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[LoopDeletion] Emit a remark when a dead loop is deleted
This emits a remark when LoopDeletion deletes a dead loop, using the source location of the loop's header. There are currently two reasons for removing the loop: invariant loop or loop that never executes. Differential Revision: https://reviews.llvm.org/D83113
This commit is contained in:
Francis Visoiu Mistrih
parent
dae9803e4d
commit
a210f22919
@ -19,6 +19,7 @@
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#include "llvm/Analysis/GlobalsModRef.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/MemorySSA.h"
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#include "llvm/Analysis/OptimizationRemarkEmitter.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/PatternMatch.h"
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#include "llvm/InitializePasses.h"
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@ -136,7 +137,8 @@ static bool isLoopNeverExecuted(Loop *L) {
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/// instructions out of the loop.
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static LoopDeletionResult deleteLoopIfDead(Loop *L, DominatorTree &DT,
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ScalarEvolution &SE, LoopInfo &LI,
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MemorySSA *MSSA) {
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MemorySSA *MSSA,
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OptimizationRemarkEmitter &ORE) {
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assert(L->isLCSSAForm(DT) && "Expected LCSSA!");
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// We can only remove the loop if there is a preheader that we can branch from
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@ -166,6 +168,11 @@ static LoopDeletionResult deleteLoopIfDead(Loop *L, DominatorTree &DT,
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std::fill(P.incoming_values().begin(), P.incoming_values().end(),
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UndefValue::get(P.getType()));
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}
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ORE.emit([&]() {
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return OptimizationRemark(DEBUG_TYPE, "NeverExecutes", L->getStartLoc(),
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L->getHeader())
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<< "Loop deleted because it never executes";
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});
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deleteDeadLoop(L, &DT, &SE, &LI, MSSA);
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++NumDeleted;
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return LoopDeletionResult::Deleted;
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@ -202,6 +209,11 @@ static LoopDeletionResult deleteLoopIfDead(Loop *L, DominatorTree &DT,
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}
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LLVM_DEBUG(dbgs() << "Loop is invariant, delete it!");
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ORE.emit([&]() {
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return OptimizationRemark(DEBUG_TYPE, "Invariant", L->getStartLoc(),
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L->getHeader())
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<< "Loop deleted because it is invariant";
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});
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deleteDeadLoop(L, &DT, &SE, &LI, MSSA);
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++NumDeleted;
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@ -215,7 +227,11 @@ PreservedAnalyses LoopDeletionPass::run(Loop &L, LoopAnalysisManager &AM,
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LLVM_DEBUG(dbgs() << "Analyzing Loop for deletion: ");
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LLVM_DEBUG(L.dump());
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std::string LoopName = std::string(L.getName());
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auto Result = deleteLoopIfDead(&L, AR.DT, AR.SE, AR.LI, AR.MSSA);
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// For the new PM, we can't use OptimizationRemarkEmitter as an analysis
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// pass. Function analyses need to be preserved across loop transformations
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// but ORE cannot be preserved (see comment before the pass definition).
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OptimizationRemarkEmitter ORE(L.getHeader()->getParent());
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auto Result = deleteLoopIfDead(&L, AR.DT, AR.SE, AR.LI, AR.MSSA, ORE);
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if (Result == LoopDeletionResult::Unmodified)
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return PreservedAnalyses::all();
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@ -265,11 +281,15 @@ bool LoopDeletionLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) {
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MemorySSA *MSSA = nullptr;
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if (MSSAAnalysis)
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MSSA = &MSSAAnalysis->getMSSA();
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// For the old PM, we can't use OptimizationRemarkEmitter as an analysis
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// pass. Function analyses need to be preserved across loop transformations
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// but ORE cannot be preserved (see comment before the pass definition).
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OptimizationRemarkEmitter ORE(L->getHeader()->getParent());
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LLVM_DEBUG(dbgs() << "Analyzing Loop for deletion: ");
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LLVM_DEBUG(L->dump());
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LoopDeletionResult Result = deleteLoopIfDead(L, DT, SE, LI, MSSA);
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LoopDeletionResult Result = deleteLoopIfDead(L, DT, SE, LI, MSSA, ORE);
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if (Result == LoopDeletionResult::Deleted)
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LPM.markLoopAsDeleted(*L);
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37
test/Transforms/LoopDeletion/basic-remark.ll
Normal file
37
test/Transforms/LoopDeletion/basic-remark.ll
Normal file
@ -0,0 +1,37 @@
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; RUN: opt -loop-deletion %s -o /dev/null --pass-remarks-output=%t --pass-remarks-filter=loop-delete
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; RUN: cat %t | FileCheck %s
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; Check that we use the right debug location: the loop header.
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; CHECK: --- !Passed
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; CHECK-NEXT: Pass: loop-delete
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; CHECK-NEXT: Name: Invariant
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; CHECK-NEXT: DebugLoc: { File: loop.c, Line: 2, Column: 3 }
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; CHECK-NEXT: Function: main
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; CHECK-NEXT: Args:
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; CHECK-NEXT: - String: Loop deleted because it is invariant
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; CHECK-NEXT: ...
