Add intrinsics for constrained floating point operations

This commit introduces a set of experimental intrinsics intended to prevent
optimizations that make assumptions about the rounding mode and floating point
exception behavior.  These intrinsics will later be extended to specify
flush-to-zero behavior.  More work is also required to model instruction
dependencies in machine code and to generate these instructions from clang
(when required by pragmas and/or command line options that are not currently
supported).

Differential Revision: https://reviews.llvm.org/D27028

llvm-svn: 293226

2 files changed, 50 insertions, 0 deletions

diff --git a/llvm/lib/IR/IntrinsicInst.cpp b/llvm/lib/IR/IntrinsicInst.cpp
index 240250662ae..c9814a96bea 100644
--- a/llvm/lib/IR/IntrinsicInst.cpp
+++ b/llvm/lib/IR/IntrinsicInst.cpp
@@ -21,6 +21,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/GlobalVariable.h"
@@ -93,3 +94,34 @@ Value *InstrProfIncrementInst::getStep() const {
   LLVMContext &Context = M->getContext();
   return ConstantInt::get(Type::getInt64Ty(Context), 1);
 }
+
+ConstrainedFPIntrinsic::RoundingMode
+ConstrainedFPIntrinsic::getRoundingMode() const {
+  Metadata *MD = dyn_cast<MetadataAsValue>(getOperand(2))->getMetadata();
+  if (!MD || !isa<MDString>(MD))
+    return rmInvalid;
+  StringRef RoundingArg = cast<MDString>(MD)->getString();
+
+  // For dynamic rounding mode, we use round to nearest but we will set the
+  // 'exact' SDNodeFlag so that the value will not be rounded.
+  return StringSwitch<RoundingMode>(RoundingArg)
+    .Case("round.dynamic",    rmDynamic)
+    .Case("round.tonearest",  rmToNearest)
+    .Case("round.downward",   rmDownward)
+    .Case("round.upward",     rmUpward)
+    .Case("round.towardzero", rmTowardZero)
+    .Default(rmInvalid);
+}
+
+ConstrainedFPIntrinsic::ExceptionBehavior
+ConstrainedFPIntrinsic::getExceptionBehavior() const {
+  Metadata *MD = dyn_cast<MetadataAsValue>(getOperand(3))->getMetadata();
+  if (!MD || !isa<MDString>(MD))
+    return ebInvalid;
+  StringRef ExceptionArg = cast<MDString>(MD)->getString();
+  return StringSwitch<ExceptionBehavior>(ExceptionArg)
+    .Case("fpexcept.ignore",  ebIgnore)
+    .Case("fpexcept.maytrap", ebMayTrap)
+    .Case("fpexcept.strict",  ebStrict)
+    .Default(ebInvalid);
+}
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 5855059a189..41593af000c 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -457,6 +457,7 @@ private:
   void visitUserOp1(Instruction &I);
   void visitUserOp2(Instruction &I) { visitUserOp1(I); }
   void visitIntrinsicCallSite(Intrinsic::ID ID, CallSite CS);
+  void visitConstrainedFPIntrinsic(ConstrainedFPIntrinsic &FPI);
   template <class DbgIntrinsicTy>
   void visitDbgIntrinsic(StringRef Kind, DbgIntrinsicTy &DII);
   void visitAtomicCmpXchgInst(AtomicCmpXchgInst &CXI);
@@ -3929,6 +3930,14 @@ void Verifier::visitIntrinsicCallSite(Intrinsic::ID ID, CallSite CS) {
            "constant int",
            CS);
     break;
+  case Intrinsic::experimental_constrained_fadd:
+  case Intrinsic::experimental_constrained_fsub:
+  case Intrinsic::experimental_constrained_fmul:
+  case Intrinsic::experimental_constrained_fdiv:
+  case Intrinsic::experimental_constrained_frem:
+    visitConstrainedFPIntrinsic(
+        cast<ConstrainedFPIntrinsic>(*CS.getInstruction()));
+    break;
   case Intrinsic::dbg_declare: // llvm.dbg.declare
     Assert(isa<MetadataAsValue>(CS.getArgOperand(0)),
            "invalid llvm.dbg.declare intrinsic call 1", CS);
@@ -4294,6 +4303,15 @@ static DISubprogram *getSubprogram(Metadata *LocalScope) {
   return nullptr;
 }
 
+void Verifier::visitConstrainedFPIntrinsic(ConstrainedFPIntrinsic &FPI) {
+  Assert(isa<MetadataAsValue>(FPI.getOperand(2)),
+         "invalid rounding mode argument", &FPI);
+  Assert(FPI.getRoundingMode() != ConstrainedFPIntrinsic::rmInvalid,
+         "invalid rounding mode argument", &FPI);
+  Assert(FPI.getExceptionBehavior() != ConstrainedFPIntrinsic::ebInvalid,
+         "invalid exception behavior argument", &FPI);
+}
+
 template <class DbgIntrinsicTy>
 void Verifier::visitDbgIntrinsic(StringRef Kind, DbgIntrinsicTy &DII) {
   auto *MD = cast<MetadataAsValue>(DII.getArgOperand(0))->getMetadata();