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Revert "Revert "[SimplifyCFG] allow speculation of exactly one expensive instruction (PR24818)"" 

This reverts commit r258903 which reverted r255660.  r258903 was an
accidental commit and should not have been committed.

llvm-svn: 258905
This commit is contained in:
David Majnemer 2016-01-27 02:59:41 +00:00
parent c761afd1d1
commit fccf5c6e01
3 changed files with 42 additions and 47 deletions
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23
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -85,6 +85,11 @@ static cl::opt<bool> MergeCondStoresAggressively(
cl::desc("When merging conditional stores, do so even if the resultant "
"basic blocks are unlikely to be if-converted as a result"));
static cl::opt<bool> SpeculateOneExpensiveInst(
"speculate-one-expensive-inst", cl::Hidden, cl::init(true),
cl::desc("Allow exactly one expensive instruction to be speculatively "
"executed"));
STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps");
STATISTIC(NumLinearMaps, "Number of switch instructions turned into linear mapping");
STATISTIC(NumLookupTables, "Number of switch instructions turned into lookup tables");
@ -262,7 +267,8 @@ static unsigned ComputeSpeculationCost(const User *I,
static bool DominatesMergePoint(Value *V, BasicBlock *BB,
SmallPtrSetImpl<Instruction*> *AggressiveInsts,
unsigned &CostRemaining,
const TargetTransformInfo &TTI) {
const TargetTransformInfo &TTI,
unsigned Depth = 0) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I) {
// Non-instructions all dominate instructions, but not all constantexprs
@ -300,15 +306,24 @@ static bool DominatesMergePoint(Value *V, BasicBlock *BB,
unsigned Cost = ComputeSpeculationCost(I, TTI);
if (Cost > CostRemaining)
// Allow exactly one instruction to be speculated regardless of its cost
// (as long as it is safe to do so).
// This is intended to flatten the CFG even if the instruction is a division
// or other expensive operation. The speculation of an expensive instruction
// is expected to be undone in CodeGenPrepare if the speculation has not
// enabled further IR optimizations.
if (Cost > CostRemaining &&
(!SpeculateOneExpensiveInst || !AggressiveInsts->empty() || Depth > 0))
return false;
CostRemaining -= Cost;
// Avoid unsigned wrap.
CostRemaining = (Cost > CostRemaining) ? 0 : CostRemaining - Cost;
// Okay, we can only really hoist these out if their operands do
// not take us over the cost threshold.
for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining, TTI))
if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining, TTI,
Depth + 1))
return false;
// Okay, it's safe to do this! Remember this instruction.
AggressiveInsts->insert(I);

24
llvm/test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll
View File

@ -7,9 +7,7 @@ define i64 @test1(i64 %A) {
; ALL-LABEL: @test1(
; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i64 %A, 0
; ALL: [[CTLZ:%[A-Za-z0-9]+]] = tail call i64 @llvm.ctlz.i64(i64 %A, i1 true)
; LZCNT-NEXT: select i1 [[COND]], i64 64, i64 [[CTLZ]]
; BMI-NOT: select
; GENERIC-NOT: select
; ALL-NEXT: select i1 [[COND]], i64 64, i64 [[CTLZ]]
; ALL: ret
entry:
%tobool = icmp eq i64 %A, 0
@ -28,9 +26,7 @@ define i32 @test2(i32 %A) {
; ALL-LABEL: @test2(
; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i32 %A, 0
; ALL: [[CTLZ:%[A-Za-z0-9]+]] = tail call i32 @llvm.ctlz.i32(i32 %A, i1 true)
; LZCNT-NEXT: select i1 [[COND]], i32 32, i32 [[CTLZ]]
; BMI-NOT: select
; GENERIC-NOT: select
; ALL-NEXT: select i1 [[COND]], i32 32, i32 [[CTLZ]]
; ALL: ret
entry:
%tobool = icmp eq i32 %A, 0
@ -50,9 +46,7 @@ define signext i16 @test3(i16 signext %A) {
; ALL-LABEL: @test3(
; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i16 %A, 0
; ALL: [[CTLZ:%[A-Za-z0-9]+]] = tail call i16 @llvm.ctlz.i16(i16 %A, i1 true)
; LZCNT-NEXT: select i1 [[COND]], i16 16, i16 [[CTLZ]]
; BMI-NOT: select
; GENERIC-NOT: select
; ALL-NEXT: select i1 [[COND]], i16 16, i16 [[CTLZ]]
; ALL: ret
entry:
%tobool = icmp eq i16 %A, 0
@ -72,9 +66,7 @@ define i64 @test1b(i64 %A) {
; ALL-LABEL: @test1b(
; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i64 %A, 0
; ALL: [[CTTZ:%[A-Za-z0-9]+]] = tail call i64 @llvm.cttz.i64(i64 %A, i1 true)
; BMI-NEXT: select i1 [[COND]], i64 64, i64 [[CTTZ]]
; LZCNT-NOT: select
; GENERIC-NOT: select
; ALL-NEXT: select i1 [[COND]], i64 64, i64 [[CTTZ]]
; ALL: ret
entry:
%tobool = icmp eq i64 %A, 0
@ -94,9 +86,7 @@ define i32 @test2b(i32 %A) {
; ALL-LABEL: @test2b(
; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i32 %A, 0
; ALL: [[CTTZ:%[A-Za-z0-9]+]] = tail call i32 @llvm.cttz.i32(i32 %A, i1 true)
; BMI-NEXT: select i1 [[COND]], i32 32, i32 [[CTTZ]]
; LZCNT-NOT: select
; GENERIC-NOT: select
; ALL-NEXT: select i1 [[COND]], i32 32, i32 [[CTTZ]]
; ALL: ret
entry:
%tobool = icmp eq i32 %A, 0
@ -116,9 +106,7 @@ define signext i16 @test3b(i16 signext %A) {
; ALL-LABEL: @test3b(
; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i16 %A, 0
; ALL: [[CTTZ:%[A-Za-z0-9]+]] = tail call i16 @llvm.cttz.i16(i16 %A, i1 true)
; BMI-NEXT: select i1 [[COND]], i16 16, i16 [[CTTZ]]
; LZCNT-NOT: select
; GENERIC-NOT: select
; ALL-NEXT: select i1 [[COND]], i16 16, i16 [[CTTZ]]
; ALL: ret
entry:
%tobool = icmp eq i16 %A, 0

