[PowerPC] Remove redundant TOC saves
This patch adds a peep hole optimization to remove any redundant toc save
instructions added as part of the call sequence for indirect calls. It removes
any toc saves within a function that are dominated by another toc save.
Differential Revision: https://reviews.llvm.org/D39736
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@319087 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/PowerPC/PPCMIPeephole.cpp b/lib/Target/PowerPC/PPCMIPeephole.cpp
index 0a84fe3..a8d9813 100644
--- a/lib/Target/PowerPC/PPCMIPeephole.cpp
+++ b/lib/Target/PowerPC/PPCMIPeephole.cpp
@@ -29,13 +29,15 @@
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/Debug.h"
-#include "llvm/ADT/Statistic.h"
#include "MCTargetDesc/PPCPredicates.h"
using namespace llvm;
#define DEBUG_TYPE "ppc-mi-peepholes"
+STATISTIC(RemoveTOCSave, "Number of TOC saves removed");
+STATISTIC(MultiTOCSaves,
+ "Number of functions with multiple TOC saves that must be kept");
STATISTIC(NumEliminatedSExt, "Number of eliminated sign-extensions");
STATISTIC(NumEliminatedZExt, "Number of eliminated zero-extensions");
STATISTIC(NumOptADDLIs, "Number of optimized ADD instruction fed by LI");
@@ -78,7 +80,9 @@
// Perform peepholes.
bool eliminateRedundantCompare(void);
-
+ bool eliminateRedundantTOCSaves(std::map<MachineInstr *, bool> &TOCSaves);
+ void UpdateTOCSaves(std::map<MachineInstr *, bool> &TOCSaves,
+ MachineInstr *MI);
// Find the "true" register represented by SrcReg (following chains
// of copies and subreg_to_reg operations).
unsigned lookThruCopyLike(unsigned SrcReg);
@@ -176,10 +180,37 @@
return 0;
}
+// This function maintains a map for the pairs <TOC Save Instr, Keep>
+// Each time a new TOC save is encountered, it checks if any of the exisiting
+// ones are dominated by the new one. If so, it marks the exisiting one as
+// redundant by setting it's entry in the map as false. It then adds the new
+// instruction to the map with either true or false depending on if any
+// exisiting instructions dominated the new one.
+void PPCMIPeephole::UpdateTOCSaves(
+ std::map<MachineInstr *, bool> &TOCSaves, MachineInstr *MI) {
+ assert(TII->isTOCSaveMI(*MI) && "Expecting a TOC save instruction here");
+ bool Keep = true;
+ for (auto It = TOCSaves.begin(); It != TOCSaves.end(); It++ ) {
+ MachineInstr *CurrInst = It->first;
+ // If new instruction dominates an exisiting one, mark exisiting one as
+ // redundant.
+ if (It->second && MDT->dominates(MI, CurrInst))
+ It->second = false;
+ // Check if the new instruction is redundant.
+ if (MDT->dominates(CurrInst, MI)) {
+ Keep = false;
+ break;
+ }
+ }
+ // Add new instruction to map.
+ TOCSaves[MI] = Keep;
+}
+
// Perform peephole optimizations.
bool PPCMIPeephole::simplifyCode(void) {
bool Simplified = false;
MachineInstr* ToErase = nullptr;
+ std::map<MachineInstr *, bool> TOCSaves;
for (MachineBasicBlock &MBB : *MF) {
for (MachineInstr &MI : MBB) {
@@ -201,6 +232,18 @@
default:
break;
+ case PPC::STD: {
+ MachineFrameInfo &MFI = MF->getFrameInfo();
+ if (MFI.hasVarSizedObjects() ||
+ !MF->getSubtarget<PPCSubtarget>().isELFv2ABI())
+ break;
+ // When encountering a TOC save instruction, call UpdateTOCSaves
+ // to add it to the TOCSaves map and mark any exisiting TOC saves
+ // it dominates as redundant.
+ if (TII->isTOCSaveMI(MI))
+ UpdateTOCSaves(TOCSaves, &MI);
+ break;
+ }
case PPC::XXPERMDI: {
// Perform simplifications of 2x64 vector swaps and splats.
// A swap is identified by an immediate value of 2, and a splat
@@ -683,6 +726,8 @@
}
}
+ // Eliminate all the TOC save instructions which are redundant.
+ Simplified |= eliminateRedundantTOCSaves(TOCSaves);
// We try to eliminate redundant compare instruction.
Simplified |= eliminateRedundantCompare();
@@ -888,6 +933,30 @@
return false;
}
+// This function will iterate over the input map containing a pair of TOC save
+// instruction and a flag. The flag will be set to false if the TOC save is proven
+// redundant. This function will erase from the basic block all the TOC saves
+// marked as redundant.
+bool PPCMIPeephole::eliminateRedundantTOCSaves(
+ std::map<MachineInstr *, bool> &TOCSaves) {
+ bool Simplified = false;
+ int NumKept = 0;
+ for (auto TOCSave : TOCSaves) {
+ if (!TOCSave.second) {
+ TOCSave.first->eraseFromParent();
+ RemoveTOCSave++;
+ Simplified = true;
+ } else {
+ NumKept++;
+ }
+ }
+
+ if (NumKept > 1)
+ MultiTOCSaves++;
+
+ return Simplified;
+}
+
// If multiple conditional branches are executed based on the (essentially)
// same comparison, we merge compare instructions into one and make multiple
// conditional branches on this comparison.
