[ConstantFPRange] Add support for flushDenormals (#163074)

This patch provides a helper function to handle non-IEEE denormal
flushing behaviours. For the dynamic mode, it returns a union of all
possible results.

1 files changed, 22 insertions, 0 deletions

diff --git a/llvm/lib/IR/ConstantFPRange.cpp b/llvm/lib/IR/ConstantFPRange.cpp
index 51d2e21..e9c058e 100644
--- a/llvm/lib/IR/ConstantFPRange.cpp
+++ b/llvm/lib/IR/ConstantFPRange.cpp
@@ -8,6 +8,7 @@
 
 #include "llvm/IR/ConstantFPRange.h"
 #include "llvm/ADT/APFloat.h"
+#include "llvm/ADT/FloatingPointMode.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
@@ -506,3 +507,24 @@ ConstantFPRange ConstantFPRange::sub(const ConstantFPRange &Other) const {
   // fsub X, Y = fadd X, (fneg Y)
   return add(Other.negate());
 }
+
+void ConstantFPRange::flushDenormals(DenormalMode::DenormalModeKind Mode) {
+  if (Mode == DenormalMode::IEEE)
+    return;
+  FPClassTest Class = classify();
+  if (!(Class & fcSubnormal))
+    return;
+
+  auto &Sem = getSemantics();
+  // PreserveSign: PosSubnormal -> PosZero, NegSubnormal -> NegZero
+  // PositiveZero: PosSubnormal -> PosZero, NegSubnormal -> PosZero
+  // Dynamic:      PosSubnormal -> PosZero, NegSubnormal -> NegZero/PosZero
+  bool ZeroLowerNegative =
+      Mode != DenormalMode::PositiveZero && (Class & fcNegSubnormal);
+  bool ZeroUpperNegative =
+      Mode == DenormalMode::PreserveSign && !(Class & fcPosSubnormal);
+  assert((ZeroLowerNegative || !ZeroUpperNegative) &&
+         "ZeroLower is greater than ZeroUpper.");
+  Lower = minnum(Lower, APFloat::getZero(Sem, ZeroLowerNegative));
+  Upper = maxnum(Upper, APFloat::getZero(Sem, ZeroUpperNegative));
+}