[llvm] [PowerPC] Emit lxvkq and vsrq instructions for build vector patterns (PR #157625)

[via llvm-commits]

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@@ -15657,6 +15664,133 @@ combineElementTruncationToVectorTruncation(SDNode *N,
   return SDValue();
 }
 
+// LXVKQ instruction load VSX vector with a special quadword value
+// based on an immediate value. This helper method returns the details of the
+// match as a tuple of {LXVKQ unsigned IMM Value, right_shift_amount}
+// to help generate the LXVKQ instruction and the subsequent shift instruction
+// required to match the original build vector pattern.
+
+// LXVKQPattern: {LXVKQ unsigned IMM Value, right_shift_amount}
+using LXVKQPattern = std::tuple<uint32_t, uint8_t>;
+
+static std::optional<LXVKQPattern> getPatternInfo(const APInt &FullVal) {
+
+  static const auto BaseLXVKQPatterns = []() {
+    // LXVKQ instruction loads the Quadword value:
+    // 0x8000_0000_0000_0000_0000_0000_0000_0000 when imm = 0b10000
+    return std::array<std::pair<APInt, uint32_t>, 1>{
+        {{APInt(128, 0x8000000000000000ULL) << 64, 16}}};
+  }();
+
+  // Check for direct LXVKQ match (no shift needed)
+  for (const auto &[BasePattern, Uim] : BaseLXVKQPatterns) {
+    if (FullVal == BasePattern)
+      return std::make_tuple(Uim, uint8_t{0});
+  }
+
+  // Check if FullValue can be generated by (right) shifting a base pattern
+  for (const auto &[BasePattern, Uim] : BaseLXVKQPatterns) {
+    if (BasePattern.lshr(127) == FullVal)
+      return std::make_tuple(Uim, uint8_t{127});
+  }
+
+  return std::nullopt;
+}
+
+/// Combine vector loads to a single load by recognising patterns in the Build
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RolandF77 wrote:

to a single load or a shift of a constant?

https://github.com/llvm/llvm-project/pull/157625