[WebAssembly][ConstantFolding] Fold fp-to-int truncation intrinsics

Constant fold both the trapping and saturating versions of the
WebAssembly truncation intrinsics. The tests are adapted from the
WebAssembly spec tests for the corresponding instructions.

Requested in PR46982.

Differential Revision: https://reviews.llvm.org/D85392

1 files changed, 42 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 28a30090..aaab600 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -18,6 +18,7 @@
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APInt.h"
+#include "llvm/ADT/APSInt.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/STLExtras.h"
@@ -42,6 +43,7 @@
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/IntrinsicsAMDGPU.h"
 #include "llvm/IR/IntrinsicsARM.h"
+#include "llvm/IR/IntrinsicsWebAssembly.h"
 #include "llvm/IR/IntrinsicsX86.h"
 #include "llvm/IR/Operator.h"
 #include "llvm/IR/Type.h"
@@ -1469,6 +1471,11 @@ bool llvm::canConstantFoldCallTo(const CallBase *Call, const Function *F) {
   case Intrinsic::arm_mve_vctp16:
   case Intrinsic::arm_mve_vctp32:
   case Intrinsic::arm_mve_vctp64:
+  // WebAssembly float semantics are always known
+  case Intrinsic::wasm_trunc_signed:
+  case Intrinsic::wasm_trunc_unsigned:
+  case Intrinsic::wasm_trunc_saturate_signed:
+  case Intrinsic::wasm_trunc_saturate_unsigned:
     return true;
 
   // Floating point operations cannot be folded in strictfp functions in
@@ -1861,11 +1868,45 @@ static Constant *ConstantFoldScalarCall1(StringRef Name,
       return ConstantInt::get(Ty->getContext(), Val.bitcastToAPInt());
     }
 
+    APFloat U = Op->getValueAPF();
+
+    if (IntrinsicID == Intrinsic::wasm_trunc_signed ||
+        IntrinsicID == Intrinsic::wasm_trunc_unsigned ||
+        IntrinsicID == Intrinsic::wasm_trunc_saturate_signed ||
+        IntrinsicID == Intrinsic::wasm_trunc_saturate_unsigned) {
+
+      bool Saturating = IntrinsicID == Intrinsic::wasm_trunc_saturate_signed ||
+                        IntrinsicID == Intrinsic::wasm_trunc_saturate_unsigned;
+      bool Signed = IntrinsicID == Intrinsic::wasm_trunc_signed ||
+                    IntrinsicID == Intrinsic::wasm_trunc_saturate_signed;
+
+      if (U.isNaN())
+        return Saturating ? ConstantInt::get(Ty, 0) : nullptr;
+
+      unsigned Width = Ty->getIntegerBitWidth();
+      APSInt Int(Width, !Signed);
+      bool IsExact = false;
+      APFloat::opStatus Status =
+          U.convertToInteger(Int, APFloat::rmTowardZero, &IsExact);
+
+      if (Status == APFloat::opOK || Status == APFloat::opInexact)
+        return ConstantInt::get(Ty, Int);
+
+      if (!Saturating)
+        return nullptr;
+
+      if (U.isNegative())
+        return Signed ? ConstantInt::get(Ty, APInt::getSignedMinValue(Width))
+                      : ConstantInt::get(Ty, APInt::getMinValue(Width));
+      else
+        return Signed ? ConstantInt::get(Ty, APInt::getSignedMaxValue(Width))
+                      : ConstantInt::get(Ty, APInt::getMaxValue(Width));
+    }
+
     if (!Ty->isHalfTy() && !Ty->isFloatTy() && !Ty->isDoubleTy())
       return nullptr;
 
     // Use internal versions of these intrinsics.
-    APFloat U = Op->getValueAPF();
 
     if (IntrinsicID == Intrinsic::nearbyint || IntrinsicID == Intrinsic::rint) {
       U.roundToIntegral(APFloat::rmNearestTiesToEven);