[llvm] true16 codegen madmixpat (PR #124995)

[Brox Chen via llvm-commits]

https://github.com/broxigarchen updated https://github.com/llvm/llvm-project/pull/124995

>From dbe9b2909f674e9a8b81f06beed2245c541fc988 Mon Sep 17 00:00:00 2001
From: guochen2 <guochen2 at amd.com>
Date: Wed, 29 Jan 2025 17:20:01 -0500
Subject: [PATCH] madmixpat update for true16

---
 llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp        | 4 ++++
 llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp | 9 +++++++++
 2 files changed, 13 insertions(+)

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp b/llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
index 8e90754103ff1..3f51829d7600b 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
@@ -3651,6 +3651,10 @@ bool AMDGPUDAGToDAGISel::SelectVOP3PMadMixModsImpl(SDValue In, SDValue &Src,
       // TODO: Should we try to look for neg/abs here?
     }
 
+    // Prevent unnecessary subreg COPY to VGPR_16
+    if (Subtarget->UseRealTrue16Insts() && Src.getOpcode() == ISD::TRUNCATE) {
+      Src = Src.getOperand(0);
+    }
     return true;
   }
 
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp b/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
index a787c10a9421c..38f63e9fe50d7 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
@@ -5841,6 +5841,15 @@ AMDGPUInstructionSelector::selectVOP3PMadMixModsImpl(MachineOperand &Root,
       CheckAbsNeg();
     }
 
+    // Since we looked through FPEXT and removed it, we must also remove
+    // G_TRUNC. G_TRUNC to 16-bits would have a destination in RC VGPR_16, which
+    // is not compatible with MadMix instructions
+    if (Subtarget->UseRealTrue16Insts() && MI->getOpcode() == AMDGPU::G_TRUNC) {
+      MO = &MI->getOperand(1);
+      Src = MO->getReg();
+      MI = getDefIgnoringCopies(Src, *MRI);
+    }
+
     Matched = true;
   }