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[Codegen] Decrease minimum jump table density.

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Minimum density for both optsize and non optsize are now options
-sparse-jump-table-density (default 10) for non optsize functions
-dense-jump-table-density (default 40) for optsize functions, which
matches the current default. This improves several benchmarks at google
at the cost of a small codesize increase. For code compiled with -Os,
the old behavior continues

llvm-svn: 264689
This commit is contained in:
Kyle Butt 2016-03-29 00:23:41 +00:00
parent 55e78ca526
commit 7a8a4c3cae
10 changed files with 134 additions and 38 deletions
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26
lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
View File

@ -86,6 +86,19 @@ static cl::opt<bool>
EnableFMFInDAG("enable-fmf-dag", cl::init(true), cl::Hidden,
cl::desc("Enable fast-math-flags for DAG nodes"));
/// Minimum jump table density for normal functions.
static cl::opt<unsigned>
JumpTableDensity("jump-table-density", cl::init(10), cl::Hidden,
cl::desc("Minimum density for building a jump table in "
"a normal function"));
/// Minimum jump table density for -Os or -Oz functions.
static cl::opt<unsigned>
OptsizeJumpTableDensity("optsize-jump-table-density", cl::init(40), cl::Hidden,
cl::desc("Minimum density for building a jump table in "
"an optsize function"));
// Limit the width of DAG chains. This is important in general to prevent
// DAG-based analysis from blowing up. For example, alias analysis and
// load clustering may not complete in reasonable time. It is difficult to
@ -7918,7 +7931,8 @@ void SelectionDAGBuilder::updateDAGForMaybeTailCall(SDValue MaybeTC) {
bool SelectionDAGBuilder::isDense(const CaseClusterVector &Clusters,
unsigned *TotalCases, unsigned First,
unsigned Last) {
unsigned Last,
unsigned Density) {
assert(Last >= First);
assert(TotalCases[Last] >= TotalCases[First]);
@ -7939,7 +7953,7 @@ bool SelectionDAGBuilder::isDense(const CaseClusterVector &Clusters,
assert(NumCases < UINT64_MAX / 100);
assert(Range >= NumCases);
return NumCases * 100 >= Range * MinJumpTableDensity;
return NumCases * 100 >= Range * Density;
}
static inline bool areJTsAllowed(const TargetLowering &TLI) {
@ -8053,7 +8067,11 @@ void SelectionDAGBuilder::findJumpTables(CaseClusterVector &Clusters,
TotalCases[i] += TotalCases[i - 1];
}
if (N >= MinJumpTableSize && isDense(Clusters, &TotalCases[0], 0, N - 1)) {
unsigned MinDensity = JumpTableDensity;
if (DefaultMBB->getParent()->getFunction()->optForSize())
MinDensity = OptsizeJumpTableDensity;
if (N >= MinJumpTableSize
&& isDense(Clusters, &TotalCases[0], 0, N - 1, MinDensity)) {
// Cheap case: the whole range might be suitable for jump table.
CaseCluster JTCluster;
if (buildJumpTable(Clusters, 0, N - 1, SI, DefaultMBB, JTCluster)) {
@ -8098,7 +8116,7 @@ void SelectionDAGBuilder::findJumpTables(CaseClusterVector &Clusters,
// Search for a solution that results in fewer partitions.
for (int64_t j = N - 1; j > i; j--) {
// Try building a partition from Clusters[i..j].
if (isDense(Clusters, &TotalCases[0], i, j)) {
if (isDense(Clusters, &TotalCases[0], i, j, MinDensity)) {
unsigned NumPartitions = 1 + (j == N - 1 ? 0 : MinPartitions[j + 1]);
bool IsTable = j - i + 1 >= MinJumpTableSize;
unsigned Tables = IsTable + (j == N - 1 ? 0 : NumTables[j + 1]);

5
lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
View File

@ -303,12 +303,9 @@ private:
BranchProbability DefaultProb;
};
/// Minimum jump table density, in percent.
enum { MinJumpTableDensity = 40 };
/// Check whether a range of clusters is dense enough for a jump table.
bool isDense(const CaseClusterVector &Clusters, unsigned *TotalCases,
unsigned First, unsigned Last);
unsigned First, unsigned Last, unsigned MinDensity);
/// Build a jump table cluster from Clusters[First..Last]. Returns false if it
/// decides it's not a good idea.

