#include "llvm/CodeGen/LiveRangeEdit.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
/// This returns true if an interval was modified.
bool removeCopyByCommutingDef(const CoalescerPair &CP,MachineInstr *CopyMI);
+ /// We found a copy which can be moved to its less frequent predecessor.
+ bool removePartialRedundancy(const CoalescerPair &CP, MachineInstr &CopyMI);
+
/// If the source of a copy is defined by a
/// trivial computation, replace the copy by rematerialize the definition.
bool reMaterializeTrivialDef(const CoalescerPair &CP, MachineInstr *CopyMI,
return true;
}
+/// For copy B = A in BB2, if A is defined by A = B in BB0 which is a
+/// predecessor of BB2, and if B is not redefined on the way from A = B
+/// in BB2 to B = A in BB2, B = A in BB2 is partially redundant if the
+/// execution goes through the path from BB0 to BB2. We may move B = A
+/// to the predecessor without such reversed copy.
+/// So we will transform the program from:
+/// BB0:
+/// A = B; BB1:
+/// ... ...
+/// / \ /
+/// BB2:
+/// ...
+/// B = A;
+///
+/// to:
+///
+/// BB0: BB1:
+/// A = B; ...
+/// ... B = A;
+/// / \ /
+/// BB2:
+/// ...
+///
+/// A special case is when BB0 and BB2 are the same BB which is the only
+/// BB in a loop:
+/// BB1:
+/// ...
+/// BB0/BB2: ----
+/// B = A; |
+/// ... |
+/// A = B; |
+/// |-------
+/// |
+/// We may hoist B = A from BB0/BB2 to BB1.
+///
+/// The major preconditions for correctness to remove such partial
+/// redundancy include:
+/// 1. A in B = A in BB2 is defined by a PHI in BB2, and one operand of
+/// the PHI is defined by the reversed copy A = B in BB0.
+/// 2. No B is referenced from the start of BB2 to B = A.
+/// 3. No B is defined from A = B to the end of BB0.
+/// 4. BB1 has only one successor.
+///
+/// 2 and 4 implicitly ensure B is not live at the end of BB1.
+/// 4 guarantees BB2 is hotter than BB1, so we can only move a copy to a
+/// colder place, which not only prevent endless loop, but also make sure
+/// the movement of copy is beneficial.
+bool RegisterCoalescer::removePartialRedundancy(const CoalescerPair &CP,
+ MachineInstr &CopyMI) {
+ assert(!CP.isPhys());
+ if (!CopyMI.isFullCopy())
+ return false;
+
+ MachineBasicBlock &MBB = *CopyMI.getParent();
+ if (MBB.isEHPad())
+ return false;
+
+ if (MBB.pred_size() != 2)
+ return false;
+
+ LiveInterval &IntA =
+ LIS->getInterval(CP.isFlipped() ? CP.getDstReg() : CP.getSrcReg());
+ LiveInterval &IntB =
+ LIS->getInterval(CP.isFlipped() ? CP.getSrcReg() : CP.getDstReg());
+
+ // A is defined by PHI at the entry of MBB.
+ SlotIndex CopyIdx = LIS->getInstructionIndex(CopyMI).getRegSlot(true);
+ VNInfo *AValNo = IntA.getVNInfoAt(CopyIdx);
+ assert(AValNo && !AValNo->isUnused() && "COPY source not live");
+ if (!AValNo->isPHIDef())
+ return false;
+
+ // No B is referenced before CopyMI in MBB.
+ if (IntB.overlaps(LIS->getMBBStartIdx(&MBB), CopyIdx))
+ return false;
+
+ // MBB has two predecessors: one contains A = B so no copy will be inserted
+ // for it. The other one will have a copy moved from MBB.
