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Reverse order of the two branches at end of a basic block if it is profitable.
We branch to the successor with higher edge weight first.
Convert from
je LBB4_8 --> to outer loop
jmp LBB4_14 --> to inner loop
to
jne LBB4_14
jmp LBB4_8
PR12750
rdar: 11393714
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161018 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Manman Ren
parent
8b5704f958
commit
1123614317
@ -985,8 +985,22 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) {
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// boiler plate.
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Cond.clear();
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MachineBasicBlock *TBB = 0, *FBB = 0; // For AnalyzeBranch.
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if (!TII->AnalyzeBranch(*PrevBB, TBB, FBB, Cond))
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if (!TII->AnalyzeBranch(*PrevBB, TBB, FBB, Cond)) {
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// If PrevBB has a two-way branch, try to re-order the branches
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// such that we branch to the successor with higher weight first.
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if (TBB && !Cond.empty() && FBB &&
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MBPI->getEdgeWeight(PrevBB, FBB) > MBPI->getEdgeWeight(PrevBB, TBB) &&
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!TII->ReverseBranchCondition(Cond)) {
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DEBUG(dbgs() << "Reverse order of the two branches: "
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<< getBlockName(PrevBB) << "\n");
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DEBUG(dbgs() << " Edge weight: " << MBPI->getEdgeWeight(PrevBB, FBB)
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<< " vs " << MBPI->getEdgeWeight(PrevBB, TBB) << "\n");
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DebugLoc dl; // FIXME: this is nowhere
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TII->RemoveBranch(*PrevBB);
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TII->InsertBranch(*PrevBB, FBB, TBB, Cond, dl);
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}
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PrevBB->updateTerminator();
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}
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}
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// Fixup the last block.
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104
test/CodeGen/X86/reverse_branches.ll
Normal file
104
test/CodeGen/X86/reverse_branches.ll
Normal file
@ -0,0 +1,104 @@
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; RUN: llc -mtriple=x86_64-apple-darwin < %s | FileCheck %s
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@.str2 = private unnamed_addr constant [7 x i8] c"memchr\00", align 1
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@.str3 = private unnamed_addr constant [11 x i8] c"bsd_memchr\00", align 1
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@str4 = private unnamed_addr constant [5 x i8] c"Bug!\00"
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; Make sure at end of do.cond.i, we jump to do.body.i first to have a tighter
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; inner loop.
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define i32 @test_branches_order() uwtable ssp {
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; CHECK: test_branches_order:
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; CHECK: [[L0:LBB0_[0-9]+]]: ## %do.body.i
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; CHECK: je
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; CHECK: %do.cond.i
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; CHECK: jne [[L0]]
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; CHECK: jmp
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; CHECK: %exit
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entry:
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%strs = alloca [1000 x [1001 x i8]], align 16
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br label %for.cond
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for.cond:
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%j.0 = phi i32 [ 0, %entry ], [ %inc10, %for.inc9 ]
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%cmp = icmp slt i32 %j.0, 1000
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br i1 %cmp, label %for.cond1, label %for.end11
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for.cond1:
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%indvars.iv50 = phi i64 [ %indvars.iv.next51, %for.body3 ], [ 0, %for.cond ]
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%0 = trunc i64 %indvars.iv50 to i32
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%cmp2 = icmp slt i32 %0, 1000
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br i1 %cmp2, label %for.body3, label %for.inc9
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for.body3:
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%arraydecay = getelementptr inbounds [1000 x [1001 x i8]]* %strs, i64 0, i64 %indvars.iv50, i64 0
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%call = call i8* @memchr(i8* %arraydecay, i32 120, i64 1000)
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%add.ptr = getelementptr inbounds [1000 x [1001 x i8]]* %strs, i64 0, i64 %indvars.iv50, i64 %indvars.iv50
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%cmp7 = icmp eq i8* %call, %add.ptr
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%indvars.iv.next51 = add i64 %indvars.iv50, 1
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br i1 %cmp7, label %for.cond1, label %if.then
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if.then:
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%puts = call i32 @puts(i8* getelementptr inbounds ([5 x i8]* @str4, i64 0, i64 0))
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call void @exit(i32 1) noreturn
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unreachable
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for.inc9:
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%inc10 = add nsw i32 %j.0, 1
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br label %for.cond
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for.end11:
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%puts42 = call i32 @puts(i8* getelementptr inbounds ([7 x i8]* @.str2, i64 0, i64 0))
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br label %for.cond14
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for.cond14:
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%j13.0 = phi i32 [ 0, %for.end11 ], [ %inc39, %for.inc38 ]
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%cmp15 = icmp slt i32 %j13.0, 1000
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br i1 %cmp15, label %for.cond18, label %for.end40
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for.cond18:
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%indvars.iv = phi i64 [ %indvars.iv.next, %exit ], [ 0, %for.cond14 ]
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%1 = trunc i64 %indvars.iv to i32
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%cmp19 = icmp slt i32 %1, 1000
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br i1 %cmp19, label %for.body20, label %for.inc38
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for.body20:
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%arraydecay24 = getelementptr inbounds [1000 x [1001 x i8]]* %strs, i64 0, i64 %indvars.iv, i64 0
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br label %do.body.i
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do.body.i:
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%n.addr.0.i = phi i64 [ %dec.i, %do.cond.i ], [ 1000, %for.body20 ]
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%p.0.i = phi i8* [ %incdec.ptr.i, %do.cond.i ], [ %arraydecay24, %for.body20 ]
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%2 = load i8* %p.0.i, align 1
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%cmp3.i = icmp eq i8 %2, 120
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br i1 %cmp3.i, label %exit, label %do.cond.i
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do.cond.i:
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%incdec.ptr.i = getelementptr inbounds i8* %p.0.i, i64 1
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%dec.i = add i64 %n.addr.0.i, -1
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%cmp5.i = icmp eq i64 %dec.i, 0
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br i1 %cmp5.i, label %if.then32, label %do.body.i
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exit:
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%add.ptr30 = getelementptr inbounds [1000 x [1001 x i8]]* %strs, i64 0, i64 %indvars.iv, i64 %indvars.iv
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%cmp31 = icmp eq i8* %p.0.i, %add.ptr30
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%indvars.iv.next = add i64 %indvars.iv, 1
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br i1 %cmp31, label %for.cond18, label %if.then32
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if.then32:
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%puts43 = call i32 @puts(i8* getelementptr inbounds ([5 x i8]* @str4, i64 0, i64 0))
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call void @exit(i32 1) noreturn
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unreachable
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for.inc38:
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%inc39 = add nsw i32 %j13.0, 1
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br label %for.cond14
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for.end40:
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%puts44 = call i32 @puts(i8* getelementptr inbounds ([11 x i8]* @.str3, i64 0, i64 0))
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ret i32 0
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}
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declare i8* @memchr(i8*, i32, i64) nounwind readonly
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declare void @exit(i32) noreturn
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declare i32 @puts(i8* nocapture) nounwind
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