Index: include/llvm/Bitcode/LLVMBitCodes.h
===================================================================
--- include/llvm/Bitcode/LLVMBitCodes.h
+++ include/llvm/Bitcode/LLVMBitCodes.h
@@ -402,6 +402,20 @@
   OBO_NO_SIGNED_WRAP = 1
 };
 
+/// FastMath Flags
+/// This is a fixed layout derived from the bitcode emitted by LLVM 5.0
+/// intended to decouple the in-memory representation from the serialization.
+enum FastMathMap {
+  UnsafeAlgebra   = (1 << 0), // Legacy
+  NoNaNs          = (1 << 1),
+  NoInfs          = (1 << 2),
+  NoSignedZeros   = (1 << 3),
+  AllowReciprocal = (1 << 4),
+  AllowContract   = (1 << 5),
+  ApproxFunc      = (1 << 6),
+  AllowReassoc    = (1 << 7)
+};
+
 /// PossiblyExactOperatorOptionalFlags - Flags for serializing
 /// PossiblyExactOperator's SubclassOptionalData contents.
 enum PossiblyExactOperatorOptionalFlags { PEO_EXACT = 0 };
Index: lib/Bitcode/Reader/BitcodeReader.cpp
===================================================================
--- lib/Bitcode/Reader/BitcodeReader.cpp
+++ lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1047,19 +1047,21 @@
 
 static FastMathFlags getDecodedFastMathFlags(unsigned Val) {
   FastMathFlags FMF;
-  if (0 != (Val & FastMathFlags::AllowReassoc))
+  if (0 != (Val & bitc::UnsafeAlgebra))
+    FMF.setFast();
+  if (0 != (Val & bitc::AllowReassoc))
     FMF.setAllowReassoc();
-  if (0 != (Val & FastMathFlags::NoNaNs))
+  if (0 != (Val & bitc::NoNaNs))
     FMF.setNoNaNs();
-  if (0 != (Val & FastMathFlags::NoInfs))
+  if (0 != (Val & bitc::NoInfs))
     FMF.setNoInfs();
-  if (0 != (Val & FastMathFlags::NoSignedZeros))
+  if (0 != (Val & bitc::NoSignedZeros))
     FMF.setNoSignedZeros();
-  if (0 != (Val & FastMathFlags::AllowReciprocal))
+  if (0 != (Val & bitc::AllowReciprocal))
     FMF.setAllowReciprocal();
-  if (0 != (Val & FastMathFlags::AllowContract))
+  if (0 != (Val & bitc::AllowContract))
     FMF.setAllowContract(true);
-  if (0 != (Val & FastMathFlags::ApproxFunc))
+  if (0 != (Val & bitc::ApproxFunc))
     FMF.setApproxFunc();
   return FMF;
 }
Index: lib/Bitcode/Writer/BitcodeWriter.cpp
===================================================================
--- lib/Bitcode/Writer/BitcodeWriter.cpp
+++ lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -1334,19 +1334,19 @@
       Flags |= 1 << bitc::PEO_EXACT;
   } else if (const auto *FPMO = dyn_cast<FPMathOperator>(V)) {
     if (FPMO->hasAllowReassoc())
-      Flags |= FastMathFlags::AllowReassoc;
+      Flags |= bitc::AllowReassoc;
     if (FPMO->hasNoNaNs())
-      Flags |= FastMathFlags::NoNaNs;
+      Flags |= bitc::NoNaNs;
     if (FPMO->hasNoInfs())
-      Flags |= FastMathFlags::NoInfs;
+      Flags |= bitc::NoInfs;
     if (FPMO->hasNoSignedZeros())
-      Flags |= FastMathFlags::NoSignedZeros;
+      Flags |= bitc::NoSignedZeros;
     if (FPMO->hasAllowReciprocal())
-      Flags |= FastMathFlags::AllowReciprocal;
+      Flags |= bitc::AllowReciprocal;
     if (FPMO->hasAllowContract())
-      Flags |= FastMathFlags::AllowContract;
+      Flags |= bitc::AllowContract;
     if (FPMO->hasApproxFunc())
-      Flags |= FastMathFlags::ApproxFunc;
+      Flags |= bitc::ApproxFunc;
   }
 
   return Flags;
@@ -3196,7 +3196,7 @@
     Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // LHS
     Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // RHS
     Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 4)); // opc
-    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 7)); // flags
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 8)); // flags
     if (Stream.EmitBlockInfoAbbrev(bitc::FUNCTION_BLOCK_ID, Abbv) !=
         FUNCTION_INST_BINOP_FLAGS_ABBREV)
       llvm_unreachable("Unexpected abbrev ordering!");
Index: test/Bitcode/compatibility-3.6.ll
===================================================================
--- test/Bitcode/compatibility-3.6.ll
+++ test/Bitcode/compatibility-3.6.ll
@@ -614,7 +614,7 @@
   %f.fast = fadd fast float %op1, %op2
   ; 'fast' used to be its own bit, but this changed in Oct 2017.
   ; The binary test file does not have the newer 'contract' and 'afn' bits set, so this is not fully 'fast'.
-  ; CHECK: %f.fast = fadd reassoc nnan ninf nsz arcp float %op1, %op2
+  ; CHECK: %f.fast = fadd fast float %op1, %op2
   ret void
 }
 