+ bool FoundReverseCopy = false;
+ MachineBasicBlock *CopyLeftBB = nullptr;
+ for (MachineBasicBlock *Pred : MBB.predecessors()) {
+ VNInfo *PVal = IntA.getVNInfoBefore(LIS->getMBBEndIdx(Pred));
+ MachineInstr *DefMI = LIS->getInstructionFromIndex(PVal->def);
+ if (!DefMI || !DefMI->isFullCopy()) {
+ CopyLeftBB = Pred;
+ continue;
+ }
+ // Check DefMI is a reverse copy and it is in BB Pred.
+ if (DefMI->getOperand(0).getReg() != IntA.reg ||
+ DefMI->getOperand(1).getReg() != IntB.reg ||
+ DefMI->getParent() != Pred) {
+ CopyLeftBB = Pred;
+ continue;
+ }
+ // If there is any other def of B after DefMI and before the end of Pred,
+ // we need to keep the copy of B = A at the end of Pred if we remove
+ // B = A from MBB.
+ bool ValB_Changed = false;
+ for (auto VNI : IntB.valnos) {
+ if (VNI->isUnused())
+ continue;
+ if (PVal->def < VNI->def && VNI->def < LIS->getMBBEndIdx(Pred)) {
+ ValB_Changed = true;
+ break;
+ }
+ }
+ if (ValB_Changed) {
+ CopyLeftBB = Pred;
+ continue;
+ }
+ FoundReverseCopy = true;
+ }
+
+ // If no reverse copy is found in predecessors, nothing to do.
+ if (!FoundReverseCopy)
+ return false;
+
+ // If CopyLeftBB is nullptr, it means every predecessor of MBB contains
+ // reverse copy, CopyMI can be removed trivially if only IntA/IntB is updated.
+ // If CopyLeftBB is not nullptr, move CopyMI from MBB to CopyLeftBB and
+ // update IntA/IntB.
+ //
+ // If CopyLeftBB is not nullptr, ensure CopyLeftBB has a single succ so
+ // MBB is hotter than CopyLeftBB.
+ if (CopyLeftBB && CopyLeftBB->succ_size() > 1)
+ return false;
+
+ // Now ok to move copy.
+ if (CopyLeftBB) {
+ DEBUG(dbgs() << "\tremovePartialRedundancy: Move the copy to BB#"
+ << CopyLeftBB->getNumber() << '\t' << CopyMI);
+
+ // Insert new copy to CopyLeftBB.
+ auto InsPos = CopyLeftBB->getFirstTerminator();
+ MachineInstr *NewCopyMI = BuildMI(*CopyLeftBB, InsPos, CopyMI.getDebugLoc(),
+ TII->get(TargetOpcode::COPY), IntB.reg)
+ .addReg(IntA.reg);
+ SlotIndex NewCopyIdx =
+ LIS->InsertMachineInstrInMaps(*NewCopyMI).getRegSlot();
+ VNInfo *VNI = IntB.getNextValue(NewCopyIdx, LIS->getVNInfoAllocator());
+ IntB.createDeadDef(VNI);
+ } else {
+ DEBUG(dbgs() << "\tremovePartialRedundancy: Remove the copy from BB#"
+ << MBB.getNumber() << '\t' << CopyMI);
+ }
+
+ // Remove CopyMI.
+ SlotIndex EndPoint = IntB.Query(CopyIdx.getRegSlot()).endPoint();
+ LIS->removeVRegDefAt(IntB, CopyIdx.getRegSlot());
+ LIS->RemoveMachineInstrFromMaps(CopyMI);
+ CopyMI.eraseFromParent();
+
+ // Extend IntB to the EndPoint of its original live interval.
+ SmallVector<SlotIndex, 8> EndPoints;
+ EndPoints.push_back(EndPoint);
+ LIS->extendToIndices(IntB, EndPoints);
+
+ shrinkToUses(&IntA);
+ return true;
+}
+
/// Returns true if @p MI defines the full vreg @p Reg, as opposed to just
/// defining a subregister.
static bool definesFullReg(const MachineInstr &MI, unsigned Reg) {
}
}
+ // Try and see if we can partially eliminate the copy by moving the copy to
+ // its predecessor.
