[X86] Add custom operation actions for f16: FABS, FNEG, and FCOPYSIGN

[StarOne01]

This pull request adds custom handling for several floating-point operations for the f16 type with respect to (#126892)..

Fixes #126892

[llvmbot]

@llvm/pr-subscribers-backend-x86

Author: Prashanth (StarOne01)

Changes

This pull request adds custom handling for several floating-point operations for the f16 type with respect to (#126892)..

---

Full diff: https://github.com/llvm/llvm-project/pull/128877.diff

1 Files Affected:

• (modified) llvm/lib/Target/X86/X86ISelLowering.cpp (+3)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index a4357197e2843..5a80754e7a3bb 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -701,6 +701,9 @@ X86TargetLowering::X86TargetLowering(const X86TargetMachine &TM,
     setOperationAction(ISD::FSUB, MVT::f16, Promote);
     setOperationAction(ISD::FMUL, MVT::f16, Promote);
     setOperationAction(ISD::FDIV, MVT::f16, Promote);
+    setOperationAction(ISD::FABS, MVT::f16, Custom);
+    setOperationAction(ISD::FNEG, MVT::f16, Custom);
+    setOperationAction(ISD::FCOPYSIGN, MVT::f16, Custom);
     setOperationAction(ISD::FP_ROUND, MVT::f16, Custom);
     setOperationAction(ISD::FP_EXTEND, MVT::f32, Custom);
     setOperationAction(ISD::FP_EXTEND, MVT::f64, Custom);

[RKSimon]

You need to runninja check-llvm-codegen-x86 and update any of the test files that have changed, you should be able to use the llvm-project\llvm\utils\update_llc_test_checks.py script

[StarOne01]

Just out of curiosity, what happened when i change the default (Promote) to Custom? i understand we override the default, making a custom lowering, that means we already have a implementation of custom lowering somewhere?

[RKSimon]

Just out of curiosity, what happened when i change the default (Promote) to Custom? i understand we override the default, making a custom lowering, that means we already have a implementation of custom lowering somewhere?

Yes, it needs to be set as Custom for a target's LowerOperation to be called, otherwise it will go through the generic legalization routes - take a look at SelectionDAGLegalize::LegalizeOp and how it selects the lower based on the Action.

[phoebewang]

LGTM.

[RKSimon]

LGTM - cheers