:%.*]] = extractelement <4 x float> [[X:%.*]], i32 0
-; CHECK-NEXT:    [[I0:%.*]] = insertelement <4 x float> undef, float [[E0]], i32 0
-; CHECK-NEXT:    [[E1:%.*]] = extractelement <4 x float> [[X]], i32 1
-; CHECK-NEXT:    [[I1:%.*]] = insertelement <4 x float> [[I0]], float [[E1]], i32 1
-; CHECK-NEXT:    [[I2:%.*]] = insertelement <4 x float> [[I1]], float [[Y:%.*]], i32 2
+; CHECK-NEXT:    [[I2:%.*]] = insertelement <4 x float> [[X:%.*]], float [[Y:%.*]], i32 2
 ; CHECK-NEXT:    [[I3:%.*]] = insertelement <4 x float> [[I2]], float [[Y]], i32 3
 ; CHECK-NEXT:    ret <4 x float> [[I3]]
 ;
@@ -783,6 +777,9 @@
   ret <4 x float> %i3
 }
 
+; Negative test - element 3 of the result must be undef to be poison safe.
+; TODO: Could convert insert/extract to identity shuffle with undef mask elements.
+
 define <4 x float> @ins_of_ext_wrong_demand(<4 x float> %x, float %y) {
 ; CHECK-LABEL: @ins_of_ext_wrong_demand(
 ; CHECK-NEXT:    [[E0:%.*]] = extractelement <4 x float> [[X:%.*]], i32 0
@@ -798,6 +795,9 @@
   ret <4 x float> %i2
 }
 
+; Negative test - can't replace i0 with x.
+; TODO: Could convert insert/extract to identity shuffle with undef mask elements.
+
 define <4 x float> @ins_of_ext_wrong_type(<5 x float> %x, float %y) {
 ; CHECK-LABEL: @ins_of_ext_wrong_type(
 ; CHECK-NEXT:    [[E0:%.*]] = extractelement <5 x float> [[X:%.*]], i32 0
Index: llvm/test/Transforms/SLPVectorizer/AArch64/getelementptr.ll
===================================================================
--- llvm/test/Transforms/SLPVectorizer/AArch64/getelementptr.ll
+++ llvm/test/Transforms/SLPVectorizer/AArch64/getelementptr.ll
@@ -51,13 +51,13 @@
 ; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <4 x i32> [[TMP1]], i32 [[Z:%.*]], i32 3
 ; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
 ; CHECK:       for.cond.cleanup.loopexit:
-; CHECK-NEXT:    [[TMP3:%.*]] = extractelement <2 x i32> [[TMP21:%.*]], i32 1
+; CHECK-NEXT:    [[TMP3:%.*]] = extractelement <2 x i32> [[TMP20:%.*]], i32 1
 ; CHECK-NEXT:    br label [[FOR_COND_CLEANUP]]
 ; CHECK:       for.cond.cleanup:
 ; CHECK-NEXT:    [[SUM_0_LCSSA:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[TMP3]], [[FOR_COND_CLEANUP_LOOPEXIT:%.*]] ]
 ; CHECK-NEXT:    ret i32 [[SUM_0_LCSSA]]
 ; CHECK:       for.body:
-; CHECK-NEXT:    [[TMP4:%.*]] = phi <2 x i32> [ zeroinitializer, [[FOR_BODY_PREHEADER]] ], [ [[TMP21]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[TMP4:%.*]] = phi <2 x i32> [ zeroinitializer, [[FOR_BODY_PREHEADER]] ], [ [[TMP20]], [[FOR_BODY]] ]
 ; CHECK-NEXT:    [[TMP5:%.*]] = extractelement <2 x i32> [[TMP4]], i32 0
 ; CHECK-NEXT:    [[T4:%.*]] = shl nsw i32 [[TMP5]], 1
