llvm dev - Aug 2014 - [LLVMdev] Proposal: Add a target lowering hook to state that target supports floating point exception behavior.

Hello All,

the patch below adds a target lowering hook to state that the target supports
(or not) floating point exception behavior. The patch is small and contains one
possible use for the hook (folding potentially exception raising fp operations).

Any comments?

Thanks

Pedro

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Index: include/llvm/Target/TargetLowering.h
==================================================================---
include/llvm/Target/TargetLowering.h	(revision 215148)
+++ include/llvm/Target/TargetLowering.h	(working copy)
@@ -261,6 +261,11 @@
   bool isMaskAndBranchFoldingLegal() const {
     return MaskAndBranchFoldingIsLegal;
   }
+  
+  /// Return true if target supports floating point exceptions.
+  bool hasFloatingPointExceptions() const {
+    return FloatingPointExceptions;
+  }
 
   /// Return the ValueType of the result of SETCC operations.  Also used to
   /// obtain the target's preferred type for the condition operand of
SELECT and
@@ -1053,6 +1058,12 @@
   /// possible, should be replaced by an alternate sequence of instructions not
   /// containing an integer divide.
   void setIntDivIsCheap(bool isCheap = true) { IntDivIsCheap = isCheap; }
+  
+  /// Tells the code generator that this target supports floating point
+  /// exceptions and cares about preserving floating point exception behavior.
+  void setHasFloatingPointExceptions(bool FPExceptions = true) {
+    FloatingPointExceptions = FPExceptions;
+  }
 
   /// Tells the code generator which bitwidths to bypass.
   void addBypassSlowDiv(unsigned int SlowBitWidth, unsigned int FastBitWidth) {
Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp
==================================================================---
lib/CodeGen/SelectionDAG/SelectionDAG.cpp	(revision 215148)
+++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp	(working copy)
@@ -3402,6 +3402,7 @@
   }
 
   // Constant fold FP operations.
+  bool HasFPExceptions = TLI->hasFloatingPointExceptions();
   ConstantFPSDNode *N1CFP = dyn_cast<ConstantFPSDNode>(N1.getNode());
   ConstantFPSDNode *N2CFP = dyn_cast<ConstantFPSDNode>(N2.getNode());
   if (N1CFP) {
@@ -3415,28 +3416,32 @@
       switch (Opcode) {
       case ISD::FADD:
         s = V1.add(V2, APFloat::rmNearestTiesToEven);
-        if (s != APFloat::opInvalidOp)
+        if (!HasFPExceptions || s != APFloat::opInvalidOp)
           return getConstantFP(V1, VT);
         break;
       case ISD::FSUB:
         s = V1.subtract(V2, APFloat::rmNearestTiesToEven);
-        if (s!=APFloat::opInvalidOp)
+        if (!HasFPExceptions || s!=APFloat::opInvalidOp)
           return getConstantFP(V1, VT);
         break;
       case ISD::FMUL:
         s = V1.multiply(V2, APFloat::rmNearestTiesToEven);
-        if (s!=APFloat::opInvalidOp)
+        if (!HasFPExceptions || s!=APFloat::opInvalidOp)
           return getConstantFP(V1, VT);
         break;
       case ISD::FDIV:
         s = V1.divide(V2, APFloat::rmNearestTiesToEven);
-        if (s!=APFloat::opInvalidOp && s!=APFloat::opDivByZero)
+        if (!HasFPExceptions || (s!=APFloat::opInvalidOp &&
+                                 s!=APFloat::opDivByZero)) {
           return getConstantFP(V1, VT);
+        }
         break;
       case ISD::FREM :
         s = V1.mod(V2, APFloat::rmNearestTiesToEven);
-        if (s!=APFloat::opInvalidOp && s!=APFloat::opDivByZero)
+        if (!HasFPExceptions || (s!=APFloat::opInvalidOp &&
+                                 s!=APFloat::opDivByZero)) {
           return getConstantFP(V1, VT);
+        }
         break;
       case ISD::FCOPYSIGN:
         V1.copySign(V2);
Index: lib/CodeGen/TargetLoweringBase.cpp
==================================================================---
lib/CodeGen/TargetLoweringBase.cpp	(revision 215148)
+++ lib/CodeGen/TargetLoweringBase.cpp	(working copy)
@@ -705,6 +705,7 @@
   JumpIsExpensive = false;
   PredictableSelectIsExpensive = false;
   MaskAndBranchFoldingIsLegal = false;
+  FloatingPointExceptions = true;
   StackPointerRegisterToSaveRestore = 0;
   ExceptionPointerRegister = 0;
   ExceptionSelectorRegister = 0;

