forked from OSchip/llvm-project
[ShrinkWrapping] Do not choose restore point inside loops.
The post-dominance property is not sufficient to guarantee that a restore point
inside a loop is safe.
E.g.,
while(1) {
Save
Restore
if (...)
break;
use/def CSRs
}
All the uses/defs of CSRs are dominated by Save and post-dominated
by Restore. However, the CSRs uses are still reachable after
Restore and before Save are executed.
This fixes PR25824
llvm-svn: 255613
This commit is contained in:
Quentin Colombet
parent
e3d7b58ba6
commit
b82786e0ff
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@ -319,7 +319,24 @@ void ShrinkWrap::updateSaveRestorePoints(MachineBasicBlock &MBB,
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while (Save && Restore &&
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(!(SaveDominatesRestore = MDT->dominates(Save, Restore)) ||
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!(RestorePostDominatesSave = MPDT->dominates(Restore, Save)) ||
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MLI->getLoopFor(Save) != MLI->getLoopFor(Restore))) {
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// Post-dominance is not enough in loops to ensure that all uses/defs
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// are after the prologue and before the epilogue at runtime.
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// E.g.,
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// while(1) {
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// Save
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// Restore
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// if (...)
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// break;
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// use/def CSRs
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// }
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// All the uses/defs of CSRs are dominated by Save and post-dominated
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// by Restore. However, the CSRs uses are still reachable after
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// Restore and before Save are executed.
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//
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// For now, just push the restore/save points outside of loops.
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// FIXME: Refine the criteria to still find interesting cases
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// for loops.
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MLI->getLoopFor(Save) || MLI->getLoopFor(Restore))) {
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// Fix (A).
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if (!SaveDominatesRestore) {
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Save = MDT->findNearestCommonDominator(Save, Restore);
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@ -330,8 +347,8 @@ void ShrinkWrap::updateSaveRestorePoints(MachineBasicBlock &MBB,
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Restore = MPDT->findNearestCommonDominator(Restore, Save);
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// Fix (C).
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if (Save && Restore && Save != Restore &&
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MLI->getLoopFor(Save) != MLI->getLoopFor(Restore)) {
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if (Save && Restore &&
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(MLI->getLoopFor(Save) || MLI->getLoopFor(Restore))) {
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if (MLI->getLoopDepth(Save) > MLI->getLoopDepth(Restore)) {
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// Push Save outside of this loop if immediate dominator is different
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// from save block. If immediate dominator is not different, bail out.
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@ -342,8 +359,7 @@ void ShrinkWrap::updateSaveRestorePoints(MachineBasicBlock &MBB,
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Save = nullptr;
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break;
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}
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}
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else {
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} else {
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// If the loop does not exit, there is no point in looking
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// for a post-dominator outside the loop.
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SmallVector<MachineBasicBlock*, 4> ExitBlocks;
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@ -0,0 +1,142 @@
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; RUN: llc %s -o - -enable-shrink-wrap=true | FileCheck %s --check-prefix=CHECK --check-prefix=ENABLE
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; RUN: llc %s -o - -enable-shrink-wrap=false | FileCheck %s --check-prefix=CHECK --check-prefix=DISABLE
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; We cannot merge this test with the main test for shrink-wrapping, because
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; the code path we want to exerce is not taken with ios lowering.
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target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n8:16:32-S64"
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target triple = "armv7--linux-gnueabi"
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@skip = internal unnamed_addr constant [2 x i8] c"\01\01", align 1
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; Check that we do not restore the before having used the saved CSRs.
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; This happened because of a bad use of the post-dominance property.
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; The exit block of the loop happens to also lead to defs/uses of CSRs.
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; It also post-dominates the loop body and we use to generate invalid
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; restore sequence. I.e., we restored too early.
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;
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; CHECK-LABEL: wrongUseOfPostDominate:
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;
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; The prologue is the first thing happening in the function
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; without shrink-wrapping.
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; DISABLE: push
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;
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; CHECK: cmp r1, #0
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;
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; With shrink-wrapping, we branch to a pre-header, where the prologue
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; is located.
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; ENABLE-NEXT: blt [[LOOP_PREHEADER:[.a-zA-Z0-9_]+]]
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; Without shrink-wrapping, we go straight into the loop.
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; DISABLE-NEXT: blt [[LOOP_HEADER:[.a-zA-Z0-9_]+]]
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;
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; CHECK: @ %if.end29
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; DISABLE-NEXT: pop
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; ENABLE-NEXT: bx lr
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;
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; ENABLE: [[LOOP_PREHEADER]]
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; ENABLE: push
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; We must not find a pop here, otherwise that means we are in the loop
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; and are restoring before using the saved CSRs.
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; ENABLE-NOT: pop
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; ENALBE-NEXT: [[LOOP_HEADER:[.a-zA-Z0-9_]+]]: @ %while.cond2.outer
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;
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; DISABLE: [[LOOP_HEADER]]: @ %while.cond2.outer
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;
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; ENABLE-NOT: pop
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;
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; CHECK: @ %while.cond2
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; CHECK: add
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; CHECK-NEXT: cmp r{{[0-1]+}}, #1
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; Set the return value.
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; CHECK-NEXT: moveq r0,
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; CHECK-NEXT: popeq
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;
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; Use the back edge to check we get the label of the loop right.
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; This is to make sure we check the right loop pattern.