+ if (!CP.isPartial() && !CP.isPhys())
+ if (removePartialRedundancy(CP, *CopyMI))
+ return true;
+
// Otherwise, we are unable to join the intervals.
DEBUG(dbgs() << "\tInterference!\n");
Again = true; // May be possible to coalesce later.
--- /dev/null
+; RUN: llc -regalloc=greedy -mtriple=x86_64-unknown-linux-gnu < %s -o - | FileCheck %s
+;
+; The test is to check no redundent mov as follows will be generated in %while.body loop.
+; .LBB0_2:
+; movsbl %cl, %ecx
+; movl %edx, %eax ==> This movl can be promoted outside of loop.
+; shll $5, %eax
+; ...
+; movl %eax, %edx
+; jne .LBB0_2
+;
+; CHECK-LABEL: foo:
+; CHECK: [[L0:.LBB0_[0-9]+]]: # %while.body
+; CHECK: movl %[[REGA:.*]], %[[REGB:.*]]
+; CHECK-NOT: movl %[[REGB]], %[[REGA]]
+; CHECK: jne [[L0]]
+;
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+@b = common local_unnamed_addr global i8* null, align 8
+@a = common local_unnamed_addr global i32 0, align 4
+
+define i32 @foo() local_unnamed_addr {
+entry:
+ %t0 = load i8*, i8** @b, align 8
+ %t1 = load i8, i8* %t0, align 1
+ %cmp4 = icmp eq i8 %t1, 0
+ %t2 = load i32, i32* @a, align 4
+ br i1 %cmp4, label %while.end, label %while.body.preheader
+
+while.body.preheader: ; preds = %entry
+ br label %while.body
+
+while.body: ; preds = %while.body.preheader, %while.body
+ %t3 = phi i32 [ %add3, %while.body ], [ %t2, %while.body.preheader ]
+ %t4 = phi i8 [ %t5, %while.body ], [ %t1, %while.body.preheader ]
+ %conv = sext i8 %t4 to i32
+ %add = mul i32 %t3, 33
+ %add3 = add nsw i32 %add, %conv
+ store i32 %add3, i32* @a, align 4
+ %t5 = load i8, i8* %t0, align 1
+ %cmp = icmp eq i8 %t5, 0
+ br i1 %cmp, label %while.end.loopexit, label %while.body
+
+while.end.loopexit: ; preds = %while.body
+ br label %while.end
+
+while.end: ; preds = %while.end.loopexit, %entry
+ %.lcssa = phi i32 [ %t2, %entry ], [ %add3, %while.end.loopexit ]
+ ret i32 %.lcssa
+}
--- /dev/null
+# RUN: llc -mtriple=x86_64-unknown-linux-gnu -run-pass simple-register-coalescing -o - %s | FileCheck %s
+# Check there is no partial redundent copy left in the loop after register coalescing.
+--- |
+ ; ModuleID = '<stdin>'
+ source_filename = "<stdin>"
+ target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+ target triple = "x86_64-unknown-linux-gnu"
+
+ @b = common local_unnamed_addr global i8* null, align 8
+ @a = common local_unnamed_addr global i32 0, align 4
+
+ define i32 @foo() local_unnamed_addr {
+ entry:
+ %t0 = load i8*, i8** @b, align 8
+ %t1 = load i8, i8* %t0, align 1
+ %cmp4 = icmp eq i8 %t1, 0
+ %t2 = load i32, i32* @a, align 4
+ br i1 %cmp4, label %while.end, label %while.body.preheader
+
+ while.body.preheader: ; preds = %entry
+ br label %while.body
+
+ while.body: ; preds = %while.body, %while.body.preheader
+ %t3 = phi i32 [ %add3, %while.body ], [ %t2, %while.body.preheader ]
+ %t4 = phi i8 [ %t5, %while.body ], [ %t1, %while.body.preheader ]
+ %conv = sext i8 %t4 to i32
+ %add = mul i32 %t3, 33
+ %add3 = add nsw i32 %add, %conv
+ store i32 %add3, i32* @a, align 4
+ %t5 = load i8, i8* %t0, align 1
+ %cmp = icmp eq i8 %t5, 0
+ br i1 %cmp, label %while.end, label %while.body
+
+ while.end: ; preds = %while.body, %entry
+ %.lcssa = phi i32 [ %t2, %entry ], [ %add3, %while.body ]
+ ret i32 %.lcssa
+ }
+
+...