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define i32 @main() local_unnamed_addr #0 {
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entry:
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br label %for.cond, !dbg !9
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for.cond:
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%i.0 = phi i32 [ 0, %entry ], [ %inc, %for.cond ]
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%cmp = icmp ult i32 %i.0, 1000
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%inc = add nuw nsw i32 %i.0, 1
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br i1 %cmp, label %for.cond, label %for.cond.cleanup
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for.cond.cleanup:
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ret i32 0
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}
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!3}
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!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "", isOptimized: true, runtimeVersion: 0, emissionKind: NoDebug, enums: !2, nameTableKind: None, sysroot: "/")
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!1 = !DIFile(filename: "loop.c", directory: "")
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!2 = !{}
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!3 = !{i32 2, !"Debug Info Version", i32 3}
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!6 = distinct !DISubprogram(name: "main", scope: !7, file: !7, line: 1, type: !8, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
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!7 = !DIFile(filename: "loop.c", directory: "")
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!8 = !DISubroutineType(types: !2)
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!9 = !DILocation(line: 2, column: 3, scope: !6)
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@ -1,4 +1,5 @@
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; RUN: opt < %s -loop-deletion -verify-dom-info -S | FileCheck %s
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; RUN: opt < %s -loop-deletion -verify-dom-info --pass-remarks-output=%t --pass-remarks-filter=loop-delete -S | FileCheck %s
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; RUN: cat %t | FileCheck %s --check-prefix=REMARKS
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; Checking that we can delete loops that are never executed.
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; We do not change the constant conditional branch statement (where the not-taken target
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@ -10,6 +11,8 @@ define void @test1(i64 %n, i64 %m) nounwind {
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; CHECK-LABEL: entry:
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; CHECK-NEXT: br i1 true, label %return, label %bb.preheader
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; CHECK-NOT: bb:
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; REMARKS-LABEL: Function: test1
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; REMARKS: Loop deleted because it never executes
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entry:
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br i1 true, label %return, label %bb
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@ -63,6 +66,8 @@ define i64 @test3(i64 %n, i64 %m, i64 %maybe_zero) nounwind {
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; CHECK-LABEL: return:
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; CHECK-NEXT: %x.lcssa = phi i64 [ 20, %entry ], [ %x.lcssa.ph, %return.loopexit ]
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; CHECK-NEXT: ret i64 %x.lcssa
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; REMARKS-LABEL: Function: test3
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; REMARKS: Loop deleted because it never executes
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entry:
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br i1 false, label %bb, label %return
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@ -121,6 +126,8 @@ define void @test5(i64 %n, i64 %m, i1 %cond) nounwind {
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; CHECK-LABEL: looppred2:
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; CHECK-NEXT: br i1 true, label %return, label %bb.preheader
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; CHECK-NOT: bb:
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; REMARKS-LABEL: Function: test5
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; REMARKS: Loop deleted because it never executes
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entry:
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br i1 %cond, label %looppred1, label %looppred2
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@ -179,6 +186,8 @@ define i64 @test7(i64 %n) {
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; CHECK-LABEL: L1Latch:
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; CHECK-NEXT: %y = phi i64 [ %y.next, %L1 ], [ %y.L2.lcssa, %L1Latch.loopexit ]
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; CHECK: br i1 %cond2, label %exit, label %L1
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; REMARKS-LABEL: Function: test7
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; REMARKS: Loop deleted because it never executes
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entry:
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br label %L1
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@ -213,6 +222,8 @@ define void @test8(i64 %n) {
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; CHECK-NEXT: br label %exit
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; CHECK-LABEL: exit:
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; CHECK-NEXT: ret void
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; REMARKS-LABEL: Function: test8
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; REMARKS: Loop deleted because it never executes
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entry:
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br label %L1
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@ -246,6 +257,8 @@ define void @test9(i64 %n) {
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; CHECK-NEXT: br label %L3
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; CHECK-LABEL: L3:
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; CHECK: br i1 %cond2, label %L3, label %L1.loopexit
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; REMARKS-LABEL: Function: test9
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; REMARKS: Loop deleted because it never executes
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entry:
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br label %L1
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@ -311,6 +324,12 @@ define void @test11(i64 %n) {
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; CHECK-NEXT: br label %exit
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; CHECK-LABEL: exit:
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; CHECK-NEXT: ret void
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; REMARKS-LABEL: Function: test11
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; REMARKS: Loop deleted because it is invariant
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; REMARKS-LABEL: Function: test11
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; REMARKS: Loop deleted because it never executes
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; REMARKS-LABEL: Function: test11
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; REMARKS: Loop deleted because it is invariant
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entry:
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br label %L1
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@ -345,6 +364,8 @@ define i64 @test12(i64 %n){
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; CHECK-LABEL: exit:
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; CHECK-NEXT: %y.phi = phi i64 [ undef, %L1.preheader ]
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; CHECK-NEXT: ret i64 %y.phi
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; REMARKS-LABEL: Function: test12
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; REMARKS: Loop deleted because it never executes
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entry:
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br i1 true, label %exit1, label %L1
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@ -380,6 +401,8 @@ define i64 @test13(i64 %n) {
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; CHECK-LABEL: exit:
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; CHECK-NEXT: %y.phi = phi i64 [ undef, %L1.preheader ]
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; CHECK-NEXT: ret i64 %y.phi
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; REMARKS-LABEL: Function: test13
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; REMARKS: Loop deleted because it never executes
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entry:
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br i1 true, label %exit1, label %L1
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