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Make tail merging handle blocks with repeated predecessors correctly, and

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remove RemoveDuplicateSuccessor, as it is no longer necessary, and because
it breaks assumptions made in
MachineBasicBlock::isOnlyReachableByFallthrough.

Convert test/CodeGen/X86/omit-label.ll to FileCheck and add a testcase
for PR4732.

test/CodeGen/Thumb2/thumb2-ifcvt2.ll sees a diff with this commit due to
it being bugpoint-reduced to the point where it doesn't matter what the
condition for the branch is.

Add some more interesting code to
test/CodeGen/X86/2009-08-06-branchfolder-crash.ll, which is the testcase
that originally motivated the RemoveDuplicateSuccessor code, to help
verify that the original problem isn't being re-broken.

llvm-svn: 79338
This commit is contained in:
Dan Gohman 2009-08-18 15:18:18 +00:00
parent 0b1af29372
commit 5022dd9cc9
4 changed files with 93 additions and 28 deletions
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29
lib/CodeGen/BranchFolding.cpp
View File

@ -700,6 +700,7 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
if (I->pred_size() >= 2 && I->pred_size() < TailMergeThreshold) {
SmallPtrSet<MachineBasicBlock *, 8> UniquePreds;
MachineBasicBlock *IBB = I;
MachineBasicBlock *PredBB = prior(I);
MergePotentials.clear();
@ -710,6 +711,9 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
// Skip blocks that loop to themselves, can't tail merge these.
if (PBB==IBB)
continue;
// Visit each predecessor only once.
if (!UniquePreds.insert(PBB))
continue;
MachineBasicBlock *TBB = 0, *FBB = 0;
SmallVector<MachineOperand, 4> Cond;
if (!TII->AnalyzeBranch(*PBB, TBB, FBB, Cond, true)) {
@ -850,27 +854,6 @@ bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB) {
return CanFallThrough(CurBB, CurUnAnalyzable, TBB, FBB, Cond);
}
/// RemoveDuplicateSuccessor - make sure block Pred has at most one
/// successor edge leading to Succ. This is only called in one place,
/// but Chris prefers that it be a separate function.
static void RemoveDuplicateSuccessor(MachineBasicBlock *Pred,
MachineBasicBlock *Succ) {
MachineBasicBlock::succ_iterator SI = Pred->succ_begin();
bool found = false;
while (SI != Pred->succ_end()) {
if (*SI == Succ) {
if (!found) {
found = true;
++SI;
} else {
SI = Pred->removeSuccessor(SI);
}
} else {
++SI;
}
}
}
/// IsBetterFallthrough - Return true if it would be clearly better to
/// fall-through to MBB1 than to fall through into MBB2. This has to return
/// a strict ordering, returning true for both (MBB1,MBB2) and (MBB2,MBB1) will
@ -914,10 +897,6 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
while (!MBB->pred_empty()) {
MachineBasicBlock *Pred = *(MBB->pred_end()-1);
Pred->ReplaceUsesOfBlockWith(MBB, FallThrough);
// If this resulted in a predecessor with true and false edges
// both going to the fallthrough block, clean up;
// BranchFolding doesn't like this.
RemoveDuplicateSuccessor(Pred, FallThrough);
}
// If MBB was the target of a jump table, update jump tables to go to the
// fallthrough instead.

2
test/CodeGen/Thumb2/thumb2-ifcvt2.ll
View File

@ -82,7 +82,7 @@ define fastcc void @t2() nounwind {
entry:
; CHECK: t2:
; CHECK: cmp r0, #0
; CHECK: bne.n
; CHECK: beq.n
br i1 undef, label %bb.i.i3, label %growMapping.exit
bb.i.i3: ; preds = %entry

