[llvm] AMDGPU: Support llvm.exp10 (PR #65860)

[Pierre van Houtryve via llvm-commits]

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@@ -2827,12 +2830,59 @@ SDValue AMDGPUTargetLowering::lowerFEXPUnsafe(SDValue X, const SDLoc &SL,
                      Flags);
 }
 
+SDValue AMDGPUTargetLowering::lowerFEXP10Unsafe(SDValue X, const SDLoc &SL,
+                                                SelectionDAG &DAG,
+                                                SDNodeFlags Flags) const {
+  const EVT VT = X.getValueType();
+  const unsigned Exp2Op = VT == MVT::f32 ? AMDGPUISD::EXP : ISD::FEXP2;
+
+  if (VT != MVT::f32 || !needsDenormHandlingF32(DAG, X, Flags)) {
+    // exp2(x * 0x1.a92000p+1f) * exp2(x * 0x1.4f0978p-11f);
+    SDValue K0 = DAG.getConstantFP(0x1.a92000p+1f, SL, VT);
+    SDValue K1 = DAG.getConstantFP(0x1.4f0978p-11f, SL, VT);
+
+
+    SDValue Mul0 = DAG.getNode(ISD::FMUL, SL, VT, X, K0, Flags);
+    SDValue Exp2_0 = DAG.getNode(Exp2Op, SL, VT, Mul0, Flags);
+    SDValue Mul1 = DAG.getNode(ISD::FMUL, SL, VT, X, K1, Flags);
+    SDValue Exp2_1 = DAG.getNode(Exp2Op, SL, VT, Mul1, Flags);
+    return DAG.getNode(ISD::FMUL, SL, VT, Exp2_0, Exp2_1);
+  }
+
----------------
Pierre-vh wrote:

Can you add a comment like the one in the `VT != MVT::f32` case to show what the math is?

https://github.com/llvm/llvm-project/pull/65860