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Re-commit r124462 with fixes. Tail recursion elim will now dup ret into unconditional predecessor to enable TCE on demand.

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llvm-svn: 124518
This commit is contained in:
Evan Cheng 2011-01-29 01:29:26 +00:00
parent 72f17d97f3
commit a1e4cb5f09
13 changed files with 223 additions and 73 deletions
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13
include/llvm/Transforms/Utils/BasicBlockUtils.h
View File

@ -22,9 +22,10 @@
namespace llvm {
class AliasAnalysis;
class Instruction;
class Pass;
class AliasAnalysis;
class ReturnInst;
/// DeleteDeadBlock - Delete the specified block, which must have no
/// predecessors.
@ -171,7 +172,15 @@ BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P);
BasicBlock *SplitBlockPredecessors(BasicBlock *BB, BasicBlock *const *Preds,
unsigned NumPreds, const char *Suffix,
Pass *P = 0);
/// FoldReturnIntoUncondBranch - This method duplicates the specified return
/// instruction into a predecessor which ends in an unconditional branch. If
/// the return instruction returns a value defined by a PHI, propagate the
/// right value into the return. It returns the new return instruction in the
/// predecessor.
ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
BasicBlock *Pred);
} // End llvm namespace
#endif

11
lib/CodeGen/TailDuplication.cpp
View File

@ -465,9 +465,12 @@ TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
MaxDuplicateCount = TailDuplicateSize;
if (PreRegAlloc) {
// Pre-regalloc tail duplication hurts compile time and doesn't help
// much except for indirect branches.
if (TailBB->empty() || !TailBB->back().getDesc().isIndirectBranch())
if (TailBB->empty())
return false;
const TargetInstrDesc &TID = TailBB->back().getDesc();
// Pre-regalloc tail duplication hurts compile time and doesn't help
// much except for indirect branches and returns.
if (!TID.isIndirectBranch() && !TID.isReturn())
return false;
// If the target has hardware branch prediction that can handle indirect
// branches, duplicating them can often make them predictable when there
@ -502,7 +505,7 @@ TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
}
// Heuristically, don't tail-duplicate calls if it would expand code size,
// as it's less likely to be worth the extra cost.
if (InstrCount > 1 && HasCall)
if (InstrCount > 1 && (PreRegAlloc && HasCall))
return false;
DEBUG(dbgs() << "\n*** Tail-duplicating BB#" << TailBB->getNumber() << '\n');

