[clang] [llvm] [X86] EmitX86BuiltinExpr - attempt to convert SSE41/AVX1 roundps/d/ss/sd builtins to regular rounding modes (PR #171227)

[Gergo Stomfai via llvm-commits]

================
@@ -75,6 +75,52 @@ static Value *getMaskVecValue(CodeGenFunction &CGF, Value *Mask,
   return MaskVec;
 }
 
+// Emit rounding for the value X according to the rounding RoundingControl.
+static Value *emitX86Round(CodeGenFunction &CGF, Value *X,
+                           unsigned RoundingControl) {
+  unsigned RoundingMask = 0b11;
+  unsigned UseMXCSRBit = 0b1000;
+
+  unsigned RoundingMode = RoundingControl & RoundingMask;
+  bool UseMXCSR = RoundingControl & UseMXCSRBit;
+
+  Intrinsic::ID ID = Intrinsic::not_intrinsic;
+  LLVMContext &Ctx = CGF.CGM.getLLVMContext();
+
+  if (UseMXCSR) {
----------------
stomfaig wrote:

Just to clarify:
- In FPConstrained mode:
  - if MXCSR set: use `dynamic`
  - if MXCSR not set: use `constraint.floor/ceil/etc.`
 - if FPConstrained not set: Ignore MXCSR bit, and return `floor/etc.` based on the immediate value?

https://github.com/llvm/llvm-project/pull/171227