Hi Pedro,

I would rename the variable FloatingPointExceptions to
HasFloatingPointExceptions.

-Juergen

PS: Patches should go to llvm-commits

On Aug 7, 2014, at 3:07 PM, Pedro Artigas <partigas at apple.com> wrote:
> Hello All,
> 
> the patch below adds a target lowering hook to state that the target
supports (or not) floating point exception behavior. The patch is small and
contains one possible use for the hook (folding potentially exception raising fp
operations).
> 
> Any comments?
> 
> Thanks
> 
> Pedro
> 
> <opensource1.txt>
> 
> Index: include/llvm/Target/TargetLowering.h
> ==================================================================> ---
include/llvm/Target/TargetLowering.h	(revision 215148)
> +++ include/llvm/Target/TargetLowering.h	(working copy)
> @@ -261,6 +261,11 @@
>   bool isMaskAndBranchFoldingLegal() const {
>     return MaskAndBranchFoldingIsLegal;
>   }
> +  
> +  /// Return true if target supports floating point exceptions.
> +  bool hasFloatingPointExceptions() const {
> +    return FloatingPointExceptions;
> +  }
> 
>   /// Return the ValueType of the result of SETCC operations.  Also used to
>   /// obtain the target's preferred type for the condition operand of
SELECT and
> @@ -1053,6 +1058,12 @@
>   /// possible, should be replaced by an alternate sequence of instructions
not
>   /// containing an integer divide.
>   void setIntDivIsCheap(bool isCheap = true) { IntDivIsCheap = isCheap; }
> +  
> +  /// Tells the code generator that this target supports floating point
> +  /// exceptions and cares about preserving floating point exception
behavior.
> +  void setHasFloatingPointExceptions(bool FPExceptions = true) {
> +    FloatingPointExceptions = FPExceptions;
> +  }
> 
>   /// Tells the code generator which bitwidths to bypass.
>   void addBypassSlowDiv(unsigned int SlowBitWidth, unsigned int
FastBitWidth) {
> Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp
> ==================================================================> ---
lib/CodeGen/SelectionDAG/SelectionDAG.cpp	(revision 215148)
> +++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp	(working copy)
> @@ -3402,6 +3402,7 @@
>   }
> 
>   // Constant fold FP operations.
> +  bool HasFPExceptions = TLI->hasFloatingPointExceptions();
>   ConstantFPSDNode *N1CFP = dyn_cast<ConstantFPSDNode>(N1.getNode());
>   ConstantFPSDNode *N2CFP = dyn_cast<ConstantFPSDNode>(N2.getNode());
>   if (N1CFP) {
> @@ -3415,28 +3416,32 @@
>       switch (Opcode) {
>       case ISD::FADD:
>         s = V1.add(V2, APFloat::rmNearestTiesToEven);
> -        if (s != APFloat::opInvalidOp)
> +        if (!HasFPExceptions || s != APFloat::opInvalidOp)
>           return getConstantFP(V1, VT);
>         break;
>       case ISD::FSUB:
>         s = V1.subtract(V2, APFloat::rmNearestTiesToEven);
> -        if (s!=APFloat::opInvalidOp)
> +        if (!HasFPExceptions || s!=APFloat::opInvalidOp)
>           return getConstantFP(V1, VT);
>         break;
>       case ISD::FMUL:
>         s = V1.multiply(V2, APFloat::rmNearestTiesToEven);
> -        if (s!=APFloat::opInvalidOp)
> +        if (!HasFPExceptions || s!=APFloat::opInvalidOp)
>           return getConstantFP(V1, VT);
>         break;
>       case ISD::FDIV:
>         s = V1.divide(V2, APFloat::rmNearestTiesToEven);
> -        if (s!=APFloat::opInvalidOp && s!=APFloat::opDivByZero)
> +        if (!HasFPExceptions || (s!=APFloat::opInvalidOp &&
> +                                 s!=APFloat::opDivByZero)) {
>           return getConstantFP(V1, VT);
> +        }
>         break;
>       case ISD::FREM :
>         s = V1.mod(V2, APFloat::rmNearestTiesToEven);
> -        if (s!=APFloat::opInvalidOp && s!=APFloat::opDivByZero)
> +        if (!HasFPExceptions || (s!=APFloat::opInvalidOp &&
> +                                 s!=APFloat::opDivByZero)) {
>           return getConstantFP(V1, VT);
> +        }
>         break;
>       case ISD::FCOPYSIGN:
>         V1.copySign(V2);
> Index: lib/CodeGen/TargetLoweringBase.cpp
> ==================================================================> ---
lib/CodeGen/TargetLoweringBase.cpp	(revision 215148)
> +++ lib/CodeGen/TargetLoweringBase.cpp	(working copy)
> @@ -705,6 +705,7 @@
>   JumpIsExpensive = false;
>   PredictableSelectIsExpensive = false;
>   MaskAndBranchFoldingIsLegal = false;
> +  FloatingPointExceptions = true;
>   StackPointerRegisterToSaveRestore = 0;
>   ExceptionPointerRegister = 0;
>   ExceptionSelectorRegister = 0;
> 
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

