[mlir:DataFlowAnalysis] Reprocess the arguments of already executable edges

[rriddle]

Summary

This fixes a bug where we discover new information about the arguments of an
already executable edge, but don't visit the arguments. We only visit the arguments, and not the block itself, so this commit shouldn't really affect performance at all.

Fixes PR#51871

[mehdi_amini]

mlir/test/Transforms/sccp.mlir

182

information

mlir/lib/Analysis/DataFlowAnalysis.cpp

ChangeResult ForwardDataFlowSolver::markBlockExecutable(Block *block) {
   return marked ? ChangeResult::Change : ChangeResult::NoChange;
 }
 
 bool ForwardDataFlowSolver::isBlockExecutable(Block *block) const {
   return executableBlocks.count(block);
 }
 
 void ForwardDataFlowSolver::markEdgeExecutable(Block *from, Block *to) {
-  if (!executableEdges.insert(std::make_pair(from, to)).second)
-    return;
+  executableEdges.insert(std::make_pair(from, to));
 
   // Mark the destination as executable, and reprocess its arguments if it was
   // already executable.
   if (markBlockExecutable(to) == ChangeResult::NoChange) {
     for (int i : llvm::seq<int>(0, to->getNumArguments()))
       visitBlockArgument(to, i);
   }
 }

mlir/test/Transforms/sccp.mlir

^bb1(%iv: i32):
   cond_br %cond2, ^bb1(%res : i32), ^bb2(%res : i32)
 
 ^bb2(%arg : i32):
   // CHECK: ^bb2(%[[ARG:.*]]: i32):
   // CHECK: return %[[ARG]] : i32
 
   return %arg : i32
 }
+
+// Check that we reprocess executable edges when information changes.
+
+// CHECK-LABEL: func @recheck_executable_edge
+func @recheck_executable_edge(%cond0: i1) -> (i1, i1) {
+  %true = constant true
+  %false = constant false
+  cond_br %cond0, ^bb_1a, ^bb2(%false : i1)
+^bb_1a:
+  br ^bb2(%true : i1)
+
+^bb2(%x: i1):
+  // CHECK: ^bb2(%[[X:.*]]: i1):
+  br ^bb3(%x : i1)
+
+^bb3(%y: i1):
+  // CHECK: ^bb3(%[[Y:.*]]: i1):
+  // CHECK: return %[[X]], %[[Y]]
+  return %x, %y : i1, i1
+}