Index: llvm/lib/Analysis/Loads.cpp
===================================================================
--- llvm/lib/Analysis/Loads.cpp
+++ llvm/lib/Analysis/Loads.cpp
@@ -513,6 +513,39 @@
         return ConstantFoldLoadFromConst(C, AccessTy, DL);
   }
 
+  if (auto *MSI = dyn_cast<MemSetInst>(Inst)) {
+    // Don't forward from (non-atomic) memset to atomic load.
+    if (AtLeastAtomic)
+      return nullptr;
+
+    // Only handle constant memsets.
+    auto *Val = dyn_cast<ConstantInt>(MSI->getValue());
+    auto *Len = dyn_cast<ConstantInt>(MSI->getLength());
+    if (!Val || !Len)
+      return nullptr;
+
+    // TODO: Handle offsets.
+    Value *Dst = MSI->getDest();
+    if (!AreEquivalentAddressValues(Dst, Ptr))
+      return nullptr;
+
+    if (IsLoadCSE)
+      *IsLoadCSE = false;
+
+    // Make sure the read bytes are contained in the memset.
+    TypeSize LoadSize = DL.getTypeSizeInBits(AccessTy);
+    if (LoadSize.isScalable() ||
+        (Len->getValue() * 8).ult(LoadSize.getFixedSize()))
+      return nullptr;
+
+    APInt Splat = APInt::getSplat(LoadSize.getFixedSize(), Val->getValue());
+    ConstantInt *SplatC = ConstantInt::get(MSI->getContext(), Splat);
+    if (CastInst::isBitOrNoopPointerCastable(SplatC->getType(), AccessTy, DL))
+      return SplatC;
+
+    return nullptr;
+  }
+
   return nullptr;
 }
 