52
test/CodeGen/X86/2009-08-06-branchfolder-crash.ll
View File

@ -88,3 +88,55 @@ for.inc: ; preds = %for.inc, %lor.end.i, %lor.rhs.i, %land.lhs.true3.i
}
declare i32 @safe()
define i32 @func_35(i8 signext %p_35) nounwind readonly {
entry:
%tobool = icmp eq i8 %p_35, 0 ; <i1> [#uses=1]
br i1 %tobool, label %lor.lhs.false, label %if.then
lor.lhs.false: ; preds = %entry
%tmp1 = load i8* @g_3 ; <i8> [#uses=1]
%tobool3 = icmp eq i8 %tmp1, 0 ; <i1> [#uses=1]
br i1 %tobool3, label %return, label %if.then
if.then: ; preds = %lor.lhs.false, %entry
%tmp4 = load i8* @g_3 ; <i8> [#uses=1]
%conv5 = sext i8 %tmp4 to i32 ; <i32> [#uses=1]
ret i32 %conv5
return: ; preds = %lor.lhs.false
ret i32 0
}
define void @bar(i32 %p_5) noreturn nounwind {
entry:
%cmp = icmp sgt i32 %p_5, 0 ; <i1> [#uses=2]
%call = tail call i32 @safe() nounwind ; <i32> [#uses=1]
%conv1 = trunc i32 %call to i8 ; <i8> [#uses=3]
%tobool.i = xor i1 %cmp, true ; <i1> [#uses=3]
%cmp.i = icmp sgt i8 %conv1, 0 ; <i1> [#uses=3]
%or.cond.i = or i1 %cmp.i, %tobool.i ; <i1> [#uses=1]
br i1 %or.cond.i, label %lor.rhs.i, label %land.lhs.true3.i
land.lhs.true3.i: ; preds = %entry
%xor = zext i1 %cmp to i32 ; <i32> [#uses=1]
%conv5.i = sext i8 %conv1 to i32 ; <i32> [#uses=1]
%cmp7.i = icmp slt i32 %conv5.i, %xor ; <i1> [#uses=1]
%cmp7.i.not = xor i1 %cmp7.i, true ; <i1> [#uses=1]
%or.cond23.i = and i1 %cmp.i, %tobool.i ; <i1> [#uses=1]
%or.cond = and i1 %cmp7.i.not, %or.cond23.i ; <i1> [#uses=1]
br i1 %or.cond, label %lor.end.i, label %for.inc
lor.rhs.i: ; preds = %entry
%or.cond23.i.old = and i1 %cmp.i, %tobool.i ; <i1> [#uses=1]
br i1 %or.cond23.i.old, label %lor.end.i, label %for.inc
lor.end.i: ; preds = %lor.rhs.i, %land.lhs.true3.i
%tobool19.i = icmp eq i8 %conv1, 0 ; <i1> [#uses=0]
br label %for.inc
for.inc: ; preds = %for.inc, %lor.end.i, %lor.rhs.i, %land.lhs.true3.i
br label %for.inc
}
declare i32 @safe()

38
test/CodeGen/X86/omit-label.ll
View File

@ -1,7 +1,11 @@
; RUN: llvm-as < %s | llc -march=x86-64 | grep BB1_1:
; RUN: llvm-as < %s | llc -march=x86-64 -asm-verbose=false | FileCheck %s
; PR4126
; PR4732
; Don't omit this label's definition.
; Don't omit these labels' definitions.
; CHECK: bux:
; CHECK: .LBB1_1:
define void @bux(i32 %p_53) nounwind optsize {
entry:
@ -21,3 +25,33 @@ bb3: ; preds = %bb.i, %entry
}
declare i32 @baz(...)
; Don't omit this label in the assembly output.
; CHECK: int321:
; CHECK: jne .LBB2_1
; CHECK: jle .LBB2_1
; CHECK: .LBB2_1:
define void @int321(i8 signext %p_103, i32 %uint8p_104) nounwind readnone {
entry:
%tobool = icmp eq i8 %p_103, 0 ; <i1> [#uses=1]
%cmp.i = icmp sgt i8 %p_103, 0 ; <i1> [#uses=1]
%or.cond = and i1 %tobool, %cmp.i ; <i1> [#uses=1]
br i1 %or.cond, label %land.end.i, label %for.cond.preheader
land.end.i: ; preds = %entry
%conv3.i = sext i8 %p_103 to i32 ; <i32> [#uses=1]
%div.i = sdiv i32 1, %conv3.i ; <i32> [#uses=1]
%tobool.i = icmp eq i32 %div.i, -2147483647 ; <i1> [#uses=0]
br label %for.cond.preheader
for.cond.preheader: ; preds = %land.end.i, %entry
%cmp = icmp sgt i8 %p_103, 1 ; <i1> [#uses=1]
br i1 %cmp, label %for.end.split, label %for.cond
for.cond: ; preds = %for.cond.preheader, %for.cond
br label %for.cond
for.end.split: ; preds = %for.cond.preheader
ret void
}