124
lib/Transforms/Scalar/TailRecursionElimination.cpp
View File

@ -52,11 +52,13 @@
#define DEBUG_TYPE "tailcallelim"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/CaptureTracking.h"
#include "llvm/Analysis/InlineCost.h"
@ -64,7 +66,9 @@
#include "llvm/Analysis/Loads.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
STATISTIC(NumEliminated, "Number of tail calls removed");
@ -80,6 +84,18 @@ namespace {
virtual bool runOnFunction(Function &F);
private:
CallInst *FindTRECandidate(Instruction *I,
bool CannotTailCallElimCallsMarkedTail);
bool EliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret,
BasicBlock *&OldEntry,
bool &TailCallsAreMarkedTail,
SmallVector<PHINode*, 8> &ArgumentPHIs,
bool CannotTailCallElimCallsMarkedTail);
bool FoldReturnAndProcessPred(BasicBlock *BB,
ReturnInst *Ret, BasicBlock *&OldEntry,
bool &TailCallsAreMarkedTail,
SmallVector<PHINode*, 8> &ArgumentPHIs,
bool CannotTailCallElimCallsMarkedTail);
bool ProcessReturningBlock(ReturnInst *RI, BasicBlock *&OldEntry,
bool &TailCallsAreMarkedTail,
SmallVector<PHINode*, 8> &ArgumentPHIs,
@ -136,7 +152,6 @@ bool TailCallElim::runOnFunction(Function &F) {
bool TailCallsAreMarkedTail = false;
SmallVector<PHINode*, 8> ArgumentPHIs;
bool MadeChange = false;
bool FunctionContainsEscapingAllocas = false;
// CannotTCETailMarkedCall - If true, we cannot perform TCE on tail calls
@ -163,10 +178,17 @@ bool TailCallElim::runOnFunction(Function &F) {
return false;
// Second pass, change any tail calls to loops.
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator()))
MadeChange |= ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail,
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator())) {
bool Change = ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail,
ArgumentPHIs,CannotTCETailMarkedCall);
if (!Change && BB->getFirstNonPHIOrDbg() == Ret)
Change = FoldReturnAndProcessPred(BB, Ret, OldEntry,
TailCallsAreMarkedTail, ArgumentPHIs,
CannotTCETailMarkedCall);
MadeChange |= Change;
}
}
// If we eliminated any tail recursions, it's possible that we inserted some
// silly PHI nodes which just merge an initial value (the incoming operand)
@ -325,41 +347,47 @@ Value *TailCallElim::CanTransformAccumulatorRecursion(Instruction *I,
return getCommonReturnValue(cast<ReturnInst>(I->use_back()), CI);
}
bool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry,
bool &TailCallsAreMarkedTail,
SmallVector<PHINode*, 8> &ArgumentPHIs,
bool CannotTailCallElimCallsMarkedTail) {
BasicBlock *BB = Ret->getParent();
static Instruction *FirstNonDbg(BasicBlock::iterator I) {
while (isa<DbgInfoIntrinsic>(I))
++I;
return &*I;
}
CallInst*
TailCallElim::FindTRECandidate(Instruction *TI,
bool CannotTailCallElimCallsMarkedTail) {
BasicBlock *BB = TI->getParent();
Function *F = BB->getParent();
if (&BB->front() == Ret) // Make sure there is something before the ret...
return false;
if (&BB->front() == TI) // Make sure there is something before the terminator.
return 0;
// Scan backwards from the return, checking to see if there is a tail call in
// this block. If so, set CI to it.
CallInst *CI;
BasicBlock::iterator BBI = Ret;
while (1) {
CallInst *CI = 0;
BasicBlock::iterator BBI = TI;
while (true) {
CI = dyn_cast<CallInst>(BBI);
if (CI && CI->getCalledFunction() == F)
break;
if (BBI == BB->begin())
return false; // Didn't find a potential tail call.
return 0; // Didn't find a potential tail call.
--BBI;
}
// If this call is marked as a tail call, and if there are dynamic allocas in
// the function, we cannot perform this optimization.
if (CI->isTailCall() && CannotTailCallElimCallsMarkedTail)
return false;
return 0;
// As a special case, detect code like this:
// double fabs(double f) { return __builtin_fabs(f); } // a 'fabs' call
// and disable this xform in this case, because the code generator will
// lower the call to fabs into inline code.
if (BB == &F->getEntryBlock() &&
&BB->front() == CI && &*++BB->begin() == Ret &&
FirstNonDbg(BB->front()) == CI &&
FirstNonDbg(llvm::next(BB->begin())) == TI &&
callIsSmall(F)) {
// A single-block function with just a call and a return. Check that
// the arguments match.
@ -370,9 +398,17 @@ bool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry,
for (; I != E && FI != FE; ++I, ++FI)
if (*I != &*FI) break;
if (I == E && FI == FE)
return false;
return 0;
}
return CI;
}
bool TailCallElim::EliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret,
BasicBlock *&OldEntry,
bool &TailCallsAreMarkedTail,
SmallVector<PHINode*, 8> &ArgumentPHIs,
bool CannotTailCallElimCallsMarkedTail) {
// If we are introducing accumulator recursion to eliminate operations after
// the call instruction that are both associative and commutative, the initial
// value for the accumulator is placed in this variable. If this value is set
@ -390,7 +426,8 @@ bool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry,
// tail call if all of the instructions between the call and the return are
// movable to above the call itself, leaving the call next to the return.
// Check that this is the case now.
for (BBI = CI, ++BBI; &*BBI != Ret; ++BBI) {
BasicBlock::iterator BBI = CI;
for (++BBI; &*BBI != Ret; ++BBI) {
if (CanMoveAboveCall(BBI, CI)) continue;
// If we can't move the instruction above the call, it might be because it
@ -427,6 +464,9 @@ bool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry,
return false;
}
BasicBlock *BB = Ret->getParent();
Function *F = BB->getParent();
// OK! We can transform this tail call. If this is the first one found,
// create the new entry block, allowing us to branch back to the old entry.
if (OldEntry == 0) {
@ -536,3 +576,49 @@ bool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry,
++NumEliminated;
return true;
}
bool TailCallElim::FoldReturnAndProcessPred(BasicBlock *BB,
ReturnInst *Ret, BasicBlock *&OldEntry,
bool &TailCallsAreMarkedTail,
SmallVector<PHINode*, 8> &ArgumentPHIs,
bool CannotTailCallElimCallsMarkedTail) {
bool Change = false;
// If the return block contains nothing but the return and PHI's,
// there might be an opportunity to duplicate the return in its
// predecessors and perform TRC there. Look for predecessors that end
// in unconditional branch and recursive call(s).
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB);
PI != E; ++PI) {
BasicBlock *Pred = *PI;
TerminatorInst *PTI = Pred->getTerminator();
if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
CallInst *CI = 0;
if (BI->isUnconditional() &&
(CI = FindTRECandidate(BI, CannotTailCallElimCallsMarkedTail))) {
DEBUG(dbgs() << "FOLDING: " << *BB
<< "INTO UNCOND BRANCH PRED: " << *Pred);
EliminateRecursiveTailCall(CI,
FoldReturnIntoUncondBranch(Ret, BB, Pred),
OldEntry, TailCallsAreMarkedTail, ArgumentPHIs,
CannotTailCallElimCallsMarkedTail);
Change = true;
}
}
}
return Change;
}
bool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry,
bool &TailCallsAreMarkedTail,
SmallVector<PHINode*, 8> &ArgumentPHIs,
bool CannotTailCallElimCallsMarkedTail) {
CallInst *CI = FindTRECandidate(Ret, CannotTailCallElimCallsMarkedTail);
if (!CI)
return false;
return EliminateRecursiveTailCall(CI, Ret, OldEntry, TailCallsAreMarkedTail,
ArgumentPHIs,
CannotTailCallElimCallsMarkedTail);
}

