[IR] Add AllowContract to FastMathFlags

-ffp-contract=fast does not currently work with LTO because it's passed as a
TargetOption to the backend rather than in the IR. This adds it to
FastMathFlags.

This is toward fixing PR25721

Differential Revision: https://reviews.llvm.org/D31164

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298939 91177308-0d34-0410-b5e6-96231b3b80d8

docs/LangRef.rst

@@ -2194,6 +2194,10 @@ otherwise unsafe floating point transformations.
    Allow Reciprocal - Allow optimizations to use the reciprocal of an
    argument rather than perform division.
 
+``contract``
+   Allow floating-point contraction (e.g. fusing a multiply followed by an
+   addition into a fused multiply-and-add).
+
 ``fast``
    Fast - Allow algebraically equivalent transformations that may
    dramatically change results in floating point (e.g. reassociate). This

include/llvm/IR/Instruction.h

@@ -345,6 +345,9 @@ public:
   /// Determine whether the allow-reciprocal flag is set.
   bool hasAllowReciprocal() const;
 
+  /// Determine whether the allow-contract flag is set.
+  bool hasAllowContract() const;
+
   /// Convenience function for getting all the fast-math flags, which must be an
   /// operator which supports these flags. See LangRef.html for the meaning of
   /// these flags.

include/llvm/IR/Operator.h

@@ -172,12 +172,15 @@ private:
   FastMathFlags(unsigned F) : Flags(F) { }
 
 public:
+  /// This is how the bits are used in Value::SubclassOptionalData so they
+  /// should fit there too.
   enum {
     UnsafeAlgebra   = (1 << 0),
     NoNaNs          = (1 << 1),
     NoInfs          = (1 << 2),
     NoSignedZeros   = (1 << 3),
-    AllowReciprocal = (1 << 4)
+    AllowReciprocal = (1 << 4),
+    AllowContract   = (1 << 5)
   };
 
   FastMathFlags() = default;
@@ -193,6 +196,7 @@ public:
   bool noInfs() const          { return 0 != (Flags & NoInfs); }
   bool noSignedZeros() const   { return 0 != (Flags & NoSignedZeros); }
   bool allowReciprocal() const { return 0 != (Flags & AllowReciprocal); }
+  bool allowContract() const { return 0 != (Flags & AllowContract); }
   bool unsafeAlgebra() const   { return 0 != (Flags & UnsafeAlgebra); }
 
   /// Flag setters
@@ -200,12 +204,16 @@ public:
   void setNoInfs()          { Flags |= NoInfs; }
   void setNoSignedZeros()   { Flags |= NoSignedZeros; }
   void setAllowReciprocal() { Flags |= AllowReciprocal; }
+  void setAllowContract(bool B) {
+    Flags = (Flags & ~AllowContract) | B * AllowContract;
+  }
   void setUnsafeAlgebra() {
     Flags |= UnsafeAlgebra;
     setNoNaNs();
     setNoInfs();
     setNoSignedZeros();
     setAllowReciprocal();
+    setAllowContract(true);
   }
 
   void operator&=(const FastMathFlags &OtherFlags) {
@@ -257,6 +265,12 @@ private:
       (B * FastMathFlags::AllowReciprocal);
   }
 
+  void setHasAllowContract(bool B) {
+    SubclassOptionalData =
+        (SubclassOptionalData & ~FastMathFlags::AllowContract) |
+        (B * FastMathFlags::AllowContract);
+  }
+
   /// Convenience function for setting multiple fast-math flags.
   /// FMF is a mask of the bits to set.
   void setFastMathFlags(FastMathFlags FMF) {
@@ -300,6 +314,12 @@ public:
     return (SubclassOptionalData & FastMathFlags::AllowReciprocal) != 0;
   }
 
+  /// Test whether this operation is permitted to
+  /// be floating-point contracted.
+  bool hasAllowContract() const {
+    return (SubclassOptionalData & FastMathFlags::AllowContract) != 0;
+  }
+
   /// Convenience function for getting all the fast-math flags
   FastMathFlags getFastMathFlags() const {
     return FastMathFlags(SubclassOptionalData);

lib/AsmParser/LLLexer.cpp

@@ -548,6 +548,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(ninf);
   KEYWORD(nsz);
   KEYWORD(arcp);
+  KEYWORD(contract);
   KEYWORD(fast);
   KEYWORD(nuw);
   KEYWORD(nsw);

lib/AsmParser/LLParser.h

@@ -193,6 +193,10 @@ namespace llvm {
         case lltok::kw_ninf: FMF.setNoInfs();          Lex.Lex(); continue;
         case lltok::kw_nsz:  FMF.setNoSignedZeros();   Lex.Lex(); continue;
         case lltok::kw_arcp: FMF.setAllowReciprocal(); Lex.Lex(); continue;
+        case lltok::kw_contract:
+          FMF.setAllowContract(true);
+          Lex.Lex();
+          continue;
         default: return FMF;
         }
       return FMF;

