[IR] Add `llvm.modf` intrinsic (#121948)

This adds the `llvm.modf` intrinsic, legalization, and lowering (mostly
reusing the lowering for sincos and frexp).

The `llvm.modf` intrinsic takes a floating-point value and returns both
the integral and fractional parts (as a struct).

```
declare { float, float }             @llvm.modf.f32(float  %Val)
declare { double, double }           @llvm.modf.f64(double %Val)
declare { x86_fp80, x86_fp80 }       @llvm.modf.f80(x86_fp80  %Val)
declare { fp128, fp128 }             @llvm.modf.f128(fp128 %Val)
declare { ppc_fp128, ppc_fp128 }     @llvm.modf.ppcf128(ppc_fp128  %Val)
declare { <4 x float>, <4 x float> } @llvm.modf.v4f32(<4 x float>  %Val)
```

This corresponds to the libm `modf` function but returns multiple values
in a struct (rather than take output pointers), which makes it easier to
vectorize.

1 files changed, 8 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringBase.cpp b/llvm/lib/CodeGen/TargetLoweringBase.cpp
index 9c56912..1f39ec20 100644
--- a/llvm/lib/CodeGen/TargetLoweringBase.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringBase.cpp
@@ -407,6 +407,11 @@ RTLIB::Libcall RTLIB::getFSINCOS(EVT RetVT) {
                       SINCOS_PPCF128);
 }
 
+RTLIB::Libcall RTLIB::getMODF(EVT RetVT) {
+  return getFPLibCall(RetVT, MODF_F32, MODF_F64, MODF_F80, MODF_F128,
+                      MODF_PPCF128);
+}
+
 RTLIB::Libcall RTLIB::getOutlineAtomicHelper(const Libcall (&LC)[5][4],
                                              AtomicOrdering Order,
                                              uint64_t MemSize) {
@@ -775,9 +780,9 @@ void TargetLoweringBase::initActions() {
     setOperationAction({ISD::BITREVERSE, ISD::PARITY}, VT, Expand);
 
     // These library functions default to expand.
-    setOperationAction(
-        {ISD::FROUND, ISD::FPOWI, ISD::FLDEXP, ISD::FFREXP, ISD::FSINCOS}, VT,
-        Expand);
+    setOperationAction({ISD::FROUND, ISD::FPOWI, ISD::FLDEXP, ISD::FFREXP,
+                        ISD::FSINCOS, ISD::FMODF},
+                       VT, Expand);
 
     // These operations default to expand for vector types.
     if (VT.isVector())