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[Profile] preserve branch metadata lowering select in CGP

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CGP currently drops select's MD_prof profile data when
generating conditional branch which can lead to bad
code layout. The patch fixes the issue.

Differential Revision: http://reviews.llvm.org/D24169


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280600 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Xinliang David Li 2016-09-03 21:26:36 +00:00
parent 1c224c03d3
commit da48846879
4 changed files with 42 additions and 8 deletions
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13
include/llvm/IR/IRBuilder.h
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@ -703,6 +703,19 @@ public:
BranchWeights, Unpredictable));
}
/// \brief Create a conditional 'br Cond, TrueDest, FalseDest'
/// instruction. Copy branch meta data if available.
BranchInst *CreateCondBr(Value *Cond, BasicBlock *True, BasicBlock *False,
Instruction *MDSrc) {
BranchInst *Br = BranchInst::Create(True, False, Cond);
if (MDSrc) {
unsigned WL[4] = {LLVMContext::MD_prof, LLVMContext::MD_unpredictable,
LLVMContext::MD_make_implicit, LLVMContext::MD_dbg};
Br->copyMetadata(*MDSrc, makeArrayRef(&WL[0], 4));
}
return Insert(Br);
}
/// \brief Create a switch instruction with the specified value, default dest,
/// and with a hint for the number of cases that will be added (for efficient
/// allocation).

11
lib/CodeGen/CodeGenPrepare.cpp
View File

@ -4676,15 +4676,20 @@ bool CodeGenPrepare::optimizeSelectInst(SelectInst *SI) {
// of the condition, it means that side of the branch goes to the end block
// directly and the path originates from the start block from the point of
// view of the new PHI.
BasicBlock *TT, *FT;
if (TrueBlock == nullptr) {
BranchInst::Create(EndBlock, FalseBlock, SI->getCondition(), SI);
TT = EndBlock;
FT = FalseBlock;
TrueBlock = StartBlock;
} else if (FalseBlock == nullptr) {
BranchInst::Create(TrueBlock, EndBlock, SI->getCondition(), SI);
TT = TrueBlock;
FT = EndBlock;
FalseBlock = StartBlock;
} else {
BranchInst::Create(TrueBlock, FalseBlock, SI->getCondition(), SI);
TT = TrueBlock;
FT = FalseBlock;
}
IRBuilder<>(SI).CreateCondBr(SI->getCondition(), TT, FT, SI);
// The select itself is replaced with a PHI Node.
PHINode *PN = PHINode::Create(SI->getType(), 2, "", &EndBlock->front());

10
test/CodeGen/X86/cmov-into-branch.ll
View File

@ -103,11 +103,11 @@ define i32 @weighted_select3(i32 %a, i32 %b) {
; CHECK-LABEL: weighted_select3:
; CHECK: # BB#0:
; CHECK-NEXT: testl %edi, %edi
; CHECK-NEXT: jne [[LABEL_BB6:.*]]
; CHECK: movl %esi, %edi
; CHECK-NEXT: [[LABEL_BB6]]
; CHECK-NEXT: movl %edi, %eax
; CHECK-NEXT: retq
; CHECK-NEXT: je [[LABEL_BB6:.*]]
; CHECK: movl %edi, %eax
; CHECK: [[LABEL_BB6]]
; CHECK-NEXT: movl %esi, %edi
; CHECK-NEXT: jmp
;
%cmp = icmp ne i32 %a, 0
%sel = select i1 %cmp, i32 %a, i32 %b, !prof !2

16
test/CodeGen/X86/select_meta.ll Normal file
View File

@ -0,0 +1,16 @@
; RUN: llc -mtriple=x86_64-unknown-unknown -print-after-all < %s 2>&1 | FileCheck %s
; Function Attrs: norecurse nounwind readnone uwtable
define i32 @foo(i32, i32, i32) {
%4 = and i32 %0, 3
%5 = icmp eq i32 %4, 1
%6 = select i1 %5, i32 %1, i32 %2, !prof !1
; CHECK: br {{.*}}label{{.*}}, label{{.*}}, !prof ![[WT:.*]]
ret i32 %6
}
!llvm.ident = !{!0}
!0 = !{!"clang version 4.0.0 (trunk 279683)"}
!1 = !{!"branch_weights", i32 1000, i32 1 }
; CHECK ![[WT]] = !{!"branch_weights", i32 1000, i32 1 }