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use "unpredictable" metadata in fast-isel when splitting compares 

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

Differential Revision: http://reviews.llvm.org/D12342

llvm-svn: 246692
This commit is contained in:
Sanjay Patel 2015-09-02 19:23:23 +00:00
parent fff7c6dc73
commit 42574203e5
2 changed files with 56 additions and 1 deletions
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5
llvm/lib/CodeGen/CodeGenPrepare.cpp
View File

@ -4667,6 +4667,10 @@ bool CodeGenPrepare::splitBranchCondition(Function &F) {
if (!match(BB.getTerminator(), m_Br(m_OneUse(m_BinOp(LogicOp)), TBB, FBB)))
continue;
auto *Br1 = cast<BranchInst>(BB.getTerminator());
if (Br1->getMetadata(LLVMContext::MD_unpredictable))
continue;
unsigned Opc;
Value *Cond1, *Cond2;
if (match(LogicOp, m_And(m_OneUse(m_Value(Cond1)),
@ -4693,7 +4697,6 @@ bool CodeGenPrepare::splitBranchCondition(Function &F) {
// Update original basic block by using the first condition directly by the
// branch instruction and removing the no longer needed and/or instruction.
auto *Br1 = cast<BranchInst>(BB.getTerminator());
Br1->setCondition(Cond1);
LogicOp->eraseFromParent();

52
llvm/test/CodeGen/AArch64/fast-isel-branch-cond-split.ll
View File

@ -36,7 +36,59 @@ bb4:
ret i64 %2
}
; If the branch is unpredictable, don't add another branch.
; CHECK-LABEL: test_or_unpredictable
; CHECK: cmp w0, #0
; CHECK-NEXT: cset w8, eq
; CHECK-NEXT: cmp w1, #0
; CHECK-NEXT: cset w9, eq
; CHECK-NEXT: orr w8, w8, w9
; CHECK-NEXT: and w8, w8, #0x1
; CHECK-NEXT: cmp w8, #0
; CHECK-NEXT: b.ne
define i64 @test_or_unpredictable(i32 %a, i32 %b) {
bb1:
%0 = icmp eq i32 %a, 0
%1 = icmp eq i32 %b, 0
%or.cond = or i1 %0, %1
br i1 %or.cond, label %bb3, label %bb4, !unpredictable !2
bb3:
ret i64 0
bb4:
%2 = call i64 @bar()
ret i64 %2
}
; CHECK-LABEL: test_and_unpredictable
; CHECK: cmp w0, #0
; CHECK-NEXT: cset w8, ne
; CHECK-NEXT: cmp w1, #0
; CHECK-NEXT: cset w9, ne
; CHECK-NEXT: and w8, w8, w9
; CHECK-NEXT: and w8, w8, #0x1
; CHECK-NEXT: cmp w8, #0
; CHECK-NEXT: b.eq
define i64 @test_and_unpredictable(i32 %a, i32 %b) {
bb1:
%0 = icmp ne i32 %a, 0
%1 = icmp ne i32 %b, 0
%or.cond = and i1 %0, %1
br i1 %or.cond, label %bb4, label %bb3, !unpredictable !2
bb3:
ret i64 0
bb4:
%2 = call i64 @bar()
ret i64 %2
}
declare i64 @bar()
!0 = !{!"branch_weights", i32 5128, i32 32}
!1 = !{!"branch_weights", i32 1024, i32 4136}
!2 = !{}