 ; CHECK-NEXT:    [[TMP6:%.*]] = insertelement <4 x i32> undef, i32 [[T4]], i32 0
@@ -83,12 +83,11 @@
 ; CHECK-NEXT:    [[TMP17:%.*]] = sext i32 [[TMP16]] to i64
 ; CHECK-NEXT:    [[ARRAYIDX15:%.*]] = getelementptr inbounds i32, i32* [[G]], i64 [[TMP17]]
 ; CHECK-NEXT:    [[T12:%.*]] = load i32, i32* [[ARRAYIDX15]], align 4
-; CHECK-NEXT:    [[TMP18:%.*]] = insertelement <2 x i32> undef, i32 [[TMP5]], i32 0
-; CHECK-NEXT:    [[TMP19:%.*]] = insertelement <2 x i32> [[TMP18]], i32 [[ADD11]], i32 1
-; CHECK-NEXT:    [[TMP20:%.*]] = insertelement <2 x i32> <i32 1, i32 undef>, i32 [[T12]], i32 1
-; CHECK-NEXT:    [[TMP21]] = add nsw <2 x i32> [[TMP19]], [[TMP20]]
-; CHECK-NEXT:    [[TMP22:%.*]] = extractelement <2 x i32> [[TMP21]], i32 0
-; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp eq i32 [[TMP22]], [[N]]
+; CHECK-NEXT:    [[TMP18:%.*]] = insertelement <2 x i32> [[TMP4]], i32 [[ADD11]], i32 1
+; CHECK-NEXT:    [[TMP19:%.*]] = insertelement <2 x i32> <i32 1, i32 undef>, i32 [[T12]], i32 1
+; CHECK-NEXT:    [[TMP20]] = add nsw <2 x i32> [[TMP18]], [[TMP19]]
+; CHECK-NEXT:    [[TMP21:%.*]] = extractelement <2 x i32> [[TMP20]], i32 0
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp eq i32 [[TMP21]], [[N]]
 ; CHECK-NEXT:    br i1 [[EXITCOND]], label [[FOR_COND_CLEANUP_LOOPEXIT]], label [[FOR_BODY]]
 ;
 entry:
@@ -157,13 +156,13 @@
 ; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <2 x i32> [[TMP0]], i32 [[Z:%.*]], i32 1
 ; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
 ; CHECK:       for.cond.cleanup.loopexit:
-; CHECK-NEXT:    [[TMP2:%.*]] = extractelement <2 x i32> [[TMP18:%.*]], i32 1
+; CHECK-NEXT:    [[TMP2:%.*]] = extractelement <2 x i32> [[TMP17:%.*]], i32 1
 ; CHECK-NEXT:    br label [[FOR_COND_CLEANUP]]
 ; CHECK:       for.cond.cleanup:
 ; CHECK-NEXT:    [[SUM_0_LCSSA:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[TMP2]], [[FOR_COND_CLEANUP_LOOPEXIT:%.*]] ]
 ; CHECK-NEXT:    ret i32 [[SUM_0_LCSSA]]
 ; CHECK:       for.body:
-; CHECK-NEXT:    [[TMP3:%.*]] = phi <2 x i32> [ zeroinitializer, [[FOR_BODY_PREHEADER]] ], [ [[TMP18]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[TMP3:%.*]] = phi <2 x i32> [ zeroinitializer, [[FOR_BODY_PREHEADER]] ], [ [[TMP17]], [[FOR_BODY]] ]
 ; CHECK-NEXT:    [[TMP4:%.*]] = extractelement <2 x i32> [[TMP3]], i32 0
 ; CHECK-NEXT:    [[T4:%.*]] = shl nsw i32 [[TMP4]], 1
 ; CHECK-NEXT:    [[TMP5:%.*]] = sext i32 [[T4]] to i64
@@ -188,12 +187,11 @@
 ; CHECK-NEXT:    [[TMP14:%.*]] = sext i32 [[TMP13]] to i64
 ; CHECK-NEXT:    [[ARRAYIDX15:%.*]] = getelementptr inbounds i32, i32* [[G]], i64 [[TMP14]]
 ; CHECK-NEXT:    [[T12:%.*]] = load i32, i32* [[ARRAYIDX15]], align 4