31
lib/Transforms/Utils/BasicBlockUtils.cpp
View File

@ -509,7 +509,32 @@ void llvm::FindFunctionBackedges(const Function &F,
// Go up one level.
InStack.erase(VisitStack.pop_back_val().first);
}
} while (!VisitStack.empty());
} while (!VisitStack.empty());
}
/// FoldReturnIntoUncondBranch - This method duplicates the specified return
/// instruction into a predecessor which ends in an unconditional branch. If
/// the return instruction returns a value defined by a PHI, propagate the
/// right value into the return. It returns the new return instruction in the
/// predecessor.
ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
BasicBlock *Pred) {
Instruction *UncondBranch = Pred->getTerminator();
// Clone the return and add it to the end of the predecessor.
Instruction *NewRet = RI->clone();
Pred->getInstList().push_back(NewRet);
// If the return instruction returns a value, and if the value was a
// PHI node in "BB", propagate the right value into the return.
for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
i != e; ++i)
if (PHINode *PN = dyn_cast<PHINode>(*i))
if (PN->getParent() == BB)
*i = PN->getIncomingValueForBlock(Pred);
// Update any PHI nodes in the returning block to realize that we no
// longer branch to them.
BB->removePredecessor(Pred);
UncondBranch->eraseFromParent();
return cast<ReturnInst>(NewRet);
}

25
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -28,6 +28,7 @@
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ConstantRange.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
@ -36,6 +37,10 @@
#include <map>
using namespace llvm;
static cl::opt<bool>
DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
cl::desc("Duplicate return instructions into unconditional branches"));
STATISTIC(NumSpeculations, "Number of speculative executed instructions");
namespace {
@ -2027,28 +2032,12 @@ bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI) {
}
// If we found some, do the transformation!
if (!UncondBranchPreds.empty()) {
if (!UncondBranchPreds.empty() && DupRet) {
while (!UncondBranchPreds.empty()) {
BasicBlock *Pred = UncondBranchPreds.pop_back_val();
DEBUG(dbgs() << "FOLDING: " << *BB
<< "INTO UNCOND BRANCH PRED: " << *Pred);
Instruction *UncondBranch = Pred->getTerminator();
// Clone the return and add it to the end of the predecessor.
Instruction *NewRet = RI->clone();
Pred->getInstList().push_back(NewRet);
// If the return instruction returns a value, and if the value was a
// PHI node in "BB", propagate the right value into the return.
for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
i != e; ++i)
if (PHINode *PN = dyn_cast<PHINode>(*i))
if (PN->getParent() == BB)
*i = PN->getIncomingValueForBlock(Pred);
// Update any PHI nodes in the returning block to realize that we no
// longer branch to them.
BB->removePredecessor(Pred);
UncondBranch->eraseFromParent();
(void)FoldReturnIntoUncondBranch(RI, BB, Pred);
}
// If we eliminated all predecessors of the block, delete the block now.

