[Inline Spiller] Extend the snippet by statepoint uses

Snippet is a tiny live interval which has copy or fill like def
and copy or spill like use at the end (any of them might abcent).

Snippet has only one use/def inside interval and interval is located
in one basic block.

When inline spiller spills some reg around uses it also forces the
spilling of connected snippets those which got by splitting the
same original reg and its def is a full copy of our reg or its
last use is a full copy to our reg.

The definition of snippet is extended to allow not only one use/def
but more. However all other uses are statepoint instructions which will
fold fill into its operand. That way we do not introduce new fills/spills.

Reviewed By: qcolombet, dantrushin
Differential Revision: https://reviews.llvm.org/D138093

1 files changed, 20 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/InlineSpiller.cpp b/llvm/lib/CodeGen/InlineSpiller.cpp
index e80f0ab..5f582ee 100644
--- a/llvm/lib/CodeGen/InlineSpiller.cpp
+++ b/llvm/lib/CodeGen/InlineSpiller.cpp
@@ -280,13 +280,28 @@ bool InlineSpiller::isSnippet(const LiveInterval &SnipLI) {
   Register Reg = Edit->getReg();
 
   // A snippet is a tiny live range with only a single instruction using it
-  // besides copies to/from Reg or spills/fills. We accept:
+  // besides copies to/from Reg or spills/fills.
+  // Exception is done for statepoint instructions which will fold fills
+  // into their operands.
+  // We accept:
   //
   //   %snip = COPY %Reg / FILL fi#
   //   %snip = USE %snip
+  //   %snip = STATEPOINT %snip in var arg area
   //   %Reg = COPY %snip / SPILL %snip, fi#
   //
-  if (SnipLI.getNumValNums() > 2 || !LIS.intervalIsInOneMBB(SnipLI))
+  if (!LIS.intervalIsInOneMBB(SnipLI))
+    return false;
+
+  // Number of defs should not exceed 2 not accounting defs coming from
+  // statepoint instructions.
+  unsigned NumValNums = SnipLI.getNumValNums();
+  for (auto *VNI : SnipLI.vnis()) {
+    MachineInstr *MI = LIS.getInstructionFromIndex(VNI->def);
+    if (MI->getOpcode() == TargetOpcode::STATEPOINT)
+      --NumValNums;
+  }
+  if (NumValNums > 2)
     return false;
 
   MachineInstr *UseMI = nullptr;
@@ -311,6 +326,9 @@ bool InlineSpiller::isSnippet(const LiveInterval &SnipLI) {
     if (SnipLI.reg() == TII.isStoreToStackSlot(MI, FI) && FI == StackSlot)
       continue;
 
+    if (StatepointOpers::isFoldableReg(&MI, SnipLI.reg()))
+      continue;
+
     // Allow a single additional instruction.
     if (UseMI && &MI != UseMI)
       return false;