[llvm] [GlobalISel][TableGen] Take first result for multi-output instructions (PR #81130)

[Pierre van Houtryve via llvm-commits]

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@@ -84,3 +86,34 @@ def : Pat<(two_in GPR32:$i1, GPR32:$i2), (TWO_INS GPR32:$i2, GPR32:$i1)>;
 // CHECK-NEXT: GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/2, // i1
 // CHECK-NEXT: GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT: GIR_EraseFromParent, /*InsnID*/0,
+
+//-----------------------------------------------------------------------------
+// Test where implicit defs are added using Defs.
+
+let Defs = [R0] in
+def ImplicitDefInstr : I<(outs GPR32:$dst), (ins GPR32:$src), []>;
+def OtherInstr : I<(outs GPR32:$dst), (ins GPR32:$src), []>;
+
+def : Pat<(i32 (add i32:$src, i32:$src)),
+  (OtherInstr (ImplicitDefInstr GPR32:$src))>;
+
+// CHECK: GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_ADD,
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Pierre-vh wrote:

this will definitely fail because we now use variable-length encodings (`GIMT_Encode` macros)

https://github.com/llvm/llvm-project/pull/81130