Index: test/Bitcode/compatibility-3.7.ll
===================================================================
--- test/Bitcode/compatibility-3.7.ll
+++ test/Bitcode/compatibility-3.7.ll
@@ -658,7 +658,7 @@
   %f.fast = fadd fast float %op1, %op2
   ; 'fast' used to be its own bit, but this changed in Oct 2017.
   ; The binary test file does not have the newer 'contract' and 'afn' bits set, so this is not fully 'fast'.
-  ; CHECK: %f.fast = fadd reassoc nnan ninf nsz arcp float %op1, %op2
+  ; CHECK: %f.fast = fadd fast float %op1, %op2
   ret void
 }
 
Index: test/Bitcode/compatibility-3.8.ll
===================================================================
--- test/Bitcode/compatibility-3.8.ll
+++ test/Bitcode/compatibility-3.8.ll
@@ -689,7 +689,7 @@
   %f.fast = fadd fast float %op1, %op2
   ; 'fast' used to be its own bit, but this changed in Oct 2017.
   ; The binary test file does not have the newer 'contract' and 'afn' bits set, so this is not fully 'fast'.
-  ; CHECK: %f.fast = fadd reassoc nnan ninf nsz arcp float %op1, %op2
+  ; CHECK: %f.fast = fadd fast float %op1, %op2
   ret void
 }
 
@@ -704,7 +704,7 @@
   %call.fast = call fast float @fmf1()
   ; 'fast' used to be its own bit, but this changed in Oct 2017.
   ; The binary test file does not have the newer 'contract' and 'aml' bits set, so this is not fully 'fast'.
-  ; CHECK: %call.fast = call reassoc nnan ninf nsz arcp float @fmf1()
+  ; CHECK: %call.fast = call fast float @fmf1()
 
   ; Throw in some other attributes to make sure those stay in the right places.
 
Index: test/Bitcode/compatibility-3.9.ll
===================================================================
--- test/Bitcode/compatibility-3.9.ll
+++ test/Bitcode/compatibility-3.9.ll
@@ -760,7 +760,7 @@
   %f.fast = fadd fast float %op1, %op2
   ; 'fast' used to be its own bit, but this changed in Oct 2017.
   ; The binary test file does not have the newer 'contract' and 'afn' bits set, so this is not fully 'fast'.
-  ; CHECK: %f.fast = fadd reassoc nnan ninf nsz arcp float %op1, %op2
+  ; CHECK: %f.fast = fadd fast float %op1, %op2
   ret void
 }
 
@@ -775,7 +775,7 @@
   %call.fast = call fast float @fmf1()
   ; 'fast' used to be its own bit, but this changed in Oct 2017.
   ; The binary test file does not have the newer 'contract' and 'afn' bits set, so this is not fully 'fast'.
-  ; CHECK: %call.fast = call reassoc nnan ninf nsz arcp float @fmf1()
+  ; CHECK: %call.fast = call fast float @fmf1()
 
   ; Throw in some other attributes to make sure those stay in the right places.
 
Index: test/Bitcode/compatibility-4.0.ll
===================================================================
--- test/Bitcode/compatibility-4.0.ll
+++ test/Bitcode/compatibility-4.0.ll
@@ -760,7 +760,7 @@
   ; 'fast' used to be its own bit, but this changed in Oct 2017.
   ; The binary test file does not have the newer 'contract' and 'afn' bits set, so this is not fully 'fast'.
   %f.fast = fadd fast float %op1, %op2
-  ; CHECK: %f.fast = fadd reassoc nnan ninf nsz arcp float %op1, %op2
+  ; CHECK: %f.fast = fadd fast float %op1, %op2
   ret void
 }
 
@@ -775,7 +775,7 @@
   %call.fast = call fast float @fmf1()
   ; 'fast' used to be its own bit, but this changed in Oct 2017.
   ; The binary test file does not have the newer 'contract' and 'afn' bits set, so this is not fully 'fast'.
-  ; CHECK: %call.fast = call reassoc nnan ninf nsz arcp float @fmf1()
+  ; CHECK: %call.fast = call fast float @fmf1()
 
   ; Throw in some other attributes to make sure those stay in the right places.
 
Index: test/Bitcode/compatibility-5.0.ll
===================================================================
--- test/Bitcode/compatibility-5.0.ll
+++ test/Bitcode/compatibility-5.0.ll
@@ -767,7 +767,7 @@
   %f.fast = fadd fast float %op1, %op2
   ; 'fast' used to be its own bit, but this changed in Oct 2017.
   ; The binary test file does not have the newer 'afn' bit set, so this is not fully 'fast'.
-  ; CHECK: %f.fast = fadd reassoc nnan ninf nsz arcp contract float %op1, %op2
+  ; CHECK: %f.fast = fadd fast float %op1, %op2
   ret void
 }
 
@@ -782,7 +782,7 @@
   %call.fast = call fast float @fmf1()
   ; 'fast' used to be its own bit, but this changed in Oct 2017.
   ; The binary test file does not have the newer 'afn' bit set, so this is not fully 'fast'.
-  ; CHECK: %call.fast = call reassoc nnan ninf nsz arcp contract float @fmf1()
+  ; CHECK: %call.fast = call fast float @fmf1()
 
   ; Throw in some other attributes to make sure those stay in the right places.