lib/AsmParser/LLToken.h

@@ -98,6 +98,7 @@ enum Kind {
   kw_ninf,
   kw_nsz,
   kw_arcp,
+  kw_contract,
   kw_fast,
   kw_nuw,
   kw_nsw,

lib/Bitcode/Reader/BitcodeReader.cpp

@@ -971,6 +971,8 @@ static FastMathFlags getDecodedFastMathFlags(unsigned Val) {
     FMF.setNoSignedZeros();
   if (0 != (Val & FastMathFlags::AllowReciprocal))
     FMF.setAllowReciprocal();
+  if (0 != (Val & FastMathFlags::AllowContract))
+    FMF.setAllowContract(true);
   return FMF;
 }
 

lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -1336,6 +1336,8 @@ static uint64_t getOptimizationFlags(const Value *V) {
       Flags |= FastMathFlags::NoSignedZeros;
     if (FPMO->hasAllowReciprocal())
       Flags |= FastMathFlags::AllowReciprocal;
+    if (FPMO->hasAllowContract())
+      Flags |= FastMathFlags::AllowContract;
   }
 
   return Flags;

lib/IR/AsmWriter.cpp

@@ -1073,6 +1073,8 @@ static void WriteOptimizationInfo(raw_ostream &Out, const User *U) {
         Out << " nsz";
       if (FPO->hasAllowReciprocal())
         Out << " arcp";
+      if (FPO->hasAllowContract())
+        Out << " contract";
     }
   }
 

lib/IR/Instruction.cpp

@@ -204,6 +204,11 @@ bool Instruction::hasAllowReciprocal() const {
   return cast<FPMathOperator>(this)->hasAllowReciprocal();
 }
 
+bool Instruction::hasAllowContract() const {
+  assert(isa<FPMathOperator>(this) && "getting fast-math flag on invalid op");
+  return cast<FPMathOperator>(this)->hasAllowContract();
+}
+
 FastMathFlags Instruction::getFastMathFlags() const {
   assert(isa<FPMathOperator>(this) && "getting fast-math flag on invalid op");
   return cast<FPMathOperator>(this)->getFastMathFlags();

test/Assembler/fast-math-flags.ll

@@ -74,6 +74,18 @@ entry:
   ret float %e
 }
 
+; CHECK: @contract(
+define float @contract(float %x, float %y) {
+entry:
+; CHECK: %a = fsub contract float %x, %y
+  %a = fsub contract float %x, %y
+; CHECK: %b = fadd contract float %x, %y
+  %b = fadd contract float %x, %y
+; CHECK: %c = fmul contract float %a, %b
+  %c = fmul contract float %a, %b
+  ret float %c
+}
+
 ; CHECK: no_nan_inf
 define float @no_nan_inf(float %x, float %y) {
 entry:

test/Bitcode/compatibility.ll

@@ -760,6 +760,8 @@ define void @fastmathflags(float %op1, float %op2) {
   ; CHECK: %f.nsz = fadd nsz float %op1, %op2
   %f.arcp = fadd arcp float %op1, %op2
   ; CHECK: %f.arcp = fadd arcp float %op1, %op2
+  %f.contract = fadd contract float %op1, %op2
+  ; CHECK: %f.contract = fadd contract float %op1, %op2
   %f.fast = fadd fast float %op1, %op2
   ; CHECK: %f.fast = fadd fast float %op1, %op2
   ret void

unittests/IR/IRBuilderTest.cpp

@@ -207,7 +207,26 @@ TEST_F(IRBuilderTest, FastMathFlags) {
   EXPECT_TRUE(FCmp->hasAllowReciprocal());
 
   Builder.clearFastMathFlags();
- 
+
+  // Test FP-contract
+  FC = Builder.CreateFAdd(F, F);
+  ASSERT_TRUE(isa<Instruction>(FC));
+  FAdd = cast<Instruction>(FC);
+  EXPECT_FALSE(FAdd->hasAllowContract());
+
+  FMF.clear();
+  FMF.setAllowContract(true);
+  Builder.setFastMathFlags(FMF);
+
+  FC = Builder.CreateFAdd(F, F);
+  EXPECT_TRUE(Builder.getFastMathFlags().any());
+  EXPECT_TRUE(Builder.getFastMathFlags().AllowContract);
+  ASSERT_TRUE(isa<Instruction>(FC));
+  FAdd = cast<Instruction>(FC);
+  EXPECT_TRUE(FAdd->hasAllowContract());
+
+  Builder.clearFastMathFlags();
+
   // Test a call with FMF.
   auto CalleeTy = FunctionType::get(Type::getFloatTy(Ctx),
                                     /*isVarArg=*/false);