[llvm] [GlobalIsel] Combine trunc of binop (PR #107721)

[Thorsten Schütt via llvm-commits]

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@@ -1867,6 +1867,33 @@ class buildvector_of_opcode<Instruction castOpcode> : GICombineRule <
 
 def buildvector_of_truncate : buildvector_of_opcode<G_TRUNC>;
 
+// narrow binop.
+// trunc (binop X, C) --> binop (trunc X, trunc C)
+class narrow_binop_opcode<Instruction binopOpcode> : GICombineRule <
+  (defs root:$root, build_fn_matchinfo:$matchinfo),
+  (match (G_CONSTANT $const, $imm),
+         (binopOpcode $binop, $x, $const):$Binop,
+         (G_TRUNC $root, $binop):$Trunc,
+         [{ return Helper.matchNarrowBinop(*${Trunc}, *${Binop}, ${matchinfo}); }]),
+  (apply [{ Helper.applyBuildFn(*${Trunc}, ${matchinfo}); }])>;
+
+def narrow_binop_add : narrow_binop_opcode<G_ADD>;
+def narrow_binop_sub : narrow_binop_opcode<G_SUB>;
+def narrow_binop_mul : narrow_binop_opcode<G_MUL>;
+def narrow_binop_and : narrow_binop_opcode<G_AND>;
+def narrow_binop_or  : narrow_binop_opcode<G_OR>;
+def narrow_binop_xor : narrow_binop_opcode<G_XOR>;
+
+// Cast of integer.
+class integer_of_opcode<Instruction castOpcode> : GICombineRule <
+  (defs root:$root, apint_matchinfo:$matchinfo),
+  (match (G_CONSTANT $int, $imm),
+         (castOpcode $root, $int):$Cast,
+         [{ return Helper.matchCastOfInteger(*${Cast}, ${matchinfo}); }]),
+  (apply [{ Helper.replaceInstWithConstant(*${Cast}, ${matchinfo}); }])>;
+
+def integer_of_truncate : integer_of_opcode<G_TRUNC>;
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tschuett wrote:

The artefact combiner should not be touched. If this combine runs after the legalizer, the trunc(constant) would not hit anymore. There are no exts in this combine, we can only fold trunc(constant) in this PR.

https://github.com/llvm/llvm-project/pull/107721