+---
+# Check A = B and B = A copies will not exist in the loop at the same time.
+# CHECK: name: foo
+# CHECK: [[L1:bb.3.while.body]]:
+# CHECK: %[[REGA:.*]] = COPY %[[REGB:.*]]
+# CHECK-NOT: %[[REGB]] = COPY %[[REGA]]
+# CHECK: JNE_1 %[[L1]]
+
+name: foo
+alignment: 4
+exposesReturnsTwice: false
+legalized: false
+regBankSelected: false
+selected: false
+tracksRegLiveness: true
+registers:
+ - { id: 0, class: gr64 }
+ - { id: 1, class: gr8 }
+ - { id: 2, class: gr32 }
+ - { id: 3, class: gr32 }
+ - { id: 4, class: gr8 }
+ - { id: 5, class: gr32 }
+ - { id: 6, class: gr8 }
+ - { id: 7, class: gr32 }
+ - { id: 8, class: gr32 }
+ - { id: 9, class: gr32 }
+ - { id: 10, class: gr32 }
+ - { id: 11, class: gr32 }
+ - { id: 12, class: gr8 }
+ - { id: 13, class: gr32 }
+frameInfo:
+ isFrameAddressTaken: false
+ isReturnAddressTaken: false
+ hasStackMap: false
+ hasPatchPoint: false
+ stackSize: 0
+ offsetAdjustment: 0
+ maxAlignment: 0
+ adjustsStack: false
+ hasCalls: false
+ maxCallFrameSize: 0
+ hasOpaqueSPAdjustment: false
+ hasVAStart: false
+ hasMustTailInVarArgFunc: false
+body: |
+ bb.0.entry:
+ successors: %bb.4(0x30000000), %bb.1.while.body.preheader(0x50000000)
+
+ %0 = MOV64rm %rip, 1, _, @b, _ :: (dereferenceable load 8 from @b)
+ %12 = MOV8rm %0, 1, _, 0, _ :: (load 1 from %ir.t0)
+ TEST8rr %12, %12, implicit-def %eflags
+ %11 = MOV32rm %rip, 1, _, @a, _ :: (dereferenceable load 4 from @a)
+ JNE_1 %bb.1.while.body.preheader, implicit killed %eflags
+
+ bb.4:
+ successors: %bb.3.while.end(0x80000000)
+
+ %10 = COPY %11
+ JMP_1 %bb.3.while.end
+
+ bb.1.while.body.preheader:
+ successors: %bb.2.while.body(0x80000000)
+
+ bb.2.while.body:
+ successors: %bb.3.while.end(0x04000000), %bb.2.while.body(0x7c000000)
+
+ %8 = MOVSX32rr8 %12
+ %10 = COPY %11
+ %10 = SHL32ri %10, 5, implicit-def dead %eflags
+ %10 = ADD32rr %10, %11, implicit-def dead %eflags
+ %10 = ADD32rr %10, %8, implicit-def dead %eflags
+ MOV32mr %rip, 1, _, @a, _, %10 :: (store 4 into @a)
+ %12 = MOV8rm %0, 1, _, 0, _ :: (load 1 from %ir.t0)
+ TEST8rr %12, %12, implicit-def %eflags
+ %11 = COPY %10
+ JNE_1 %bb.2.while.body, implicit killed %eflags
+ JMP_1 %bb.3.while.end
+
+ bb.3.while.end:
+ %eax = COPY %10
+ RET 0, killed %eax
+
+...
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