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[ConstHoisting] choose to hoist when frequency is the same.

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The patch is to adjust the strategy of frequency based consthoisting:
Previously when the candidate block has the same frequency with the existing
blocks containing a const, it will not hoist the const to the candidate block.
For that case, now we change the strategy to hoist the const if only existing
blocks have more than one block member. This is helpful for reducing code size.

Differential Revision: https://reviews.llvm.org/D35084

llvm-svn: 307328
This commit is contained in:
Wei Mi 2017-07-06 22:32:27 +00:00
parent dc71dcb613
commit 538215e467
3 changed files with 63 additions and 6 deletions
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4
include/llvm/Support/BlockFrequency.h
View File

@ -71,6 +71,10 @@ public:
bool operator>=(BlockFrequency RHS) const {
return Frequency >= RHS.Frequency;
}
bool operator==(BlockFrequency RHS) const {
return Frequency == RHS.Frequency;
}
};
}

13
lib/Transforms/Scalar/ConstantHoisting.cpp
View File

@ -231,7 +231,8 @@ static void findBestInsertionSet(DominatorTree &DT, BlockFrequencyInfo &BFI,
// Return the optimal insert points in BBs.
if (Node == Entry) {
BBs.clear();
if (InsertPtsFreq > BFI.getBlockFreq(Node))
if (InsertPtsFreq > BFI.getBlockFreq(Node) ||
(InsertPtsFreq == BFI.getBlockFreq(Node) && InsertPts.size() > 1))
BBs.insert(Entry);
else
BBs.insert(InsertPts.begin(), InsertPts.end());
@ -244,7 +245,15 @@ static void findBestInsertionSet(DominatorTree &DT, BlockFrequencyInfo &BFI,
SmallPtrSet<BasicBlock *, 16> &ParentInsertPts = InsertPtsMap[Parent].first;
BlockFrequency &ParentPtsFreq = InsertPtsMap[Parent].second;
// Choose to insert in Node or in subtree of Node.
if (InsertPtsFreq > BFI.getBlockFreq(Node) || NodeInBBs) {
// Don't hoist to EHPad because we may not find a proper place to insert
// in EHPad.
// If the total frequency of InsertPts is the same as the frequency of the
// target Node, and InsertPts contains more than one nodes, choose hoisting
// to reduce code size.
if (NodeInBBs ||
(!Node->isEHPad() &&
(InsertPtsFreq > BFI.getBlockFreq(Node) ||
(InsertPtsFreq == BFI.getBlockFreq(Node) && InsertPts.size() > 1)))) {
ParentInsertPts.insert(Node);
ParentPtsFreq += BFI.getBlockFreq(Node);
} else {

52
test/CodeGen/X86/constant-hoisting-bfi.ll
View File

@ -4,13 +4,13 @@ target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
; Check when BFI is enabled for constant hoisting, constant 214748364701
; will not be hoisted to the func entry.
; CHECK-LABEL: @foo(
; CHECK-LABEL: @test1(
; CHECK: entry:
; CHECK-NOT: bitcast i64 214748364701 to i64
; CHECK: if.then:
; Function Attrs: norecurse nounwind uwtable
define i64 @foo(i64* nocapture %a) {
define i64 @test1(i64* nocapture %a) {
entry:
%arrayidx = getelementptr inbounds i64, i64* %a, i64 9
%t0 = load i64, i64* %arrayidx, align 8
@ -52,7 +52,7 @@ return: ; preds = %if.else5, %if.then,
; in while.body will be hoisted to while.body.preheader. 214748364701 in
; if.then16 and if.else10 will be merged and hoisted to the beginning of
; if.else10 because if.else10 dominates if.then16.
; CHECK-LABEL: @goo(
; CHECK-LABEL: @test2(
; CHECK: entry:
; CHECK-NOT: bitcast i64 214748364701 to i64
; CHECK: while.body.preheader:
@ -61,7 +61,7 @@ return: ; preds = %if.else5, %if.then,
; CHECK: if.else10:
; CHECK-NEXT: bitcast i64 214748364701 to i64
; CHECK-NOT: bitcast i64 214748364701 to i64
define i64 @goo(i64* nocapture %a) {
define i64 @test2(i64* nocapture %a) {
entry:
%arrayidx = getelementptr inbounds i64, i64* %a, i64 9
%t0 = load i64, i64* %arrayidx, align 8
@ -113,3 +113,47 @@ return: ; preds = %while.cond.preheade
}
!0 = !{!"branch_weights", i32 1, i32 2000}
; 214748364701 will be hoisted to entry block to reduce code size.
; CHECK-LABEL: @test3(
; CHECK: entry:
; CHECK-NEXT: %const = bitcast i64 214748364701 to i64
define i64 @test3(i64 %t0) {
entry:
%cmp = icmp ult i64 %t0, 56
br i1 %cmp, label %if.then, label %if.else
; CHECK: if.then:
; CHECK-NOT: %const = bitcast i64 214748364701 to i64
if.then:
%add1 = add i64 %t0, 214748364701
br label %return
; CHECK: if.else:
; CHECK-NOT: %const = bitcast i64 214748364701 to i64
if.else:
%add2 = add i64 %t0, 214748364701
br label %return
return:
%retval = phi i64 [ %add1, %if.then ], [ %add2, %if.else ]
ret i64 %retval
}
; 214748364701 will not be hoisted to entry block because it will only
; increase its live range.
; CHECK-LABEL: @test4(
; CHECK: nextblock:
; CHECK-NEXT: %add1 = add i64 %t0, 214748364701
define i64 @test4(i64 %t0) {
entry:
%cmp = icmp ult i64 %t0, 56
br label %nextblock
nextblock:
%add1 = add i64 %t0, 214748364701
br label %return
return:
ret i64 %add1
}