42
llvm/test/Transforms/SimplifyCFG/speculate-math.ll
View File

@ -1,4 +1,5 @@
; RUN: opt -S -simplifycfg -phi-node-folding-threshold=2 < %s | FileCheck %s
; RUN: opt -S -simplifycfg < %s | FileCheck %s --check-prefix=EXPENSIVE --check-prefix=ALL
; RUN: opt -S -simplifycfg -speculate-one-expensive-inst=false < %s | FileCheck %s --check-prefix=CHEAP --check-prefix=ALL
declare float @llvm.sqrt.f32(float) nounwind readonly
declare float @llvm.fma.f32(float, float, float) nounwind readonly
@ -7,19 +8,10 @@ declare float @llvm.fabs.f32(float) nounwind readonly
declare float @llvm.minnum.f32(float, float) nounwind readonly
declare float @llvm.maxnum.f32(float, float) nounwind readonly
; FIXME: This is intended to be a temporary test. As discussed in
; D12882, we actually do want to speculate even expensive operations
; in SimplifyCFG because it can expose more optimizations for other
; passes. Therefore, we either need to adjust SimplifyCFG's
; calculations that use the TTI cost model or use a different cost
; model for deciding which ops should be speculated in SimplifyCFG.
; We should also be using the TTI cost model later - for example in
; CodeGenPrepare - to potentially undo this speculation.
; ALL-LABEL: @fdiv_test(
; EXPENSIVE: select i1 %cmp, double %div, double 0.0
; CHEAP-NOT: select
; Do not speculate fdiv by default because it is generally expensive.
; CHECK-LABEL: @fdiv_test(
; CHECK-NOT: select
define double @fdiv_test(double %a, double %b) {
entry:
%cmp = fcmp ogt double %a, 0.0
@ -34,8 +26,8 @@ cond.end:
ret double %cond
}
; CHECK-LABEL: @sqrt_test(
; CHECK: select
; ALL-LABEL: @sqrt_test(
; ALL: select
define void @sqrt_test(float addrspace(1)* noalias nocapture %out, float %a) nounwind {
entry:
%cmp.i = fcmp olt float %a, 0.000000e+00
@ -51,8 +43,8 @@ test_sqrt.exit: ; preds = %cond.else.i, %entry
ret void
}
; CHECK-LABEL: @fabs_test(
; CHECK: select
; ALL-LABEL: @fabs_test(
; ALL: select
define void @fabs_test(float addrspace(1)* noalias nocapture %out, float %a) nounwind {
entry:
%cmp.i = fcmp olt float %a, 0.000000e+00
@ -68,8 +60,8 @@ test_fabs.exit: ; preds = %cond.else.i, %entry
ret void
}
; CHECK-LABEL: @fma_test(
; CHECK: select
; ALL-LABEL: @fma_test(
; ALL: select
define void @fma_test(float addrspace(1)* noalias nocapture %out, float %a, float %b, float %c) nounwind {
entry:
%cmp.i = fcmp olt float %a, 0.000000e+00
@ -85,8 +77,8 @@ test_fma.exit: ; preds = %cond.else.i, %entry
ret void
}
; CHECK-LABEL: @fmuladd_test(
; CHECK: select
; ALL-LABEL: @fmuladd_test(
; ALL: select
define void @fmuladd_test(float addrspace(1)* noalias nocapture %out, float %a, float %b, float %c) nounwind {
entry:
%cmp.i = fcmp olt float %a, 0.000000e+00
@ -102,8 +94,8 @@ test_fmuladd.exit: ; preds = %cond.else.i, %en
ret void
}
; CHECK-LABEL: @minnum_test(
; CHECK: select
; ALL-LABEL: @minnum_test(
; ALL: select
define void @minnum_test(float addrspace(1)* noalias nocapture %out, float %a, float %b) nounwind {
entry:
%cmp.i = fcmp olt float %a, 0.000000e+00
@ -119,8 +111,8 @@ test_minnum.exit: ; preds = %cond.else.i, %ent
ret void
}
; CHECK-LABEL: @maxnum_test(
; CHECK: select
; ALL-LABEL: @maxnum_test(
; ALL: select
define void @maxnum_test(float addrspace(1)* noalias nocapture %out, float %a, float %b) nounwind {
entry:
%cmp.i = fcmp olt float %a, 0.000000e+00