-; CHECK-NEXT:    [[TMP15:%.*]] = insertelement <2 x i32> undef, i32 [[TMP4]], i32 0
-; CHECK-NEXT:    [[TMP16:%.*]] = insertelement <2 x i32> [[TMP15]], i32 [[ADD11]], i32 1
-; CHECK-NEXT:    [[TMP17:%.*]] = insertelement <2 x i32> <i32 1, i32 undef>, i32 [[T12]], i32 1
-; CHECK-NEXT:    [[TMP18]] = add nsw <2 x i32> [[TMP16]], [[TMP17]]
-; CHECK-NEXT:    [[TMP19:%.*]] = extractelement <2 x i32> [[TMP18]], i32 0
-; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp eq i32 [[TMP19]], [[N]]
+; CHECK-NEXT:    [[TMP15:%.*]] = insertelement <2 x i32> [[TMP3]], i32 [[ADD11]], i32 1
+; CHECK-NEXT:    [[TMP16:%.*]] = insertelement <2 x i32> <i32 1, i32 undef>, i32 [[T12]], i32 1
+; CHECK-NEXT:    [[TMP17]] = add nsw <2 x i32> [[TMP15]], [[TMP16]]
+; CHECK-NEXT:    [[TMP18:%.*]] = extractelement <2 x i32> [[TMP17]], i32 0
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp eq i32 [[TMP18]], [[N]]
 ; CHECK-NEXT:    br i1 [[EXITCOND]], label [[FOR_COND_CLEANUP_LOOPEXIT]], label [[FOR_BODY]]
 ;
 entry:
Index: llvm/test/Transforms/SLPVectorizer/X86/operandorder.ll
===================================================================
--- llvm/test/Transforms/SLPVectorizer/X86/operandorder.ll
+++ llvm/test/Transforms/SLPVectorizer/X86/operandorder.ll
@@ -183,13 +183,11 @@
 ; CHECK-NEXT:    [[P:%.*]] = phi double [ 1.000000e+00, [[LP]] ], [ 0.000000e+00, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    [[TMP0:%.*]] = bitcast double* [[FROM:%.*]] to <2 x double>*
 ; CHECK-NEXT:    [[TMP1:%.*]] = load <2 x double>, <2 x double>* [[TMP0]], align 4
-; CHECK-NEXT:    [[TMP2:%.*]] = extractelement <2 x double> [[TMP1]], i32 0
-; CHECK-NEXT:    [[TMP3:%.*]] = insertelement <2 x double> undef, double [[TMP2]], i32 0
-; CHECK-NEXT:    [[TMP4:%.*]] = insertelement <2 x double> [[TMP3]], double [[P]], i32 1
-; CHECK-NEXT:    [[TMP5:%.*]] = shufflevector <2 x double> [[TMP1]], <2 x double> undef, <2 x i32> <i32 1, i32 0>
-; CHECK-NEXT:    [[TMP6:%.*]] = fadd <2 x double> [[TMP4]], [[TMP5]]
-; CHECK-NEXT:    [[TMP7:%.*]] = bitcast double* [[TO:%.*]] to <2 x double>*
-; CHECK-NEXT:    store <2 x double> [[TMP6]], <2 x double>* [[TMP7]], align 4
+; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <2 x double> [[TMP1]], double [[P]], i32 1
+; CHECK-NEXT:    [[TMP3:%.*]] = shufflevector <2 x double> [[TMP1]], <2 x double> undef, <2 x i32> <i32 1, i32 0>
+; CHECK-NEXT:    [[TMP4:%.*]] = fadd <2 x double> [[TMP2]], [[TMP3]]
+; CHECK-NEXT:    [[TMP5:%.*]] = bitcast double* [[TO:%.*]] to <2 x double>*
+; CHECK-NEXT:    store <2 x double> [[TMP4]], <2 x double>* [[TMP5]], align 4
 ; CHECK-NEXT:    br i1 undef, label [[LP]], label [[EXT:%.*]]
 ; CHECK:       ext:
 ; CHECK-NEXT:    ret void