From fccf5c6e01a81b0f739e14302bd821a4f86bee94 Mon Sep 17 00:00:00 2001 From: David Majnemer Date: Wed, 27 Jan 2016 02:59:41 +0000 Subject: [PATCH] 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 --- llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 23 +++++++++--- .../SimplifyCFG/X86/speculate-cttz-ctlz.ll | 24 ++++--------- llvm/test/Transforms/SimplifyCFG/speculate-math.ll | 42 +++++++++------------- 3 files changed, 42 insertions(+), 47 deletions(-) diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp index 57adcec..fefe448 100644 --- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp +++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp @@ -85,6 +85,11 @@ static cl::opt 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 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 *AggressiveInsts, unsigned &CostRemaining, - const TargetTransformInfo &TTI) { + const TargetTransformInfo &TTI, + unsigned Depth = 0) { Instruction *I = dyn_cast(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); diff --git a/llvm/test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll b/llvm/test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll index 69f6c69..bee80e6 100644 --- a/llvm/test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll +++ b/llvm/test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll @@ -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 diff --git a/llvm/test/Transforms/SimplifyCFG/speculate-math.ll b/llvm/test/Transforms/SimplifyCFG/speculate-math.ll index 442e867..5655d5d 100644 --- a/llvm/test/Transforms/SimplifyCFG/speculate-math.ll +++ b/llvm/test/Transforms/SimplifyCFG/speculate-math.ll @@ -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 -- 2.7.4