Index: lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1394,39 +1394,52 @@
   // integer add followed by a promotion.
   if (SIToFPInst *LHSConv = dyn_cast<SIToFPInst>(LHS)) {
     Value *LHSIntVal = LHSConv->getOperand(0);
+    Type *FPType = LHSConv->getType();
+
+    auto IsValidPromotion = [] (Type *FTy, Type *ITy) {
+      // Do we have enough bits in the significand to represent the result of the
+      // integer addition?
+      unsigned MaxRepresentableBits
+        = APFloat::semanticsPrecision(FTy->getFltSemantics());
+      return ITy->getIntegerBitWidth() <= MaxRepresentableBits;
+    };
 
     // (fadd double (sitofp x), fpcst) --> (sitofp (add int x, intcst))
     // ... if the constant fits in the integer value.  This is useful for things
     // like (double)(x & 1234) + 4.0 -> (double)((X & 1234)+4) which no longer
     // requires a constant pool load, and generally allows the add to be better
     // instcombined.
-    if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHS)) {
-      Constant *CI =
-      ConstantExpr::getFPToSI(CFP, LHSIntVal->getType());
-      if (LHSConv->hasOneUse() &&
-          ConstantExpr::getSIToFP(CI, I.getType()) == CFP &&
-          WillNotOverflowSignedAdd(LHSIntVal, CI, I)) {
-        // Insert the new integer add.
-        Value *NewAdd = Builder->CreateNSWAdd(LHSIntVal,
-                                              CI, "addconv");
-        return new SIToFPInst(NewAdd, I.getType());
+    if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHS))
+      if (IsValidPromotion(FPType, LHSIntVal->getType())) {
+        Constant *CI =
+          ConstantExpr::getFPToSI(CFP, LHSIntVal->getType());
+        if (LHSConv->hasOneUse() &&
+            ConstantExpr::getSIToFP(CI, I.getType()) == CFP &&
+            WillNotOverflowSignedAdd(LHSIntVal, CI, I)) {
+          // Insert the new integer add.
+          Value *NewAdd = Builder->CreateNSWAdd(LHSIntVal,
+                                                CI, "addconv");
+          return new SIToFPInst(NewAdd, I.getType());
+        }
       }
-    }
 
     // (fadd double (sitofp x), (sitofp y)) --> (sitofp (add int x, y))
     if (SIToFPInst *RHSConv = dyn_cast<SIToFPInst>(RHS)) {
       Value *RHSIntVal = RHSConv->getOperand(0);
-
-      // Only do this if x/y have the same type, if at last one of them has a
-      // single use (so we don't increase the number of int->fp conversions),
-      // and if the integer add will not overflow.
-      if (LHSIntVal->getType() == RHSIntVal->getType() &&
-          (LHSConv->hasOneUse() || RHSConv->hasOneUse()) &&
-          WillNotOverflowSignedAdd(LHSIntVal, RHSIntVal, I)) {
-        // Insert the new integer add.
-        Value *NewAdd = Builder->CreateNSWAdd(LHSIntVal,
-                                              RHSIntVal, "addconv");
-        return new SIToFPInst(NewAdd, I.getType());
+      // It's enough to check LHS types only because we require int types to
+      // be the same for this transform.
+      if (IsValidPromotion(FPType, LHSIntVal->getType())) {
+        // Only do this if x/y have the same type, if at last one of them has a
+        // single use (so we don't increase the number of int->fp conversions),
+        // and if the integer add will not overflow.
+        if (LHSIntVal->getType() == RHSIntVal->getType() &&
+            (LHSConv->hasOneUse() || RHSConv->hasOneUse()) &&
+            WillNotOverflowSignedAdd(LHSIntVal, RHSIntVal, I)) {
+          // Insert the new integer add.
+          Value *NewAdd = Builder->CreateNSWAdd(LHSIntVal,
+                                                RHSIntVal, "addconv");
+          return new SIToFPInst(NewAdd, I.getType());
+        }
       }
     }
   }
Index: test/Transforms/InstCombine/add-sitofp.ll
===================================================================
--- test/Transforms/InstCombine/add-sitofp.ll
+++ test/Transforms/InstCombine/add-sitofp.ll
@@ -1,9 +1,63 @@
-; RUN: opt < %s -instcombine -S | grep "add nuw nsw i32"
+; RUN: opt < %s -instcombine -S | FileCheck %s
 
 define double @x(i32 %a, i32 %b) nounwind {
+; CHECK-LABEL: @x
+; CHECK: add nuw nsw i32
   %m = lshr i32 %a, 24
   %n = and i32 %m, %b
   %o = sitofp i32 %n to double
   %p = fadd double %o, 1.0
   ret double %p
 }
+
+define double @test(i32 %a) nounwind {
+; CHECK-LABEL: @test
+; CHECK: add nuw nsw i32
+
+  ; Drop two highes bits to guarantee that %a + 1 doesn't overflow
+  %a_and = and i32 %a, 1073741823
+  %a_and_fp = sitofp i32 %a_and to double
+  %res = fadd double %a_and_fp, 1.0
+  ret double %res
+}
+
+define float @test_neg(i32 %a) nounwind {
+; CHECK-LABEL: @test_neg
+; CHECK: fadd float
+
+  ; Drop two highes bits to guarantee that %a + 1 doesn't overflow
+  %a_and = and i32 %a, 1073741823
+  %a_and_fp = sitofp i32 %a_and to float
+  %res = fadd float %a_and_fp, 1.0
+  ret float %res
+}
+
+define double @test_2(i32 %a, i32 %b) nounwind {
+; CHECK-LABEL: @test
+; CHECK: add nuw nsw i32
+
+  ; Drop two highes bits to guarantee that %a + %b doesn't overflow
+  %a_and = and i32 %a, 1073741823
+  %b_and = and i32 %b, 1073741823
+
+  %a_and_fp = sitofp i32 %a_and to double
+  %b_and_fp = sitofp i32 %b_and to double
+
+  %res = fadd double %a_and_fp, %b_and_fp
+  ret double %res
+}
+
+define float @test_2_neg(i32 %a, i32 %b) nounwind {
+; CHECK-LABEL: @test
+; CHECK: fadd float
+
+  ; Drop two highes bits to guarantee that %a + %b doesn't overflow
+  %a_and = and i32 %a, 1073741823
+  %b_and = and i32 %b, 1073741823
+
+  %a_and_fp = sitofp i32 %a_and to float
+  %b_and_fp = sitofp i32 %b_and to float
+
+  %res = fadd float %a_and_fp, %b_and_fp
+  ret float %res
+}
\ No newline at end of file