Enable hoisting load from constant memories.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89510 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/MachineLICM.cpp

@@ -34,16 +34,11 @@
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/Statistic.h"
-#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace llvm;
 
-static cl::opt<bool> HoistLdConst("licm-const-load",
-                                  cl::desc("LICM load from constant memory"),
-                                  cl::init(false), cl::Hidden);
-
 STATISTIC(NumHoisted, "Number of machine instructions hoisted out of loops");
 STATISTIC(NumCSEed,   "Number of hoisted machine instructions CSEed");
 
@@ -102,7 +97,7 @@ namespace {
 
     /// IsProfitableToHoist - Return true if it is potentially profitable to
     /// hoist the given loop invariant.
-    bool IsProfitableToHoist(MachineInstr &MI, bool &isConstLd);
+    bool IsProfitableToHoist(MachineInstr &MI);
 
     /// HoistRegion - Walk the specified region of the CFG (defined by all
     /// blocks dominated by the specified block, and that are in the current
@@ -367,9 +362,7 @@ bool MachineLICM::isLoadFromConstantMemory(MachineInstr *MI) {
 
 /// IsProfitableToHoist - Return true if it is potentially profitable to hoist
 /// the given loop invariant.
-bool MachineLICM::IsProfitableToHoist(MachineInstr &MI, bool &isConstLd) {
+bool MachineLICM::IsProfitableToHoist(MachineInstr &MI) {
-  isConstLd = false;
-
   if (MI.getOpcode() == TargetInstrInfo::IMPLICIT_DEF)
     return false;
 
@@ -382,9 +375,8 @@ bool MachineLICM::IsProfitableToHoist(MachineInstr &MI, bool &isConstLd) {
   // adding a store in the loop preheader. But the reload is no more expensive.
   // The side benefit is these loads are frequently CSE'ed.
   if (!TII->isTriviallyReMaterializable(&MI, AA)) {
-    if (!HoistLdConst || !isLoadFromConstantMemory(&MI))
+    if (!isLoadFromConstantMemory(&MI))
       return false;
-    isConstLd = true;
   }
 
   // If result(s) of this instruction is used by PHIs, then don't hoist it.
@@ -439,9 +431,7 @@ MachineInstr *MachineLICM::ExtractHoistableLoad(MachineInstr *MI) {
   MBB->insert(MI, NewMIs[1]);
   // If unfolding produced a load that wasn't loop-invariant or profitable to
   // hoist, discard the new instructions and bail.
-  bool isConstLd;
+  if (!IsLoopInvariantInst(*NewMIs[0]) || !IsProfitableToHoist(*NewMIs[0])) {
-  if (!IsLoopInvariantInst(*NewMIs[0]) ||
-      !IsProfitableToHoist(*NewMIs[0], isConstLd)) {
     NewMIs[0]->eraseFromParent();
     NewMIs[1]->eraseFromParent();
     return 0;
@@ -507,9 +497,7 @@ bool MachineLICM::EliminateCSE(MachineInstr *MI,
 ///
 void MachineLICM::Hoist(MachineInstr *MI) {
   // First check whether we should hoist this instruction.
-  bool isConstLd;
+  if (!IsLoopInvariantInst(*MI) || !IsProfitableToHoist(*MI)) {
-  if (!IsLoopInvariantInst(*MI) ||
-      !IsProfitableToHoist(*MI, isConstLd)) {
     // If not, try unfolding a hoistable load.
     MI = ExtractHoistableLoad(MI);
     if (!MI) return;
@@ -518,10 +506,7 @@ void MachineLICM::Hoist(MachineInstr *MI) {
   // Now move the instructions to the predecessor, inserting it before any
   // terminator instructions.
   DEBUG({
-      errs() << "Hoisting ";
+      errs() << "Hoisting " << *MI;
-      if (isConstLd)
-        errs() << "load from constant mem ";
-      errs() << *MI;
       if (CurPreheader->getBasicBlock())
         errs() << " to MachineBasicBlock "
                << CurPreheader->getName();

test/CodeGen/Thumb2/machine-licm.ll

@@ -18,7 +18,9 @@ entry:
 bb.nph:                                           ; preds = %entry
 ; CHECK: BB#1
 ; CHECK: ldr.n r2, LCPI1_0
-; CHECK: ldr r{{[0-9]+}}, [r2]
+; CHECK: ldr r3, [r2]
+; CHECK: ldr r3, [r3]
+; CHECK: ldr r2, [r2]
 ; CHECK: LBB1_2
 ; CHECK: LCPI1_0:
 ; CHECK-NOT: LCPI1_1:
@@ -27,7 +29,9 @@ bb.nph:                                           ; preds = %entry
 ; PIC: BB#1
 ; PIC: ldr.n r2, LCPI1_0
 ; PIC: add r2, pc
-; PIC: ldr r{{[0-9]+}}, [r2]
+; PIC: ldr r3, [r2]
+; PIC: ldr r3, [r3]
+; PIC: ldr r2, [r2]
 ; PIC: LBB1_2
 ; PIC: LCPI1_0:
 ; PIC-NOT: LCPI1_1:

test/CodeGen/X86/2009-10-08-MachineLICMBug.ll

@@ -1,4 +1,4 @@
-; RUN: llc < %s -mtriple=i386-apple-darwin -relocation-model=pic -stats |& grep {machine-licm} | grep 1
+; RUN: llc < %s -mtriple=i386-apple-darwin -relocation-model=pic -stats |& grep {machine-licm} | grep 2
 ; rdar://7274692
 
 %0 = type { [125 x i32] }

test/CodeGen/X86/pic-load-remat.ll

@@ -1,10 +1,4 @@
 ; RUN: llc < %s -mtriple=i686-apple-darwin -mattr=+sse2 -relocation-model=pic | grep psllw | grep pb
-; XFAIL: *
-
-; This is XFAIL'd because MachineLICM is now hoisting all of the loads, and the pic
-; base appears killed in the entry block when remat is making its decisions. Remat's
-; simple heuristic decides against rematting because it doesn't want to extend the
-; live-range of the pic base; this isn't necessarily optimal.
 
 define void @f() nounwind  {
 entry: