diff --git a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
--- a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -893,11 +893,14 @@
 static bool areOuterLoopExitPHIsSupported(Loop *OuterLoop, Loop *InnerLoop) {
   BasicBlock *LoopNestExit = OuterLoop->getUniqueExitBlock();
   for (PHINode &PHI : LoopNestExit->phis()) {
-    //  FIXME: We currently are not able to detect floating point reductions
-    //         and have to use floating point PHIs as a proxy to prevent
-    //         interchanging in the presence of floating point reductions.
-    if (PHI.getType()->isFloatingPointTy())
-      return false;
+    // Support floating-point reduction only if we allow unsafe fp math.
+    if (PHI.getType()->isFloatingPointTy()) {
+      Function *F = OuterLoop->getHeader()->getParent();
+      Instruction *I = dyn_cast<Instruction>(followLCSSA(&PHI));
+      if (!F->getFnAttribute("unsafe-fp-math").getValueAsBool() ||
+          I == nullptr || !I->isFast())
+        return false;
+    }
     for (unsigned i = 0; i < PHI.getNumIncomingValues(); i++) {
      Instruction *IncomingI = dyn_cast<Instruction>(PHI.getIncomingValue(i));
      if (!IncomingI || IncomingI->getParent() != OuterLoop->getLoopLatch())
diff --git a/llvm/test/Transforms/LoopInterchange/lcssa.ll b/llvm/test/Transforms/LoopInterchange/lcssa.ll
--- a/llvm/test/Transforms/LoopInterchange/lcssa.ll
+++ b/llvm/test/Transforms/LoopInterchange/lcssa.ll
@@ -135,39 +135,41 @@
   ret void
 }
 
-; FIXME: We currently do not support LCSSA phi nodes involving floating point
-;        types, as we fail to detect floating point reductions for now.
-; REMARK: UnsupportedPHIOuter
+; Loops with floating point reductions are interchanged with fastmath.
+; REMARK: Interchanged
 ; REMARK-NEXT: lcssa_04
 
-define void @lcssa_04() {
+define void @lcssa_04() #0 {
 entry:
   br label %outer.header
 
 outer.header:                                     ; preds = %outer.inc, %entry
   %iv.outer = phi i64 [ 1, %entry ], [ %iv.outer.next, %outer.inc ]
-  %float.outer = phi float [ 1.000000e+00, %entry ], [ 2.000000e+00, %outer.inc ]
+  %float.outer = phi float [ 1.000000e+00, %entry ], [ %float.outer.next, %outer.inc ]
   br label %for.body3
 
 for.body3:                                        ; preds = %for.body3, %outer.header
   %iv.inner = phi i64 [ %iv.inner.next, %for.body3 ], [ 1, %outer.header ]
+  %float.inner = phi float [ %float.inner.next, %for.body3 ], [ %float.outer, %outer.header ]
   %arrayidx5 = getelementptr inbounds [100 x [100 x i32]], [100 x [100 x i32]]* @A, i64 0, i64 %iv.inner, i64 %iv.outer
   %vA = load i32, i32* %arrayidx5
   %arrayidx9 = getelementptr inbounds [100 x [100 x i32]], [100 x [100 x i32]]* @C, i64 0, i64 %iv.inner, i64 %iv.outer
   %vC = load i32, i32* %arrayidx9
   %add = add nsw i32 %vA, %vC
+  %float.inner.next = fadd fast float %float.inner, 1.000000e+00
   store i32 %add, i32* %arrayidx5
   %iv.inner.next = add nuw nsw i64 %iv.inner, 1
   %exitcond = icmp eq i64 %iv.inner.next, 100
   br i1 %exitcond, label %outer.inc, label %for.body3
 
 outer.inc:                                        ; preds = %for.body3
+  %float.outer.next = phi float [ %float.inner.next, %for.body3 ]
   %iv.outer.next = add nsw i64 %iv.outer, 1
   %cmp = icmp eq i64 %iv.outer.next, 100
   br i1 %cmp, label %outer.header, label %for.exit
 
 for.exit:                                         ; preds = %outer.inc
-  %float.outer.lcssa = phi float [ %float.outer, %outer.inc ]
+  %float.outer.lcssa = phi float [ %float.outer.next, %outer.inc ]
   store float %float.outer.lcssa, float* @F
   br label %for.end16
 