2
test/CodeGen/ARM/2011-08-25-ldmia_ret.ll
View File

@ -1,4 +1,4 @@
; RUN: llc < %s -mtriple=thumbv7-apple-ios -mcpu=cortex-a9 | FileCheck %s
; RUN: llc < %s -mtriple=thumbv7-apple-ios -mcpu=cortex-a9 -jump-table-density=40 | FileCheck %s
; Test that ldmia_ret preserves implicit operands for return values.
;
; This CFG is reduced from a benchmark miscompile. With current

14
test/CodeGen/Generic/MachineBranchProb.ll
View File

@ -41,11 +41,11 @@ define void @left_leaning_weight_balanced_tree(i32 %x) {
entry:
switch i32 %x, label %return [
i32 0, label %bb0
i32 10, label %bb1
i32 20, label %bb2
i32 30, label %bb3
i32 40, label %bb4
i32 50, label %bb5
i32 100, label %bb1
i32 200, label %bb2
i32 300, label %bb3
i32 400, label %bb4
i32 500, label %bb5
], !prof !1
bb0: tail call void @g(i32 0) br label %return
bb1: tail call void @g(i32 1) br label %return
@ -68,7 +68,7 @@ return: ret void
!1 = !{!"branch_weights",
; Default:
i32 1,
; Case 0, 10, 20:
; Case 0, 100, 200:
i32 10, i32 1, i32 1,
; Case 30, 40, 50:
; Case 300, 400, 500:
i32 1, i32 10, i32 10}

6
test/CodeGen/PowerPC/pr26690.ll
View File

@ -35,9 +35,9 @@ while.body.lr.ph: ; preds = %while.cond.preheade
while.body: ; preds = %while.body.backedge, %while.body.lr.ph
switch i32 %.pre, label %while.body.backedge [
i32 0, label %sw.bb1
i32 8, label %sw.bb1
i32 6, label %sw.bb1
i32 24, label %while.cond.backedge
i32 80, label %sw.bb1
i32 60, label %sw.bb1
i32 240, label %while.cond.backedge
]
while.body.backedge: ; preds = %while.body, %while.cond.backedge

20
test/CodeGen/Thumb2/ldr-str-imm12.ll
View File

@ -29,16 +29,16 @@ entry:
bb20: ; preds = %entry
switch i32 undef, label %bb1287 [
i32 11, label %bb119
i32 12, label %bb119
i32 21, label %bb420
i32 23, label %bb420
i32 45, label %bb438
i32 46, label %bb438
i32 55, label %bb533
i32 56, label %bb569
i32 64, label %bb745
i32 78, label %bb1098
i32 110, label %bb119
i32 120, label %bb119
i32 210, label %bb420
i32 230, label %bb420
i32 450, label %bb438
i32 460, label %bb438
i32 550, label %bb533
i32 560, label %bb569
i32 640, label %bb745
i32 780, label %bb1098
]
bb119: ; preds = %bb20, %bb20

2
test/CodeGen/X86/switch-bt.ll
View File

@ -1,4 +1,4 @@
; RUN: llc -march=x86-64 -asm-verbose=false < %s | FileCheck %s
; RUN: llc -march=x86-64 -asm-verbose=false < %s -jump-table-density=40 | FileCheck %s
; This switch should use bit tests, and the third bit test case is just
; testing for one possible value, so it doesn't need a bt.

