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

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);
+}