@@ -175,6 +177,8 @@
   ret void
 }
 
+attributes #0 = {"unsafe-fp-math"="true" }
+
 ; PHI node in inner latch with multiple predecessors.
 ; REMARK: Interchanged
 ; REMARK-NEXT: lcssa_05
diff --git a/llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll b/llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll
--- a/llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll
+++ b/llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll
@@ -189,3 +189,77 @@
   %il.res.lcssa2 = phi i64 [ %sum.inc.amend, %for1.inc ]
   ret i64 %il.res.lcssa2
 }
+
+; Floating point reductions are interchanged with fast-math.
+; REMARKS: --- !Passed
+; REMARKS-NEXT: Pass:            loop-interchange
+; REMARKS-NEXT: Name:            Interchanged
+; REMARKS-NEXT: Function:        test4
+
+define float @test4([100 x [100 x float]]* %Arr) #0 {
+entry:
+  br label %outer.header
+
+outer.header:                                     ; preds = %outer.inc, %entry
+  %iv.outer = phi i64 [ 1, %entry ], [ %iv.outer.next, %outer.inc ]
+  %float.outer = phi float [ 1.000000e+00, %entry ], [ %float.inner.lcssa, %outer.inc ]
+  br label %for.body3
+
+for.body3:                                        ; preds = %for.body3, %outer.header
+  %float.inner = phi float [ %float.outer , %outer.header ], [ %float.inner.inc, %for.body3 ]
+  %iv.inner = phi i64 [ %iv.inner.next, %for.body3 ], [ 1, %outer.header ]
+  %arrayidx5 = getelementptr inbounds [100 x [100 x float]], [100 x [100 x float]]* %Arr, i64 0, i64 %iv.inner, i64 %iv.outer
+  %vA = load float, float* %arrayidx5
+  %float.inner.inc = fadd fast float %float.inner, %vA
+  %iv.inner.next = add nuw nsw i64 %iv.inner, 1
+  %exitcond = icmp eq i64 %iv.inner.next, 100
+  br i1 %exitcond, label %outer.inc, label %for.body3
+
+outer.inc:                                        ; preds = %for.body3
+  %float.inner.lcssa = phi float [ %float.inner.inc, %for.body3 ]
+  %iv.outer.next = add nsw i64 %iv.outer, 1
+  %cmp = icmp eq i64 %iv.outer.next, 100
+  br i1 %cmp, label %outer.header, label %for.exit
+
+for.exit:                                         ; preds = %outer.inc
+  %float.outer.lcssa = phi float [ %float.inner.lcssa, %outer.inc ]
+  ret float %float.outer.lcssa
+}
+
+attributes #0 = {"unsafe-fp-math"="true" }
+
+; Floating point reductions are not interchanged without fast-math.
+; REMARKS: --- !Missed
+; REMARKS-NEXT: Pass:            loop-interchange
+; REMARKS-NEXT: Name:            UnsupportedExitPHI
+; REMARKS-NEXT: Function:        test5
+
+define float @test5([100 x [100 x float]]* %Arr) {
+entry:
+  br label %outer.header
+
+outer.header:                                     ; preds = %outer.inc, %entry
+  %iv.outer = phi i64 [ 1, %entry ], [ %iv.outer.next, %outer.inc ]
+  %float.outer = phi float [ 1.000000e+00, %entry ], [ %float.inner.lcssa, %outer.inc ]
+  br label %for.body3
+
+for.body3:                                        ; preds = %for.body3, %outer.header
+  %float.inner = phi float [ %float.outer , %outer.header ], [ %float.inner.inc, %for.body3 ]
+  %iv.inner = phi i64 [ %iv.inner.next, %for.body3 ], [ 1, %outer.header ]
+  %arrayidx5 = getelementptr inbounds [100 x [100 x float]], [100 x [100 x float]]* %Arr, i64 0, i64 %iv.inner, i64 %iv.outer
+  %vA = load float, float* %arrayidx5
+  %float.inner.inc = fadd float %float.inner, %vA
+  %iv.inner.next = add nuw nsw i64 %iv.inner, 1
+  %exitcond = icmp eq i64 %iv.inner.next, 100
+  br i1 %exitcond, label %outer.inc, label %for.body3
+
+outer.inc:                                        ; preds = %for.body3
+  %float.inner.lcssa = phi float [ %float.inner.inc, %for.body3 ]
+  %iv.outer.next = add nsw i64 %iv.outer, 1
+  %cmp = icmp eq i64 %iv.outer.next, 100
+  br i1 %cmp, label %outer.header, label %for.exit
+
+for.exit:                                         ; preds = %outer.inc
+  %float.outer.lcssa = phi float [ %float.inner.lcssa, %outer.inc ]
+  ret float %float.outer.lcssa
+}
\ No newline at end of file