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[SCEV] Make MulOpsInlineThreshold lower to avoid excessive compilation time 

MulOpsInlineThreshold option of SCEV is defaulted to 1000, which is inadequately high.
When constructing SCEVs of expressions like:

  x1 = a * a
  x2 = x1 * x1
  x3 = x2 * x2
    ...

We actually have huge SCEVs with max allowed amount of operands inlined.
Such expressions are easy to get from unrolling of loops looking like

  x = a
  for (i = 0; i < n; i++)
    x = x * x

Or more tricky cases where big powers are involved. If some non-linear analysis
tries to work with a SCEV that has 1000 operands, it may lead to excessively long
compilation. The attached test does not pass within 1 minute with default threshold.

This patch decreases its default value to 32, which looks much more reasonable if we
use analyzes with complexity O(N^2) or O(N^3) working with SCEV.

Differential Revision: https://reviews.llvm.org/D34397

llvm-svn: 305882
This commit is contained in:
Max Kazantsev 2017-06-21 07:28:13 +00:00
parent 2c8e3ed00f
commit eac01d4c62
2 changed files with 88 additions and 1 deletions
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2
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -126,7 +126,7 @@ static cl::opt<bool>
static cl::opt<unsigned> MulOpsInlineThreshold(
"scev-mulops-inline-threshold", cl::Hidden,
cl::desc("Threshold for inlining multiplication operands into a SCEV"),
cl::init(1000));
cl::init(32));
static cl::opt<unsigned> AddOpsInlineThreshold(
"scev-addops-inline-threshold", cl::Hidden,

87
llvm/test/Transforms/IndVarSimplify/huge_muls.ll Normal file
View File

@ -0,0 +1,87 @@
; RUN: opt < %s -indvars -S | FileCheck %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
; This test takes excessively long time if SCEV tries to construct huge
; SCEVMulExpr's (with ~1000 ops) due to non-linear analysis cost.
define i32 @test() {
; CHECK-LABEL: @test(
bci_0:
br label %bci_12
bci_133: ; preds = %bci_127.unr-lcssa
ret i32 %tmp17
bci_12: ; preds = %bci_127.unr-lcssa, %bci_0
%indvars.iv184 = phi i64 [ %indvars.iv.next185, %bci_127.unr-lcssa ], [ 3, %bci_0 ]
%tmp1 = trunc i64 %indvars.iv184 to i32
br label %bci_55.postloop
bci_127.unr-lcssa: ; preds = %bci_90.postloop
%indvars.iv.next185 = add nuw nsw i64 %indvars.iv184, 1
%tmp4 = icmp sgt i64 %indvars.iv184, 91
br i1 %tmp4, label %bci_133, label %bci_12
bci_55.postloop: ; preds = %bci_90.postloop, %bci_12
%indvars.iv180.postloop = phi i64 [ %indvars.iv.next181.postloop, %bci_90.postloop ], [ 15, %bci_12 ]
%local_2_16.postloop = phi i32 [ %tmp17, %bci_90.postloop ], [ 4, %bci_12 ]
%indvars.iv.next181.postloop = add nuw nsw i64 %indvars.iv180.postloop, 1
%tmp6 = load i32, i32 addrspace(1)* undef, align 4
%tmp7 = mul i32 %tmp6, %tmp1
br label %not_zero65.us.postloop
not_zero65.us.postloop: ; preds = %not_zero65.us.postloop.1, %bci_55.postloop
%local_2_24.us.postloop = phi i32 [ %local_2_16.postloop, %bci_55.postloop ], [ %tmp49, %not_zero65.us.postloop.1 ]
%local_6_.us.postloop = phi i32 [ 3, %bci_55.postloop ], [ %tmp50, %not_zero65.us.postloop.1 ]
%tmp8 = mul i32 %tmp7, %local_2_24.us.postloop
%tmp9 = mul i32 %tmp8, %local_2_24.us.postloop
%tmp10 = mul i32 %tmp7, %tmp9
%tmp11 = mul i32 %tmp10, %tmp9
%tmp12 = mul i32 %tmp7, %tmp11
%tmp13 = mul i32 %tmp12, %tmp11
%tmp14 = mul i32 %tmp7, %tmp13
%tmp15 = mul i32 %tmp14, %tmp13
%tmp16 = mul i32 %tmp7, %tmp15
%tmp17 = mul i32 %tmp16, %tmp15
%tmp18 = icmp sgt i32 %local_6_.us.postloop, 82
br i1 %tmp18, label %bci_90.postloop, label %not_zero65.us.postloop.1
bci_90.postloop: ; preds = %not_zero65.us.postloop
%tmp19 = icmp sgt i64 %indvars.iv180.postloop, 68
br i1 %tmp19, label %bci_127.unr-lcssa, label %bci_55.postloop
not_zero65.us.postloop.1: ; preds = %not_zero65.us.postloop
%tmp20 = mul i32 %tmp7, %tmp17
%tmp21 = mul i32 %tmp20, %tmp17
%tmp22 = mul i32 %tmp7, %tmp21
%tmp23 = mul i32 %tmp22, %tmp21
%tmp24 = mul i32 %tmp7, %tmp23
%tmp25 = mul i32 %tmp24, %tmp23
%tmp26 = mul i32 %tmp7, %tmp25
%tmp27 = mul i32 %tmp26, %tmp25
%tmp28 = mul i32 %tmp7, %tmp27
%tmp29 = mul i32 %tmp28, %tmp27
%tmp30 = mul i32 %tmp7, %tmp29
%tmp31 = mul i32 %tmp30, %tmp29
%tmp32 = mul i32 %tmp7, %tmp31
%tmp33 = mul i32 %tmp32, %tmp31
%tmp34 = mul i32 %tmp7, %tmp33
%tmp35 = mul i32 %tmp34, %tmp33
%tmp36 = mul i32 %tmp7, %tmp35
%tmp37 = mul i32 %tmp36, %tmp35
%tmp38 = mul i32 %tmp7, %tmp37
%tmp39 = mul i32 %tmp38, %tmp37
%tmp40 = mul i32 %tmp7, %tmp39
%tmp41 = mul i32 %tmp40, %tmp39
%tmp42 = mul i32 %tmp7, %tmp41
%tmp43 = mul i32 %tmp42, %tmp41
%tmp44 = mul i32 %tmp7, %tmp43
%tmp45 = mul i32 %tmp44, %tmp43
%tmp46 = mul i32 %tmp7, %tmp45
%tmp47 = mul i32 %tmp46, %tmp45
%tmp48 = mul i32 %tmp7, %tmp47
%tmp49 = mul i32 %tmp48, %tmp47
%tmp50 = add nsw i32 %local_6_.us.postloop, 20
br label %not_zero65.us.postloop
}