FastISel needs to remove dead code when it bails out.
When FastISel fails to translate an instruction it hands off code
generation to SelectionDAG. Before it does so, it may have generated
local value instructions to feed phi nodes in successor blocks. These
instructions will then be generated again by SelectionDAG, causing
duplication and less efficient code, including extra spill
instructions.
Patch by Wolfgang Pieb!
Differential Revision: http://reviews.llvm.org/D11768
llvm-svn: 255520
diff --git a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
index a70b6fd..98ce8d5 100644
--- a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -1322,12 +1322,38 @@
return true;
}
+// Remove local value instructions starting from the instruction after
+// SavedLastLocalValue to the current function insert point.
+void FastISel::removeDeadLocalValueCode(MachineInstr *SavedLastLocalValue)
+{
+ MachineInstr *CurLastLocalValue = getLastLocalValue();
+ if (CurLastLocalValue != SavedLastLocalValue) {
+ // Find the first local value instruction to be deleted.
+ // This is the instruction after SavedLastLocalValue if it is non-NULL.
+ // Otherwise it's the first instruction in the block.
+ MachineBasicBlock::iterator FirstDeadInst(SavedLastLocalValue);
+ if (SavedLastLocalValue)
+ ++FirstDeadInst;
+ else
+ FirstDeadInst = FuncInfo.MBB->getFirstNonPHI();
+ setLastLocalValue(SavedLastLocalValue);
+ removeDeadCode(FirstDeadInst, FuncInfo.InsertPt);
+ }
+}
+
bool FastISel::selectInstruction(const Instruction *I) {
+ MachineInstr *SavedLastLocalValue = getLastLocalValue();
// Just before the terminator instruction, insert instructions to
// feed PHI nodes in successor blocks.
if (isa<TerminatorInst>(I))
- if (!handlePHINodesInSuccessorBlocks(I->getParent()))
+ if (!handlePHINodesInSuccessorBlocks(I->getParent())) {
+ // PHI node handling may have generated local value instructions,
+ // even though it failed to handle all PHI nodes.
+ // We remove these instructions because SelectionDAGISel will generate
+ // them again.
+ removeDeadLocalValueCode(SavedLastLocalValue);
return false;
+ }
DbgLoc = I->getDebugLoc();
@@ -1376,8 +1402,12 @@
DbgLoc = DebugLoc();
// Undo phi node updates, because they will be added again by SelectionDAG.
- if (isa<TerminatorInst>(I))
+ if (isa<TerminatorInst>(I)) {
+ // PHI node handling may have generated local value instructions.
+ // We remove them because SelectionDAGISel will generate them again.
+ removeDeadLocalValueCode(SavedLastLocalValue);
FuncInfo.PHINodesToUpdate.resize(FuncInfo.OrigNumPHINodesToUpdate);
+ }
return false;
}