[llvm] [AMDGPU][GISel] Add 64bit pattern to emit `v_lshl_add_u64` (PR #124763)

[Matt Arsenault via llvm-commits]

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@@ -762,15 +762,27 @@ def : ThreeOp_i32_Pats<and, or, V_AND_OR_B32_e64>;
 def : ThreeOp_i32_Pats<or, or, V_OR3_B32_e64>;
 def : ThreeOp_i32_Pats<xor, add, V_XAD_U32_e64>;
 
+let SubtargetPredicate = HasLShlAddB64 in {
+// TODO: Canonicalize these in the target specific CombinerHelper?
 def : GCNPat<
- (DivergentBinFrag<mul> i32:$src0, IsPow2Plus1:$src1),
- (V_LSHL_ADD_U32_e64 i32:$src0, (i32 (Log2_32 imm:$src1)), i32:$src0)>;
+  (ptradd (shl i64:$src0, i32:$shift), i64:$src1),
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arsenm wrote:

Does ptradd just get ignored by the DAG? Should this maintain the DivergentBinFrag predicate? 

https://github.com/llvm/llvm-project/pull/124763