Index: llvm/test/Transforms/InstCombine/load-store-forward.ll
===================================================================
--- llvm/test/Transforms/InstCombine/load-store-forward.ll
+++ llvm/test/Transforms/InstCombine/load-store-forward.ll
@@ -257,8 +257,7 @@
 define i32 @load_after_memset_0(ptr %a) {
 ; CHECK-LABEL: @load_after_memset_0(
 ; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr noundef nonnull align 1 dereferenceable(16) [[A:%.*]], i8 0, i64 16, i1 false)
-; CHECK-NEXT:    [[V:%.*]] = load i32, ptr [[A]], align 4
-; CHECK-NEXT:    ret i32 [[V]]
+; CHECK-NEXT:    ret i32 0
 ;
   call void @llvm.memset.p0.i64(ptr %a, i8 0, i64 16, i1 false)
   %v = load i32, ptr %a
@@ -268,8 +267,7 @@
 define float @load_after_memset_0_float(ptr %a) {
 ; CHECK-LABEL: @load_after_memset_0_float(
 ; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr noundef nonnull align 1 dereferenceable(16) [[A:%.*]], i8 0, i64 16, i1 false)
-; CHECK-NEXT:    [[V:%.*]] = load float, ptr [[A]], align 4
-; CHECK-NEXT:    ret float [[V]]
+; CHECK-NEXT:    ret float 0.000000e+00
 ;
   call void @llvm.memset.p0.i64(ptr %a, i8 0, i64 16, i1 false)
   %v = load float, ptr %a
@@ -279,8 +277,7 @@
 define i27 @load_after_memset_0_non_byte_sized(ptr %a) {
 ; CHECK-LABEL: @load_after_memset_0_non_byte_sized(
 ; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr noundef nonnull align 1 dereferenceable(16) [[A:%.*]], i8 0, i64 16, i1 false)
-; CHECK-NEXT:    [[V:%.*]] = load i27, ptr [[A]], align 4
-; CHECK-NEXT:    ret i27 [[V]]
+; CHECK-NEXT:    ret i27 0
 ;
   call void @llvm.memset.p0.i64(ptr %a, i8 0, i64 16, i1 false)
   %v = load i27, ptr %a
@@ -290,8 +287,7 @@
 define <4 x i8> @load_after_memset_0_vec(ptr %a) {
 ; CHECK-LABEL: @load_after_memset_0_vec(
 ; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr noundef nonnull align 1 dereferenceable(16) [[A:%.*]], i8 0, i64 16, i1 false)
-; CHECK-NEXT:    [[V:%.*]] = load <4 x i8>, ptr [[A]], align 4
-; CHECK-NEXT:    ret <4 x i8> [[V]]
+; CHECK-NEXT:    ret <4 x i8> zeroinitializer
 ;
   call void @llvm.memset.p0.i64(ptr %a, i8 0, i64 16, i1 false)
   %v = load <4 x i8>, ptr %a
@@ -301,8 +297,7 @@
 define i32 @load_after_memset_1(ptr %a) {
 ; CHECK-LABEL: @load_after_memset_1(
 ; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr noundef nonnull align 1 dereferenceable(16) [[A:%.*]], i8 1, i64 16, i1 false)
-; CHECK-NEXT:    [[V:%.*]] = load i32, ptr [[A]], align 4
-; CHECK-NEXT:    ret i32 [[V]]
+; CHECK-NEXT:    ret i32 16843009
 ;
   call void @llvm.memset.p0.i64(ptr %a, i8 1, i64 16, i1 false)
   %v = load i32, ptr %a
@@ -312,8 +307,7 @@
 define float @load_after_memset_1_float(ptr %a) {
 ; CHECK-LABEL: @load_after_memset_1_float(
 ; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr noundef nonnull align 1 dereferenceable(16) [[A:%.*]], i8 1, i64 16, i1 false)
-; CHECK-NEXT:    [[V:%.*]] = load float, ptr [[A]], align 4
-; CHECK-NEXT:    ret float [[V]]
+; CHECK-NEXT:    ret float 0x3820202020000000
 ;
   call void @llvm.memset.p0.i64(ptr %a, i8 1, i64 16, i1 false)
   %v = load float, ptr %a
@@ -323,8 +317,7 @@
 define i27 @load_after_memset_1_non_byte_sized(ptr %a) {
 ; CHECK-LABEL: @load_after_memset_1_non_byte_sized(
 ; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr noundef nonnull align 1 dereferenceable(16) [[A:%.*]], i8 1, i64 16, i1 false)
-; CHECK-NEXT:    [[V:%.*]] = load i27, ptr [[A]], align 4
-; CHECK-NEXT:    ret i27 [[V]]
+; CHECK-NEXT:    ret i27 16843009
 ;
   call void @llvm.memset.p0.i64(ptr %a, i8 1, i64 16, i1 false)
   %v = load i27, ptr %a
@@ -334,8 +327,7 @@
 define <4 x i8> @load_after_memset_1_vec(ptr %a) {
 ; CHECK-LABEL: @load_after_memset_1_vec(
 ; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr noundef nonnull align 1 dereferenceable(16) [[A:%.*]], i8 1, i64 16, i1 false)
-; CHECK-NEXT:    [[V:%.*]] = load <4 x i8>, ptr [[A]], align 4
-; CHECK-NEXT:    ret <4 x i8> [[V]]
+; CHECK-NEXT:    ret <4 x i8> <i8 1, i8 1, i8 1, i8 1>
 ;
   call void @llvm.memset.p0.i64(ptr %a, i8 1, i64 16, i1 false)
   %v = load <4 x i8>, ptr %a
@@ -353,6 +345,7 @@
   ret i32 %v
 }
 
+; TODO: Handle load at offset.
 define i32 @load_after_memset_0_offset(ptr %a) {
 ; CHECK-LABEL: @load_after_memset_0_offset(
 ; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr noundef nonnull align 1 dereferenceable(16) [[A:%.*]], i8 0, i64 16, i1 false)