[LLVMdev] Complex load patterns and token factors

[Tim Northover]

On Sat, Jun 23, 2012 at 04:10:51PM -0500, Hal Finkel wrote:
> Working on a target I added this pattern:
> 
> def : Pat<(v4i64 (load xoaddr:$src)),
>           (QVFCTIDb (QVLFDXb xoaddr:$src))>;
> 
> I'd like to fix this so that it works correctly: the TokenFactor
> inputs should be attached to all inner-most instructions. I'm guessing
> this is somewhere in SelectionDAGISel.cpp, but if someone has a
> more-specific idea, I'd appreciate hearing it.

I believe it's a current TableGen limitation. When generating its DAG
tables for this kind of thing, TableGen gives output instructions that
should take chain a special flag: Opfl_Chain.

Unfortunately the way it decides which instructions are worthy of this
flag is rather naive:
  + If an instruction has a built-in pattern (in the Instruciton
    record), it checks whether that makes use of a chain.
  + Otherwise, the outer instruction of the Pat gets a chain.

So if your QVLFDXb instruction doesn't set the Pattern(s?) field,
TableGen won't know it needs the chain.

There's a big comment just above the test about how the current
situation is rather broken. I'm currently inclined to add a check for
mayLoad and mayStore at that point in TableGeni (see patch), but was
waiting until I could give tests and justification on the list before
submitting it.

Tim.
-------------- next part --------------
diff --git a/utils/TableGen/DAGISelMatcherGen.cpp b/utils/TableGen/DAGISelMatcherGen.cpp
index 2ac7b87..4acd209 100644
--- a/utils/TableGen/DAGISelMatcherGen.cpp
+++ b/utils/TableGen/DAGISelMatcherGen.cpp
@@ -690,6 +690,12 @@ EmitResultInstructionAsOperand(const TreePatternNode *N,
   bool NodeHasChain = InstPatNode &&
                       InstPatNode->TreeHasProperty(SDNPHasChain, CGP);
 
+  // Instructions which load and store from memory should have a chain,
+  // regardless of whether they happen to have an internal pattern saying so.
+  if (Pattern.getSrcPattern()->TreeHasProperty(SDNPHasChain, CGP)
+      && (II.mayLoad || II.mayStore))
+      NodeHasChain = true;
+
   bool isRoot = N == Pattern.getDstPattern();
 
   // TreeHasOutGlue - True if this tree has glue.