There's a lot of cut and paste in those routines. Can you do something
to unify it a bit? Also, do we have any ports that have support
floating point exceptions?

-eric

On Thu, Aug 7, 2014 at 3:07 PM, Pedro Artigas <partigas at apple.com>
wrote:
> Hello All,
>
> the patch below adds a target lowering hook to state that the target
supports (or not) floating point exception behavior. The patch is small and
contains one possible use for the hook (folding potentially exception raising fp
operations).
>
> Any comments?
>
> Thanks
>
> Pedro
>
>
>
>
> Index: include/llvm/Target/TargetLowering.h
> ==================================================================> ---
include/llvm/Target/TargetLowering.h        (revision 215148)
> +++ include/llvm/Target/TargetLowering.h        (working copy)
> @@ -261,6 +261,11 @@
>    bool isMaskAndBranchFoldingLegal() const {
>      return MaskAndBranchFoldingIsLegal;
>    }
> +
> +  /// Return true if target supports floating point exceptions.
> +  bool hasFloatingPointExceptions() const {
> +    return FloatingPointExceptions;
> +  }
>
>    /// Return the ValueType of the result of SETCC operations.  Also used
to
>    /// obtain the target's preferred type for the condition operand of
SELECT and
> @@ -1053,6 +1058,12 @@
>    /// possible, should be replaced by an alternate sequence of
instructions not
>    /// containing an integer divide.
>    void setIntDivIsCheap(bool isCheap = true) { IntDivIsCheap = isCheap; }
> +
> +  /// Tells the code generator that this target supports floating point
> +  /// exceptions and cares about preserving floating point exception
behavior.
> +  void setHasFloatingPointExceptions(bool FPExceptions = true) {
> +    FloatingPointExceptions = FPExceptions;
> +  }
>
>    /// Tells the code generator which bitwidths to bypass.
>    void addBypassSlowDiv(unsigned int SlowBitWidth, unsigned int
FastBitWidth) {
> Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp
> ==================================================================> ---
lib/CodeGen/SelectionDAG/SelectionDAG.cpp   (revision 215148)
> +++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp   (working copy)
> @@ -3402,6 +3402,7 @@
>    }
>
>    // Constant fold FP operations.
> +  bool HasFPExceptions = TLI->hasFloatingPointExceptions();
>    ConstantFPSDNode *N1CFP =
dyn_cast<ConstantFPSDNode>(N1.getNode());
>    ConstantFPSDNode *N2CFP =
dyn_cast<ConstantFPSDNode>(N2.getNode());
>    if (N1CFP) {
> @@ -3415,28 +3416,32 @@
>        switch (Opcode) {
>        case ISD::FADD:
>          s = V1.add(V2, APFloat::rmNearestTiesToEven);
> -        if (s != APFloat::opInvalidOp)
> +        if (!HasFPExceptions || s != APFloat::opInvalidOp)
>            return getConstantFP(V1, VT);
>          break;
>        case ISD::FSUB:
>          s = V1.subtract(V2, APFloat::rmNearestTiesToEven);
> -        if (s!=APFloat::opInvalidOp)
> +        if (!HasFPExceptions || s!=APFloat::opInvalidOp)
>            return getConstantFP(V1, VT);
>          break;
>        case ISD::FMUL:
>          s = V1.multiply(V2, APFloat::rmNearestTiesToEven);
> -        if (s!=APFloat::opInvalidOp)
> +        if (!HasFPExceptions || s!=APFloat::opInvalidOp)
>            return getConstantFP(V1, VT);
>          break;
>        case ISD::FDIV:
>          s = V1.divide(V2, APFloat::rmNearestTiesToEven);
> -        if (s!=APFloat::opInvalidOp && s!=APFloat::opDivByZero)
> +        if (!HasFPExceptions || (s!=APFloat::opInvalidOp &&
> +                                 s!=APFloat::opDivByZero)) {
>            return getConstantFP(V1, VT);
> +        }
>          break;
>        case ISD::FREM :
>          s = V1.mod(V2, APFloat::rmNearestTiesToEven);
> -        if (s!=APFloat::opInvalidOp && s!=APFloat::opDivByZero)
> +        if (!HasFPExceptions || (s!=APFloat::opInvalidOp &&
> +                                 s!=APFloat::opDivByZero)) {
>            return getConstantFP(V1, VT);
> +        }
>          break;
>        case ISD::FCOPYSIGN:
>          V1.copySign(V2);
> Index: lib/CodeGen/TargetLoweringBase.cpp
> ==================================================================> ---
lib/CodeGen/TargetLoweringBase.cpp  (revision 215148)
> +++ lib/CodeGen/TargetLoweringBase.cpp  (working copy)
> @@ -705,6 +705,7 @@
>    JumpIsExpensive = false;
>    PredictableSelectIsExpensive = false;
>    MaskAndBranchFoldingIsLegal = false;
> +  FloatingPointExceptions = true;
>    StackPointerRegisterToSaveRestore = 0;
>    ExceptionPointerRegister = 0;
>    ExceptionSelectorRegister = 0;
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>

I assume you meant to ask for ports that *don’t* support floating point
exceptions.  To my knowledge, neither R600 nor NVPTX support floating point
exceptions.

