[llvm] AMDGPU: Avoid instantiating PatFrag with null_frag (PR #77271)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/77271

This makes it possible to pass null_frag to the MAIInst multiclass.

null_frag does not work as you may hope if used as the input to a PatFrag, which is what happens when it's passed through to *MAIFrag. Avoid this by checking for null_frag. It might be possible to hack up tablegen to allow consuming PatFrag inputs.

>From 6bfb80835b8e2a7d34b394cfe66a91bdb2b421e0 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Mon, 8 Jan 2024 11:55:45 +0700
Subject: [PATCH] AMDGPU: Avoid instantiating PatFrag with null_frag

This makes it possible to pass null_frag to the MAIInst
multiclass.

null_frag does not work as you may hope if used as the input
to a PatFrag, which is what happens when it's passed through to
*MAIFrag. Avoid this by checking for null_frag. It might be
possible to hack up tablegen to allow consuming PatFrag inputs.
---
 llvm/lib/Target/AMDGPU/VOP3PInstructions.td | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Target/AMDGPU/VOP3PInstructions.td b/llvm/lib/Target/AMDGPU/VOP3PInstructions.td
index 985b77be1d881e..e9d6f67aee1644 100644
--- a/llvm/lib/Target/AMDGPU/VOP3PInstructions.td
+++ b/llvm/lib/Target/AMDGPU/VOP3PInstructions.td
@@ -623,12 +623,12 @@ multiclass MAIInst<string OpName, string P, SDPatternOperator node,
     // FP32 denorm mode is respected, rounding mode is not. Exceptions are not supported.
     let Constraints = !if(NoDstOverlap, "@earlyclobber $vdst", "") in {
       def _e64 : MAIInst<OpName, !cast<VOPProfileMAI>("VOPProfileMAI_" # P),
-                         !if(NoDstOverlap, null_frag, AgprMAIFrag<node>)>,
+                         !if(!or(NoDstOverlap, !eq(node, null_frag)), null_frag, AgprMAIFrag<node>)>,
                  MFMATable<0, NAME # "_e64">;
 
       let SubtargetPredicate = isGFX90APlus, Mnemonic = OpName in
       def _vgprcd_e64 : MAIInst<OpName # "_vgprcd", !cast<VOPProfileMAI>("VOPProfileMAI_" # P # "_VCD"),
-                                !if(NoDstOverlap, null_frag, VgprMAIFrag<node>)>,
+                                !if(!or(NoDstOverlap, !eq(node, null_frag)), null_frag, VgprMAIFrag<node>)>,
                         MFMATable<0, NAME # "_vgprcd_e64">;
     }
 
@@ -636,12 +636,13 @@ multiclass MAIInst<string OpName, string P, SDPatternOperator node,
       let Constraints = !if(NoDstOverlap, "$vdst = $src2", ""),
           isConvertibleToThreeAddress = NoDstOverlap,
           Mnemonic = OpName in {
-        def "_mac_e64" : MAIInst<OpName # "_mac", !cast<VOPProfileMAI>("VOPProfileMAI_" # P), AgprMAIFrag<node>>,
+        def "_mac_e64" : MAIInst<OpName # "_mac", !cast<VOPProfileMAI>("VOPProfileMAI_" # P),
+                                 !if(!eq(node, null_frag), null_frag, AgprMAIFrag<node>)>,
                          MFMATable<1, NAME # "_e64">;
 
         let SubtargetPredicate = isGFX90APlus in
         def _mac_vgprcd_e64 : MAIInst<OpName # "_mac_vgprcd", !cast<VOPProfileMAI>("VOPProfileMAI_" # P # "_VCD"),
-                                      VgprMAIFrag<node>>,
+                                      !if(!eq(node, null_frag), null_frag, VgprMAIFrag<node>)>,
                               MFMATable<1, NAME # "_vgprcd_e64">;
       }
     }