[llvm] 05b0c76 - [NFC][MacroFusion] Adding the assertion if someone want to fuse more than 2 instructions

[QingShan Zhang via llvm-commits]

Author: QingShan Zhang
Date: 2019-12-10T03:10:21Z
New Revision: 05b0c76aa76ebdd77cae6c13aacb0079d49b4350

URL: https://github.com/llvm/llvm-project/commit/05b0c76aa76ebdd77cae6c13aacb0079d49b4350
DIFF: https://github.com/llvm/llvm-project/commit/05b0c76aa76ebdd77cae6c13aacb0079d49b4350.diff

LOG: [NFC][MacroFusion] Adding the assertion if someone want to fuse more than 2 instructions

As discussed in https://reviews.llvm.org/D69998, we miss to create some dependency edges
if chained more than 2 instructions. Adding an assertion here if someone want to chain
more than 2 instructions.

Differential Revision: https://reviews.llvm.org/D71180

Added: 
    

Modified: 
    llvm/lib/CodeGen/MacroFusion.cpp

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/MacroFusion.cpp b/llvm/lib/CodeGen/MacroFusion.cpp
index 26cbc14166be..d2ee21c8720f 100644
--- a/llvm/lib/CodeGen/MacroFusion.cpp
+++ b/llvm/lib/CodeGen/MacroFusion.cpp
@@ -71,6 +71,14 @@ static bool fuseInstructionPair(ScheduleDAGInstrs &DAG, SUnit &FirstSU,
   if (!DAG.addEdge(&SecondSU, SDep(&FirstSU, SDep::Cluster)))
     return false;
 
+  // TODO - If we want to chain more than two instructions, we need to create
+  // artifical edges to make dependencies from the FirstSU also dependent
+  // on other chained instructions, and other chained instructions also
+  // dependent on the dependencies of the SecondSU, to prevent them from being
+  // scheduled into these chained instructions.
+  assert(hasLessThanNumFused(FirstSU, 2) &&
+         "Currently we only support chaining together two instructions");
+
   // Adjust the latency between both instrs.
   for (SDep &SI : FirstSU.Succs)
     if (SI.getSUnit() == &SecondSU)