[llvm] [X86] Fold some (truncate (srl (add X, C1), C2)) patterns to (add (truncate (srl X, C2), C1')) (PR #126448)

[Phoebe Wang via llvm-commits]

=?utf-8?q?João?= Gouveia <jtalonegouveia at gmail.com>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/126448 at github.com>


================
@@ -48472,6 +48472,64 @@ static SDValue combineSetCCMOVMSK(SDValue EFLAGS, X86::CondCode &CC,
   return SDValue();
 }
 
+// Attempt to fold some (truncate (srl (add X, C1), C2)) patterns to
+// (add (truncate (srl X, C2), C1')). C1' will be smaller than C1 so we are able
+// to avoid generating code with MOVABS and large constants in certain cases.
+static SDValue combineSetCCTruncAdd(SDValue EFLAGS, X86::CondCode &CC,
+                                    SelectionDAG &DAG) {
+  if (!(CC == X86::COND_E || CC == X86::COND_NE || CC == X86::COND_AE ||
+        CC == X86::COND_B))
+    return SDValue();
----------------
phoebewang wrote:

The title and above comment don't match the code. If the combine relies on setcc, we should mention it.

https://github.com/llvm/llvm-project/pull/126448