[llvm] r258905 - Revert "Revert "[SimplifyCFG] allow speculation of exactly one expensive instruction (PR24818)""
David Majnemer via llvm-commits
llvm-commits at lists.llvm.org
Tue Jan 26 18:59:42 PST 2016
Author: majnemer
Date: Tue Jan 26 20:59:41 2016
New Revision: 258905
URL: http://llvm.org/viewvc/llvm-project?rev=258905&view=rev
Log:
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.
Modified:
llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
llvm/trunk/test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll
llvm/trunk/test/Transforms/SimplifyCFG/speculate-math.ll
Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=258905&r1=258904&r2=258905&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Tue Jan 26 20:59:41 2016
@@ -85,6 +85,11 @@ static cl::opt<bool> MergeCondStoresAggr
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(c
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
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);
Modified: llvm/trunk/test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll?rev=258905&r1=258904&r2=258905&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll Tue Jan 26 20:59:41 2016
@@ -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 %
; 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
Modified: llvm/trunk/test/Transforms/SimplifyCFG/speculate-math.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/speculate-math.ll?rev=258905&r1=258904&r2=258905&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/speculate-math.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyCFG/speculate-math.ll Tue Jan 26 20:59:41 2016
@@ -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) noun
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:
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:
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:
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:
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:
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
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