11
test/CodeGen/X86/loop-blocks.ll
View File

@ -70,6 +70,7 @@ exit:
; Same as slightly_more_involved, but block_a is now a CFG diamond with
; fallthrough edges which should be preserved.
; "callq block_a_merge_func" is tail duped.
; CHECK: yet_more_involved:
; CHECK: jmp .LBB2_1
@ -78,12 +79,12 @@ exit:
; CHECK-NEXT: callq bar99
; CHECK-NEXT: callq get
; CHECK-NEXT: cmpl $2999, %eax
; CHECK-NEXT: jg .LBB2_6
; CHECK-NEXT: callq block_a_true_func
; CHECK-NEXT: jmp .LBB2_7
; CHECK-NEXT: .LBB2_6:
; CHECK-NEXT: jle .LBB2_5
; CHECK-NEXT: callq block_a_false_func
; CHECK-NEXT: .LBB2_7:
; CHECK-NEXT: callq block_a_merge_func
; CHECK-NEXT: jmp .LBB2_1
; CHECK-NEXT: .LBB2_5:
; CHECK-NEXT: callq block_a_true_func
; CHECK-NEXT: callq block_a_merge_func
; CHECK-NEXT: .LBB2_1:
; CHECK-NEXT: callq body

10
test/Transforms/JumpThreading/and-and-cond.ll
View File

@ -1,14 +1,14 @@
; RUN: opt < %s -jump-threading -mem2reg -instcombine -simplifycfg -S | grep {ret i32 %v1}
; There should be no uncond branches left.
; RUN: opt < %s -jump-threading -mem2reg -instcombine -simplifycfg -S | not grep {br label}
; RUN: opt < %s -jump-threading -mem2reg -instcombine -simplifycfg -S | FileCheck %s
declare i32 @f1()
declare i32 @f2()
declare void @f3()
define i32 @test(i1 %cond, i1 %cond2, i1 %cond3) {
; CHECK: test
br i1 %cond, label %T1, label %F1
; CHECK-NOT: T1:
T1:
%v1 = call i32 @f1()
br label %Merge
@ -18,6 +18,10 @@ F1:
br label %Merge
Merge:
; CHECK: Merge:
; CHECK: %v1 = call i32 @f1()
; CHECK-NEXT: %D = and i1 %cond2, %cond3
; CHECK-NEXT: br i1 %D
%A = phi i1 [true, %T1], [false, %F1]
%B = phi i32 [%v1, %T1], [%v2, %F1]
%C = and i1 %A, %cond2

9
test/Transforms/JumpThreading/and-cond.ll
View File

@ -1,14 +1,14 @@
; RUN: opt < %s -jump-threading -mem2reg -instcombine -simplifycfg -S | grep {ret i32 %v1}
; There should be no uncond branches left.
; RUN: opt < %s -jump-threading -mem2reg -instcombine -simplifycfg -S | not grep {br label}
; RUN: opt < %s -jump-threading -mem2reg -instcombine -simplifycfg -S | FileCheck %s
declare i32 @f1()
declare i32 @f2()
declare void @f3()
define i32 @test(i1 %cond, i1 %cond2) {
; CHECK: test
br i1 %cond, label %T1, label %F1
; CHECK-NOT: T1
T1:
%v1 = call i32 @f1()
br label %Merge
@ -18,6 +18,9 @@ F1:
br label %Merge
Merge:
; CHECK: Merge:
; CHECK: %v1 = call i32 @f1()
; CHECK-NEXT: br i1 %cond2
%A = phi i1 [true, %T1], [false, %F1]
%B = phi i32 [%v1, %T1], [%v2, %F1]
%C = and i1 %A, %cond2

