Currently, codegen may spent some time in SDISel passes even if an entire
function is successfully handled by fast-isel. That's because function
arguments are *always* handled by SDISel. Introduce FastLowerArguments to
allow each target to provide hook to handle formal argument lowering.
As a proof-of-concept, add ARMFastIsel::FastLowerArguments to handle
functions with 4 or fewer scalar integer (i8, i16, or i32) arguments. It
completely eliminates the need for SDISel for trivial functions.
rdar://13163905
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174855 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index d4e9a50..c9289ad 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -1032,10 +1032,6 @@
if (FuncInfo->MBB->isLandingPad())
PrepareEHLandingPad();
- // Lower any arguments needed in this block if this is the entry block.
- if (LLVMBB == &Fn.getEntryBlock())
- LowerArguments(LLVMBB);
-
// Before doing SelectionDAG ISel, see if FastISel has been requested.
if (FastIS) {
FastIS->startNewBlock();
@@ -1043,9 +1039,15 @@
// Emit code for any incoming arguments. This must happen before
// beginning FastISel on the entry block.
if (LLVMBB == &Fn.getEntryBlock()) {
- CurDAG->setRoot(SDB->getControlRoot());
- SDB->clear();
- CodeGenAndEmitDAG();
+ // Lower any arguments needed in this block if this is the entry block.
+ if (!FastIS->LowerArguments()) {
+ // Call target indepedent SDISel argument lowering code if the target
+ // specific routine is not successful.
+ LowerArguments(LLVMBB);
+ CurDAG->setRoot(SDB->getControlRoot());
+ SDB->clear();
+ CodeGenAndEmitDAG();
+ }
// If we inserted any instructions at the beginning, make a note of
// where they are, so we can be sure to emit subsequent instructions
@@ -1156,6 +1158,10 @@
}
FastIS->recomputeInsertPt();
+ } else {
+ // Lower any arguments needed in this block if this is the entry block.
+ if (LLVMBB == &Fn.getEntryBlock())
+ LowerArguments(LLVMBB);
}
if (Begin != BI)