81
test/CodeGen/X86/switch-density.ll Normal file
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@ -0,0 +1,81 @@
; RUN: llc -mtriple=x86_64-linux-gnu %s -o - -jump-table-density=25 | FileCheck %s --check-prefix=DENSE --check-prefix=CHECK
; RUN: llc -mtriple=x86_64-linux-gnu %s -o - -jump-table-density=10 | FileCheck %s --check-prefix=SPARSE --check-prefix=CHECK
declare void @g(i32)
define void @sparse(i32 %x) {
entry:
switch i32 %x, label %return [
i32 300, label %bb0
i32 100, label %bb1
i32 400, label %bb1
i32 500, label %bb2
]
bb0: tail call void @g(i32 0) br label %return
bb1: tail call void @g(i32 1) br label %return
bb2: tail call void @g(i32 1) br label %return
return: ret void
; Should pivot around 400 for two subtrees with two jump tables each.
; CHECK-LABEL: sparse
; CHECK-NOT: cmpl
; CHECK: cmpl $399
; CHECK: cmpl $100
; CHECK: cmpl $300
; CHECK: cmpl $400
; CHECK: cmpl $500
}
define void @med(i32 %x) {
entry:
switch i32 %x, label %return [
i32 30, label %bb0
i32 10, label %bb1
i32 40, label %bb1
i32 50, label %bb2
i32 20, label %bb3
]
bb0: tail call void @g(i32 0) br label %return
bb1: tail call void @g(i32 1) br label %return
bb2: tail call void @g(i32 1) br label %return
bb3: tail call void @g(i32 2) br label %return
return: ret void
; Lowered as a jump table when sparse, and branches when dense.
; CHECK-LABEL: med
; SPARSE: addl $-10
; SPARSE: cmpl $40
; SPARSE: ja
; SPARSE: jmpq *.LJTI
; DENSE-NOT: cmpl
; DENSE: cmpl $29
; DENSE-DAG: cmpl $10
; DENSE-DAG: cmpl $20
; DENSE-DAG: cmpl $30
; DENSE-DAG: cmpl $40
; DENSE-DAG: cmpl $50
; DENSE: retq
}
define void @dense(i32 %x) {
entry:
switch i32 %x, label %return [
i32 12, label %bb0
i32 4, label %bb1
i32 16, label %bb1
i32 20, label %bb2
i32 8, label %bb3
]
bb0: tail call void @g(i32 0) br label %return
bb1: tail call void @g(i32 1) br label %return
bb2: tail call void @g(i32 1) br label %return
bb3: tail call void @g(i32 2) br label %return
return: ret void
; Lowered as a jump table when sparse, and branches when dense.
; CHECK-LABEL: dense
; CHECK: addl $-4
; CHECK: cmpl $16
; CHECK: ja
; CHECK: jmpq *.LJTI
}

12
test/CodeGen/X86/switch-edge-weight.ll
View File

@ -233,11 +233,11 @@ entry:
; block.
switch i32 %x, label %sw.default [
i32 1, label %sw.bb
i32 5, label %sw.bb2
i32 7, label %sw.bb3
i32 9, label %sw.bb4
i32 31, label %sw.bb5
i32 4, label %sw.bb
i32 20, label %sw.bb2
i32 28, label %sw.bb3
i32 36, label %sw.bb4
i32 124, label %sw.bb5
], !prof !2
sw.bb:
@ -272,7 +272,7 @@ sw.epilog:
;
; CHECK: BB#0:
; BB#0 to BB#6: [10, UINT32_MAX] (15)
; BB#0 to BB#8: [1, 5, 7, 9] (jump table) (45)
; BB#0 to BB#8: [4, 20, 28, 36] (jump table) (45)
; CHECK: Successors according to CFG: BB#8({{[0-9a-fx/= ]+}}25.00%) BB#9({{[0-9a-fx/= ]+}}75.00%)
}

4
test/CodeGen/X86/switch.ll
View File

@ -1,5 +1,5 @@
; RUN: llc -mtriple=x86_64-linux-gnu %s -o - | FileCheck %s
; RUN: llc -mtriple=x86_64-linux-gnu %s -o - -O0 | FileCheck --check-prefix=NOOPT %s
; RUN: llc -mtriple=x86_64-linux-gnu %s -o - -jump-table-density=40 | FileCheck %s
; RUN: llc -mtriple=x86_64-linux-gnu %s -o - -O0 -jump-table-density=40 | FileCheck --check-prefix=NOOPT %s
declare void @g(i32)