—Owen
> On Aug 8, 2014, at 2:41 PM, Eric Christopher <echristo at gmail.com>
wrote:
> 
> There's a lot of cut and paste in those routines. Can you do something
> to unify it a bit? Also, do we have any ports that have support
> floating point exceptions?
> 
> -eric
> 
> On Thu, Aug 7, 2014 at 3:07 PM, Pedro Artigas <partigas at apple.com>
wrote:
>> Hello All,
>> 
>> the patch below adds a target lowering hook to state that the target
supports (or not) floating point exception behavior. The patch is small and
contains one possible use for the hook (folding potentially exception raising fp
operations).
>> 
>> Any comments?
>> 
>> Thanks
>> 
>> Pedro
>> 
>> 
>> 
>> 
>> Index: include/llvm/Target/TargetLowering.h
>>
==================================================================>> ---
include/llvm/Target/TargetLowering.h        (revision 215148)
>> +++ include/llvm/Target/TargetLowering.h        (working copy)
>> @@ -261,6 +261,11 @@
>>   bool isMaskAndBranchFoldingLegal() const {
>>     return MaskAndBranchFoldingIsLegal;
>>   }
>> +
>> +  /// Return true if target supports floating point exceptions.
>> +  bool hasFloatingPointExceptions() const {
>> +    return FloatingPointExceptions;
>> +  }
>> 
>>   /// Return the ValueType of the result of SETCC operations.  Also
used to
>>   /// obtain the target's preferred type for the condition operand
of SELECT and
>> @@ -1053,6 +1058,12 @@
>>   /// possible, should be replaced by an alternate sequence of
instructions not
>>   /// containing an integer divide.
>>   void setIntDivIsCheap(bool isCheap = true) { IntDivIsCheap = isCheap;
}
>> +
>> +  /// Tells the code generator that this target supports floating
point
>> +  /// exceptions and cares about preserving floating point exception
behavior.
>> +  void setHasFloatingPointExceptions(bool FPExceptions = true) {
>> +    FloatingPointExceptions = FPExceptions;
>> +  }
>> 
>>   /// Tells the code generator which bitwidths to bypass.
>>   void addBypassSlowDiv(unsigned int SlowBitWidth, unsigned int
FastBitWidth) {
>> Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp
>>
==================================================================>> ---
lib/CodeGen/SelectionDAG/SelectionDAG.cpp   (revision 215148)
>> +++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp   (working copy)
>> @@ -3402,6 +3402,7 @@
>>   }
>> 
>>   // Constant fold FP operations.
