[FPEnv] Use single enum to represent rounding mode

Now compiler defines 5 sets of constants to represent rounding mode.
These are:

1. `llvm::APFloatBase::roundingMode`. It specifies all 5 rounding modes
defined by IEEE-754 and is used in `APFloat` implementation.

2. `clang::LangOptions::FPRoundingModeKind`. It specifies 4 of 5 IEEE-754
rounding modes and a special value for dynamic rounding mode. It is used
in clang frontend.

3. `llvm::fp::RoundingMode`. Defines the same values as
`clang::LangOptions::FPRoundingModeKind` but in different order. It is
used to specify rounding mode in in IR and functions that operate IR.

4. Rounding mode representation used by `FLT_ROUNDS` (C11, 5.2.4.2.2p7).
Besides constants for rounding mode it also uses a special value to
indicate error. It is convenient to use in intrinsic functions, as it
represents platform-independent representation for rounding mode. In this
role it is used in some pending patches.

5. Values like `FE_DOWNWARD` and other, which specify rounding mode in
library calls `fesetround` and `fegetround`. Often they represent bits
of some control register, so they are target-dependent. The same names
(not values) and a special name `FE_DYNAMIC` are used in
`#pragma STDC FENV_ROUND`.

The first 4 sets of constants are target independent and could have the
same numerical representation. It would simplify conversion between the
representations. Also now `clang::LangOptions::FPRoundingModeKind` and
`llvm::fp::RoundingMode` do not contain the value for IEEE-754 rounding
direction `roundTiesToAway`, although it is supported natively on
some targets.

This change defines all the rounding mode type via one `llvm::RoundingMode`,
which also contains rounding mode for IEEE rounding direction `roundTiesToAway`.

Differential Revision: https://reviews.llvm.org/D77379

1 files changed, 3 insertions, 19 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index b01a5a4..05bf70e 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -115,21 +115,6 @@ CodeGenFunction::~CodeGenFunction() {
     OMPBuilder->finalize();
 }
 
-// Map the LangOption for rounding mode into
-// the corresponding enum in the IR.
-static llvm::fp::RoundingMode ToConstrainedRoundingMD(
-  LangOptions::FPRoundingModeKind Kind) {
-
-  switch (Kind) {
-  case LangOptions::FPR_ToNearest:  return llvm::fp::rmToNearest;
-  case LangOptions::FPR_Downward:   return llvm::fp::rmDownward;
-  case LangOptions::FPR_Upward:     return llvm::fp::rmUpward;
-  case LangOptions::FPR_TowardZero: return llvm::fp::rmTowardZero;
-  case LangOptions::FPR_Dynamic:    return llvm::fp::rmDynamic;
-  }
-  llvm_unreachable("Unsupported FP RoundingMode");
-}
-
 // Map the LangOption for exception behavior into
 // the corresponding enum in the IR.
 static llvm::fp::ExceptionBehavior ToConstrainedExceptMD(
@@ -144,18 +129,17 @@ static llvm::fp::ExceptionBehavior ToConstrainedExceptMD(
 }
 
 void CodeGenFunction::SetFPModel() {
-  auto fpRoundingMode = ToConstrainedRoundingMD(
-                          getLangOpts().getFPRoundingMode());
+  llvm::RoundingMode RM = getLangOpts().getFPRoundingMode();
   auto fpExceptionBehavior = ToConstrainedExceptMD(
                                getLangOpts().getFPExceptionMode());
 
   if (fpExceptionBehavior == llvm::fp::ebIgnore &&
-      fpRoundingMode == llvm::fp::rmToNearest)
+      RM == llvm::RoundingMode::NearestTiesToEven)
     // Constrained intrinsics are not used.
     ;
   else {
     Builder.setIsFPConstrained(true);
-    Builder.setDefaultConstrainedRounding(fpRoundingMode);
+    Builder.setDefaultConstrainedRounding(RM);
     Builder.setDefaultConstrainedExcept(fpExceptionBehavior);
   }
 }