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; CHECK: @ %while.body24.land.rhs14_crit_edge
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; CHECK: cmp r{{[0-9]+}}, #192
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; CHECK-NEXT bhs [[LOOP_HEADER]]
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define fastcc i8* @wrongUseOfPostDominate(i8* readonly %s, i32 %off, i8* readnone %lim) {
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entry:
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%cmp = icmp sgt i32 %off, -1
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br i1 %cmp, label %while.cond.preheader, label %while.cond2.outer
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while.cond.preheader: ; preds = %entry
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%tobool4 = icmp ne i32 %off, 0
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%cmp15 = icmp ult i8* %s, %lim
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%sel66 = and i1 %tobool4, %cmp15
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br i1 %sel66, label %while.body, label %if.end29
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while.body: ; preds = %while.body, %while.cond.preheader
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%s.addr.08 = phi i8* [ %add.ptr, %while.body ], [ %s, %while.cond.preheader ]
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%off.addr.07 = phi i32 [ %dec, %while.body ], [ %off, %while.cond.preheader ]
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%dec = add nsw i32 %off.addr.07, -1
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%tmp = load i8, i8* %s.addr.08, align 1, !tbaa !2
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%idxprom = zext i8 %tmp to i32
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%arrayidx = getelementptr inbounds [2 x i8], [2 x i8]* @skip, i32 0, i32 %idxprom
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%tmp1 = load i8, i8* %arrayidx, align 1, !tbaa !2
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%conv = zext i8 %tmp1 to i32
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%add.ptr = getelementptr inbounds i8, i8* %s.addr.08, i32 %conv
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%tobool = icmp ne i32 %off.addr.07, 1
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%cmp1 = icmp ult i8* %add.ptr, %lim
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%sel6 = and i1 %tobool, %cmp1
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br i1 %sel6, label %while.body, label %if.end29
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while.cond2.outer: ; preds = %while.body24.land.rhs14_crit_edge, %while.body24, %land.rhs14.preheader, %if.then7, %entry
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%off.addr.1.ph = phi i32 [ %off, %entry ], [ %inc, %land.rhs14.preheader ], [ %inc, %if.then7 ], [ %inc, %while.body24.land.rhs14_crit_edge ], [ %inc, %while.body24 ]
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%s.addr.1.ph = phi i8* [ %s, %entry ], [ %incdec.ptr, %land.rhs14.preheader ], [ %incdec.ptr, %if.then7 ], [ %lsr.iv, %while.body24.land.rhs14_crit_edge ], [ %lsr.iv, %while.body24 ]
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br label %while.cond2
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while.cond2: ; preds = %while.body4, %while.cond2.outer
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%off.addr.1 = phi i32 [ %inc, %while.body4 ], [ %off.addr.1.ph, %while.cond2.outer ]
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%inc = add nsw i32 %off.addr.1, 1
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%tobool3 = icmp eq i32 %off.addr.1, 0
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br i1 %tobool3, label %if.end29, label %while.body4
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while.body4: ; preds = %while.cond2
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%tmp2 = icmp ugt i8* %s.addr.1.ph, %lim
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br i1 %tmp2, label %if.then7, label %while.cond2
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if.then7: ; preds = %while.body4
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%incdec.ptr = getelementptr inbounds i8, i8* %s.addr.1.ph, i32 -1
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%tmp3 = load i8, i8* %incdec.ptr, align 1, !tbaa !2
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%conv1525 = zext i8 %tmp3 to i32
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%tobool9 = icmp slt i8 %tmp3, 0
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%cmp129 = icmp ugt i8* %incdec.ptr, %lim
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%or.cond13 = and i1 %tobool9, %cmp129
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br i1 %or.cond13, label %land.rhs14.preheader, label %while.cond2.outer
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land.rhs14.preheader: ; preds = %if.then7
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%cmp1624 = icmp slt i8 %tmp3, 0
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%cmp2026 = icmp ult i32 %conv1525, 192
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%or.cond27 = and i1 %cmp1624, %cmp2026
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br i1 %or.cond27, label %while.body24.preheader, label %while.cond2.outer
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while.body24.preheader: ; preds = %land.rhs14.preheader
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%scevgep = getelementptr i8, i8* %s.addr.1.ph, i32 -2
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br label %while.body24
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while.body24: ; preds = %while.body24.land.rhs14_crit_edge, %while.body24.preheader
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%lsr.iv = phi i8* [ %scevgep, %while.body24.preheader ], [ %scevgep34, %while.body24.land.rhs14_crit_edge ]
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%cmp12 = icmp ugt i8* %lsr.iv, %lim
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br i1 %cmp12, label %while.body24.land.rhs14_crit_edge, label %while.cond2.outer
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while.body24.land.rhs14_crit_edge: ; preds = %while.body24
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%.pre = load i8, i8* %lsr.iv, align 1, !tbaa !2
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%cmp16 = icmp slt i8 %.pre, 0
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%conv15 = zext i8 %.pre to i32
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%cmp20 = icmp ult i32 %conv15, 192
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%or.cond = and i1 %cmp16, %cmp20
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%scevgep34 = getelementptr i8, i8* %lsr.iv, i32 -1
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br i1 %or.cond, label %while.body24, label %while.cond2.outer
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if.end29: ; preds = %while.cond2, %while.body, %while.cond.preheader
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%s.addr.3 = phi i8* [ %s, %while.cond.preheader ], [ %add.ptr, %while.body ], [ %s.addr.1.ph, %while.cond2 ]
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ret i8* %s.addr.3
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}
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!llvm.module.flags = !{!0, !1}
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!0 = !{i32 1, !"wchar_size", i32 4}
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!1 = !{i32 1, !"min_enum_size", i32 4}
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!2 = !{!3, !3, i64 0}
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!3 = !{!"omnipotent char", !4, i64 0}
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!4 = !{!"Simple C/C++ TBAA"}
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