[llvm] [MachineSink] Fix missing sinks along critical edges (PR #97618)

[Craig Topper via llvm-commits]

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@@ -887,6 +899,27 @@ bool MachineSinking::isWorthBreakingCriticalEdge(MachineInstr &MI,
   if (!MI.isCopy() && !TII->isAsCheapAsAMove(MI))
     return true;
 
+  // Check and record the register and the destination block we want to sink
+  // into. Note that we want to do the following before the next check on branch
+  // probability. Because we want to record the initial candidate even if it's
+  // on hot edge, so that other candidates that might not on hot edges can be
+  // sinked as well.
+  for (const auto &MO : MI.all_defs()) {
+    Register Reg = MO.getReg();
+    if (!Reg)
+      continue;
+    Register SrcReg = Reg.isVirtual() ? TRI->lookThruCopyLike(Reg, MRI) : Reg;
+    auto Key = std::make_pair(SrcReg, To);
+    auto Res = CEMergeCandidates.insert(std::make_pair(Key, From));
+    // We wanted to sink the same register into the same block, consider it to
+    // be profitable.
+    if (!Res.second) {
+      // Return the source block that was previously holded off.
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topperc wrote:

holded -> held

https://github.com/llvm/llvm-project/pull/97618