9
test/Transforms/JumpThreading/thread-loads.ll
View File

@ -1,4 +1,4 @@
; RUN: opt < %s -jump-threading -simplifycfg -S | grep {ret i32 1}
; RUN: opt < %s -jump-threading -S | FileCheck %s
; rdar://6402033
; Test that we can thread through the block with the partially redundant load (%2).
@ -6,12 +6,16 @@ target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f3
target triple = "i386-apple-darwin7"
define i32 @foo(i32* %P) nounwind {
; CHECK: foo
entry:
%0 = tail call i32 (...)* @f1() nounwind ; <i32> [#uses=1]
%1 = icmp eq i32 %0, 0 ; <i1> [#uses=1]
br i1 %1, label %bb1, label %bb
bb: ; preds = %entry
; CHECK: bb1.thread:
; CHECK: store
; CHECK: br label %bb3
store i32 42, i32* %P, align 4
br label %bb1
@ -26,6 +30,9 @@ bb2: ; preds = %bb1
ret i32 %res.0
bb3: ; preds = %bb1
; CHECK: bb3:
; CHECK: %res.01 = phi i32 [ 1, %bb1.thread ], [ 0, %bb1 ]
; CHECK: ret i32 %res.01
ret i32 %res.0
}

1
test/Transforms/SimplifyCFG/MagicPointer.ll
View File

@ -8,7 +8,6 @@
; CHECK: i64 2, label
; CHECK: i64 3, label
; CHECK: i64 4, label
; CHECK-NOT: br
; CHECK: }
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"

10
test/Transforms/SimplifyCFG/basictest.ll
View File

@ -25,16 +25,6 @@ define void @test3(i1 %T) {
}
define void @test4() {
br label %return
return:
ret void
; CHECK: @test4
; CHECK-NEXT: ret void
}
@test4g = global i8* blockaddress(@test4, %return)
; PR5795
define void @test5(i32 %A) {
switch i32 %A, label %return [

28
test/Transforms/SimplifyCFG/switch_create.ll
View File

@ -147,7 +147,7 @@ UnifiedReturnBlock: ; preds = %shortcirc_done.4, %shortcirc_next.4
; CHECK: i32 16, label %UnifiedReturnBlock
; CHECK: i32 17, label %UnifiedReturnBlock
; CHECK: i32 18, label %UnifiedReturnBlock
; CHECK: i32 19, label %switch.edge
; CHECK: i32 19, label %UnifiedReturnBlock
; CHECK: ]
}
@ -441,3 +441,29 @@ if.end:
; CHECK-NOT: switch
; CHECK: ret void
}
; PR8675
; rdar://5134905
define zeroext i1 @test16(i32 %x) nounwind {
entry:
; CHECK: @test16
; CHECK: switch i32 %x, label %lor.rhs [
; CHECK: i32 1, label %lor.end
; CHECK: i32 2, label %lor.end
; CHECK: i32 3, label %lor.end
; CHECK: ]
%cmp.i = icmp eq i32 %x, 1
br i1 %cmp.i, label %lor.end, label %lor.lhs.false
lor.lhs.false:
%cmp.i2 = icmp eq i32 %x, 2
br i1 %cmp.i2, label %lor.end, label %lor.rhs
lor.rhs:
%cmp.i1 = icmp eq i32 %x, 3
br label %lor.end
lor.end:
%0 = phi i1 [ true, %lor.lhs.false ], [ true, %entry ], [ %cmp.i1, %lor.rhs ]
ret i1 %0
}

14
test/Transforms/SimplifyCFG/switch_formation.dbg.ll
View File

@ -1,5 +1,4 @@
; RUN: opt < %s -simplifycfg -S | not grep br
; RUN: opt < %s -simplifycfg -S | FileCheck %s
%llvm.dbg.anchor.type = type { i32, i32 }
%llvm.dbg.compile_unit.type = type { i32, { }*, i32, i8*, i8*, i8*, i1, i1, i8* }
@ -13,7 +12,16 @@
declare void @llvm.dbg.stoppoint(i32, i32, { }*) nounwind
define i1 @_ZN4llvm11SetCondInst7classofEPKNS_11InstructionE({ i32, i32 }* %I) {
define i1 @t({ i32, i32 }* %I) {
; CHECK: t
; CHECK: switch i32 %tmp.2.i, label %shortcirc_next.4 [
; CHECK: i32 14, label %UnifiedReturnBlock
; CHECK: i32 15, label %UnifiedReturnBlock
; CHECK: i32 16, label %UnifiedReturnBlock
; CHECK: i32 17, label %UnifiedReturnBlock
; CHECK: i32 18, label %UnifiedReturnBlock
; CHECK: i32 19, label %UnifiedReturnBlock
; CHECK: ]
entry:
%tmp.1.i = getelementptr { i32, i32 }* %I, i64 0, i32 1 ; <i32*> [#uses=1]
%tmp.2.i = load i32* %tmp.1.i ; <i32> [#uses=6]