[llvm] [AMDGPU] Fix canonicalization of truncated values. (PR #83054)

[Harald van Dijk via llvm-commits]

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@@ -2944,6 +2944,34 @@ def : GCNPat<
    (V_BFREV_B32_e64 (i32 (EXTRACT_SUBREG VReg_64:$a, sub1))), sub0,
    (V_BFREV_B32_e64 (i32 (EXTRACT_SUBREG VReg_64:$a, sub0))), sub1)>;
 
+// If fcanonicalize's operand is implicitly canonicalized, we only need a copy.
+let AddedComplexity = 1000 in {
+def : GCNPat<
+  (is_canonicalized_1<fcanonicalize> f16:$src),
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hvdijk wrote:

Not a dumb question, one that I would like an answer to as well :) Variations of that were what I tried first, but I couldn't get it to work, and TableGen's error messages were not helpful in letting me figure out a way to get it working. I decided to just stick what was already being done.

https://github.com/llvm/llvm-project/pull/83054