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use "unpredictable" metadata in SelectionDAG when splitting compares

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This patch uses the metadata defined in D12341 to avoid creating an unpredictable branch.

Differential Revision: http://reviews.llvm.org/D12343

llvm-svn: 246691
This commit is contained in:
Sanjay Patel 2015-09-02 19:17:25 +00:00
parent 9c0479fa99
commit 3f57358b22
2 changed files with 33 additions and 6 deletions
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9
lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
View File

@ -1625,11 +1625,12 @@ void SelectionDAGBuilder::visitBr(const BranchInst &I) {
// jle foo
//
if (const BinaryOperator *BOp = dyn_cast<BinaryOperator>(CondVal)) {
if (!DAG.getTargetLoweringInfo().isJumpExpensive() &&
BOp->hasOneUse() && (BOp->getOpcode() == Instruction::And ||
BOp->getOpcode() == Instruction::Or)) {
Instruction::BinaryOps Opcode = BOp->getOpcode();
if (!DAG.getTargetLoweringInfo().isJumpExpensive() && BOp->hasOneUse() &&
!I.getMetadata(LLVMContext::MD_unpredictable) &&
(Opcode == Instruction::And || Opcode == Instruction::Or)) {
FindMergedConditions(BOp, Succ0MBB, Succ1MBB, BrMBB, BrMBB,
BOp->getOpcode(), getEdgeWeight(BrMBB, Succ0MBB),
Opcode, getEdgeWeight(BrMBB, Succ0MBB),
getEdgeWeight(BrMBB, Succ1MBB));
// If the compares in later blocks need to use values not currently
// exported from this block, export them now. This block should always

30
test/CodeGen/X86/or-branch.ll
View File

@ -1,5 +1,5 @@
; RUN: llc < %s -mtriple=i386-unknown-unknown -jump-is-expensive=0 | FileCheck %s --check-prefix=JUMP2
; RUN: llc < %s -mtriple=i386-unknown-unknown -jump-is-expensive=1 | FileCheck %s --check-prefix=JUMP1
; RUN: llc < %s -mtriple=i386-unknown-unknown -jump-is-expensive=0 | FileCheck %s --check-prefix=JUMP2 --check-prefix=CHECK
; RUN: llc < %s -mtriple=i386-unknown-unknown -jump-is-expensive=1 | FileCheck %s --check-prefix=JUMP1 --check-prefix=CHECK
define void @foo(i32 %X, i32 %Y, i32 %Z) nounwind {
; JUMP2-LABEL: foo:
@ -25,4 +25,30 @@ UnifiedReturnBlock:
ret void
}
; If the branch is unpredictable, don't add another branch
; regardless of whether they are expensive or not.
define void @unpredictable(i32 %X, i32 %Y, i32 %Z) nounwind {
; CHECK-LABEL: unpredictable:
; CHECK-DAG: sete
; CHECK-DAG: setl
; CHECK: orb
; CHECK: jne
entry:
%tmp1 = icmp eq i32 %X, 0
%tmp3 = icmp slt i32 %Y, 5
%tmp4 = or i1 %tmp3, %tmp1
br i1 %tmp4, label %cond_true, label %UnifiedReturnBlock, !unpredictable !0
cond_true:
%tmp5 = tail call i32 (...) @bar( )
ret void
UnifiedReturnBlock:
ret void
}
declare i32 @bar(...)
!0 = !{}