[llvm] [CodeLayout] Size-aware machine block placement (PR #109711)

[David Li via llvm-commits]

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@@ -3604,24 +3624,48 @@ void MachineBlockPlacement::applyExtTsp() {
     // not see a perf improvement with the exact block sizes.
     auto NonDbgInsts =
         instructionsWithoutDebug(MBB.instr_begin(), MBB.instr_end());
-    int NumInsts = std::distance(NonDbgInsts.begin(), NonDbgInsts.end());
+    size_t NumInsts = std::distance(NonDbgInsts.begin(), NonDbgInsts.end());
     BlockSizes[BlockIndex[&MBB]] = 4 * NumInsts;
     // Getting jump frequencies.
-    for (MachineBasicBlock *Succ : MBB.successors()) {
-      auto EP = MBPI->getEdgeProbability(&MBB, Succ);
-      BlockFrequency JumpFreq = BlockFreq * EP;
-      JumpCounts.push_back(
-          {BlockIndex[&MBB], BlockIndex[Succ], JumpFreq.getFrequency()});
+
+    if (!OptForSize) {
+      for (MachineBasicBlock *Succ : MBB.successors()) {
+        auto EP = MBPI->getEdgeProbability(&MBB, Succ);
+        BlockFrequency JumpFreq = BlockFreq * EP;
+        JumpCounts.push_back(
+            {BlockIndex[&MBB], BlockIndex[Succ], JumpFreq.getFrequency()});
+      }
+    } else {
+      Cond.clear();
+      MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For analyzeBranch.
+      if (TII->analyzeBranch(MBB, TBB, FBB, Cond))
+        continue;
+
+      const MachineBasicBlock *FTB = MBB.getFallThrough();
+
+      Succs.clear();
+      if (TBB && TBB != FTB)
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david-xl wrote:

add some comments on these three checks.

https://github.com/llvm/llvm-project/pull/109711