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Specify branch probabilities for callbr dests

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Summary:
callbr's indirect branches aren't expected to be taken, so reduce their
probabilities to 0 while increasing the default destination to 1. This
allows some code improvements through block placement.

Reviewers: nickdesaulniers

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D72656
This commit is contained in:
Bill Wendling 2020-03-11 17:07:02 -07:00
parent 158f416572
commit 7ce3e3e17b
5 changed files with 29 additions and 31 deletions
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4
lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
View File

@ -2867,10 +2867,10 @@ void SelectionDAGBuilder::visitCallBr(const CallBrInst &I) {
Return->setInlineAsmBrDefaultTarget();
// Update successor info.
addSuccessorWithProb(CallBrMBB, Return);
addSuccessorWithProb(CallBrMBB, Return, BranchProbability::getOne());
for (unsigned i = 0, e = I.getNumIndirectDests(); i < e; ++i) {
MachineBasicBlock *Target = FuncInfo.MBBMap[I.getIndirectDest(i)];
addSuccessorWithProb(CallBrMBB, Target);
addSuccessorWithProb(CallBrMBB, Target, BranchProbability::getZero());
CallBrMBB->addInlineAsmBrIndirectTarget(Target);
}
CallBrMBB->normalizeSuccProbs();

12
test/CodeGen/AArch64/callbr-asm-label.ll
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@ -6,18 +6,18 @@ define i32 @test1() {
; CHECK-LABEL: test1:
; CHECK: .word b
; CHECK-NEXT: .word .Ltmp0
; CHECK-LABEL: .LBB0_1: // %cleanup
; CHECK-LABEL: .Ltmp0:
; CHECK-LABEL: .LBB0_1: // %l_yes
; CHECK-LABEL: .LBB0_2: // %cleanup
; CHECK-LABEL: .LBB0_2: // %indirect
entry:
callbr void asm sideeffect "1:\0A\09.word b, ${0:l}\0A\09", "X"(i8* blockaddress(@test1, %l_yes))
to label %cleanup [label %l_yes]
callbr void asm sideeffect "1:\0A\09.word b, ${0:l}\0A\09", "X"(i8* blockaddress(@test1, %indirect))
to label %cleanup [label %indirect]
l_yes:
indirect:
br label %cleanup
cleanup:
%retval.0 = phi i32 [ 1, %l_yes ], [ 0, %entry ]
%retval.0 = phi i32 [ 1, %indirect ], [ 0, %entry ]
ret i32 %retval.0
}

4
test/CodeGen/AArch64/callbr-asm-obj-file.ll
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@ -41,10 +41,10 @@ declare dso_local i32 @g(...) local_unnamed_addr
declare dso_local i32 @i(...) local_unnamed_addr
; CHECK-LABEL: <test2>:
; CHECK: bl #0 <test2+0x10>
; CHECK: bl #0 <test2+0x18>
; CHECK-LABEL: <$d.5>:
; CHECK-LABEL: <$x.6>:
; CHECK-NEXT: b #16 <$x.8+0x4>
; CHECK-NEXT: b #-20 <test2+0x18>
define hidden i32 @test2() local_unnamed_addr {
%1 = load i32, i32* @l, align 4
%2 = icmp eq i32 %1, 0

23
test/CodeGen/X86/callbr-asm-branch-folding.ll
View File

@ -24,17 +24,8 @@ define void @n(i32* %o, i32 %p, i32 %u) nounwind {
; CHECK-NEXT: movq %r15, %rdi
; CHECK-NEXT: callq l
; CHECK-NEXT: testl %eax, %eax
; CHECK-NEXT: je .LBB0_1
; CHECK-NEXT: .LBB0_10: # %cleanup
; CHECK-NEXT: addq $8, %rsp
; CHECK-NEXT: popq %rbx
; CHECK-NEXT: popq %r12
; CHECK-NEXT: popq %r13
; CHECK-NEXT: popq %r14
; CHECK-NEXT: popq %r15
; CHECK-NEXT: popq %rbp
; CHECK-NEXT: retq
; CHECK-NEXT: .LBB0_1: # %if.end
; CHECK-NEXT: jne .LBB0_10
; CHECK-NEXT: # %bb.1: # %if.end
; CHECK-NEXT: movl %ebx, {{[-0-9]+}}(%r{{[sb]}}p) # 4-byte Spill
; CHECK-NEXT: cmpl $0, {{.*}}(%rip)
; CHECK-NEXT: # implicit-def: $ebx
@ -82,7 +73,15 @@ define void @n(i32* %o, i32 %p, i32 %u) nounwind {
; CHECK-NEXT: jmp k # TAILCALL
; CHECK-NEXT: .LBB0_9: # %if.else
; CHECK-NEXT: incq 0
; CHECK-NEXT: jmp .LBB0_10
; CHECK-NEXT: .LBB0_10: # %cleanup
; CHECK-NEXT: addq $8, %rsp
; CHECK-NEXT: popq %rbx
; CHECK-NEXT: popq %r12
; CHECK-NEXT: popq %r13
; CHECK-NEXT: popq %r14
; CHECK-NEXT: popq %r15
; CHECK-NEXT: popq %rbp
; CHECK-NEXT: retq
entry:
%call = tail call i32 @c()
%call1 = tail call i32 @l(i32* %o)

17
test/CodeGen/X86/callbr-asm.ll
View File

@ -56,7 +56,7 @@ fail:
; Test 3 - asm-goto implements a loop. The loop gets recognized, but many loop
; transforms fail due to canonicalization having callbr exceptions. Trivial
; blocks at labels 1 and 3 also don't get simplified due to callbr.
define dso_local i32 @test3(i32 %a) {
define i32 @test3(i32 %a) {
; CHECK-LABEL: test3:
; CHECK: # %bb.0: # %entry
; CHECK-NEXT: .Ltmp1: # Block address taken
@ -78,7 +78,6 @@ define dso_local i32 @test3(i32 %a) {
; CHECK-NEXT: # Parent Loop BB2_2 Depth=2
; CHECK-NEXT: # => This Loop Header: Depth=3
; CHECK-NEXT: # Child Loop BB2_4 Depth 4
; CHECK-NEXT: .p2align 4, 0x90
; CHECK-NEXT: .Ltmp4: # Block address taken
; CHECK-NEXT: .LBB2_4: # %label04
; CHECK-NEXT: # Parent Loop BB2_1 Depth=1
@ -134,17 +133,17 @@ normal1: ; preds = %normal0
; Test 4 - asm-goto referenced with the 'l' (ell) modifier and not.
define void @test4() {
; CHECK-LABEL: test4:
; CHECK: # %bb.0:
; CHECK: # %bb.0: # %entry
; CHECK-NEXT: #APP
; CHECK-NOT: ja .Ltmp50
; CHECK-NEXT: ja .Ltmp5
; CHECK-NEXT: ja .Ltmp5{{$}}
; CHECK-NEXT: #NO_APP
; CHECK-NEXT: .LBB3_1:
; CHECK-NEXT: .LBB3_1: # %asm.fallthrough
; CHECK-NEXT: #APP
; CHECK-NOT: ja .Ltmp50
; CHECK-NEXT: ja .Ltmp5
; CHECK-NEXT: ja .Ltmp5{{$}}
; CHECK-NEXT: #NO_APP
; CHECK-NEXT: jmp .LBB3_3
; CHECK-NEXT: .Ltmp5: # Block address taken
; CHECK-NEXT: .LBB3_3: # %quux
; CHECK-NEXT: retl
entry:
callbr void asm sideeffect "ja $0", "X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@test4, %quux))
to label %asm.fallthrough [label %quux]