>> +  bool HasFPExceptions = TLI->hasFloatingPointExceptions();
>>   ConstantFPSDNode *N1CFP =
dyn_cast<ConstantFPSDNode>(N1.getNode());
>>   ConstantFPSDNode *N2CFP =
dyn_cast<ConstantFPSDNode>(N2.getNode());
>>   if (N1CFP) {
>> @@ -3415,28 +3416,32 @@
>>       switch (Opcode) {
>>       case ISD::FADD:
>>         s = V1.add(V2, APFloat::rmNearestTiesToEven);
>> -        if (s != APFloat::opInvalidOp)
>> +        if (!HasFPExceptions || s != APFloat::opInvalidOp)
>>           return getConstantFP(V1, VT);
>>         break;
>>       case ISD::FSUB:
>>         s = V1.subtract(V2, APFloat::rmNearestTiesToEven);
>> -        if (s!=APFloat::opInvalidOp)
>> +        if (!HasFPExceptions || s!=APFloat::opInvalidOp)
>>           return getConstantFP(V1, VT);
>>         break;
>>       case ISD::FMUL:
>>         s = V1.multiply(V2, APFloat::rmNearestTiesToEven);
>> -        if (s!=APFloat::opInvalidOp)
>> +        if (!HasFPExceptions || s!=APFloat::opInvalidOp)
>>           return getConstantFP(V1, VT);
>>         break;
>>       case ISD::FDIV:
>>         s = V1.divide(V2, APFloat::rmNearestTiesToEven);
>> -        if (s!=APFloat::opInvalidOp &&
s!=APFloat::opDivByZero)
>> +        if (!HasFPExceptions || (s!=APFloat::opInvalidOp &&
>> +                                 s!=APFloat::opDivByZero)) {
>>           return getConstantFP(V1, VT);
>> +        }
>>         break;
>>       case ISD::FREM :
>>         s = V1.mod(V2, APFloat::rmNearestTiesToEven);
>> -        if (s!=APFloat::opInvalidOp &&
s!=APFloat::opDivByZero)
>> +        if (!HasFPExceptions || (s!=APFloat::opInvalidOp &&
>> +                                 s!=APFloat::opDivByZero)) {
>>           return getConstantFP(V1, VT);
>> +        }
>>         break;
>>       case ISD::FCOPYSIGN:
>>         V1.copySign(V2);
>> Index: lib/CodeGen/TargetLoweringBase.cpp
>>
==================================================================>> ---
lib/CodeGen/TargetLoweringBase.cpp  (revision 215148)
>> +++ lib/CodeGen/TargetLoweringBase.cpp  (working copy)
>> @@ -705,6 +705,7 @@
>>   JumpIsExpensive = false;
>>   PredictableSelectIsExpensive = false;
>>   MaskAndBranchFoldingIsLegal = false;
>> +  FloatingPointExceptions = true;
>>   StackPointerRegisterToSaveRestore = 0;
>>   ExceptionPointerRegister = 0;
>>   ExceptionSelectorRegister = 0;
>> 
>> 
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>