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/FastISel.cpp b/lib/CodeGen/SelectionDAG/FastISel.cpp
index 0d90a07..6c41e1b 100644
--- a/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -87,6 +87,27 @@
LastLocalValue = EmitStartPt;
}
+bool FastISel::LowerArguments() {
+ if (!FuncInfo.CanLowerReturn)
+ // Fallback to SDISel argument lowering code to deal with sret pointer
+ // parameter.
+ return false;
+
+ if (!FastLowerArguments())
+ return false;
+
+ // Enter non-dead arguments into ValueMap for uses in non-entry BBs.
+ for (Function::const_arg_iterator I = FuncInfo.Fn->arg_begin(),
+ E = FuncInfo.Fn->arg_end(); I != E; ++I) {
+ if (!I->use_empty()) {
+ DenseMap<const Value *, unsigned>::iterator VI = LocalValueMap.find(I);
+ assert(VI != LocalValueMap.end() && "Missed an argument?");
+ FuncInfo.ValueMap[I] = VI->second;
+ }
+ }
+ return true;
+}
+
void FastISel::flushLocalValueMap() {
LocalValueMap.clear();
LastLocalValue = EmitStartPt;
@@ -836,7 +857,8 @@
void
FastISel::FastEmitBranch(MachineBasicBlock *MSucc, DebugLoc DL) {
- if (FuncInfo.MBB->getBasicBlock()->size() > 1 && FuncInfo.MBB->isLayoutSuccessor(MSucc)) {
+ if (FuncInfo.MBB->getBasicBlock()->size() > 1 &&
+ FuncInfo.MBB->isLayoutSuccessor(MSucc)) {
// For more accurate line information if this is the only instruction
// in the block then emit it, otherwise we have the unconditional
// fall-through case, which needs no instructions.
@@ -1067,6 +1089,10 @@
FastISel::~FastISel() {}
+bool FastISel::FastLowerArguments() {
+ return false;
+}
+
unsigned FastISel::FastEmit_(MVT, MVT,
unsigned) {
return 0;
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)