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[ConstantFolding] Fix to prevent constant folding having to repeatedly scan operands. NFCI 

After the loop unroll threshold was increased in r295538, very
large constant expressions can be created. This prevents them
from having to be recursively scanned, leading to a compile
time blow-up.

Differential Revision: https://reviews.llvm.org/D30689

llvm-svn: 298356
This commit is contained in:
David Green 2017-03-21 10:17:39 +00:00
parent 57db7c6860
commit da21170c49
2 changed files with 74 additions and 1 deletions
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2
llvm/lib/Analysis/ConstantFolding.cpp
View File

@ -1058,8 +1058,8 @@ ConstantFoldConstantImpl(const Constant *C, const DataLayout &DL,
if (It == FoldedOps.end()) {
if (auto *FoldedC =
ConstantFoldConstantImpl(NewC, DL, TLI, FoldedOps)) {
NewC = FoldedC;
FoldedOps.insert({NewC, FoldedC});
NewC = FoldedC;
} else {
FoldedOps.insert({NewC, NewC});
}

73
llvm/test/Analysis/ConstantFolding/timeout.ll Normal file
View File

@ -0,0 +1,73 @@
; NOTE: This is a timeout test for some O(something silly) constant folding behaviour. It may not be the best test. Providing it finishes, it passes.
; RUN: opt < %s -O3 -S | FileCheck %s
target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
target triple = "armv8-none-eabi"
%struct.ST = type { %struct.ST* }
@global = internal global [121 x i8] zeroinitializer, align 1
define void @func() #0 {
;CHECK-LABEL: func
entry:
%s = alloca %struct.ST*, align 4
%j = alloca i32, align 4
store %struct.ST* bitcast ([121 x i8]* @global to %struct.ST*), %struct.ST** %s, align 4
store i32 0, i32* %j, align 4
br label %for.cond
for.cond: ; preds = %for.inc, %entry
%0 = load i32, i32* %j, align 4
%cmp = icmp slt i32 %0, 30
br i1 %cmp, label %for.body, label %for.end
for.body: ; preds = %for.cond
%1 = load %struct.ST*, %struct.ST** %s, align 4
%2 = bitcast %struct.ST* %1 to i8*
%add.ptr = getelementptr inbounds i8, i8* %2, i32 4
%3 = ptrtoint i8* %add.ptr to i32
%4 = load %struct.ST*, %struct.ST** %s, align 4
%5 = bitcast %struct.ST* %4 to i8*
%add.ptr1 = getelementptr inbounds i8, i8* %5, i32 4
%6 = ptrtoint i8* %add.ptr1 to i32
%rem = urem i32 %6, 2
%cmp2 = icmp eq i32 %rem, 0
br i1 %cmp2, label %cond.true, label %cond.false
cond.true: ; preds = %for.body
br label %cond.end
cond.false: ; preds = %for.body
%7 = load %struct.ST*, %struct.ST** %s, align 4
%8 = bitcast %struct.ST* %7 to i8*
%add.ptr3 = getelementptr inbounds i8, i8* %8, i32 4
%9 = ptrtoint i8* %add.ptr3 to i32
%rem4 = urem i32 %9, 2
br label %cond.end
cond.end: ; preds = %cond.false, %cond.true
%cond = phi i32 [ 0, %cond.true ], [ %rem4, %cond.false ]
%add = add i32 %3, %cond
%10 = inttoptr i32 %add to %struct.ST*
%11 = load %struct.ST*, %struct.ST** %s, align 4
%next = getelementptr inbounds %struct.ST, %struct.ST* %11, i32 0, i32 0
store %struct.ST* %10, %struct.ST** %next, align 4
%12 = load %struct.ST*, %struct.ST** %s, align 4
%next5 = getelementptr inbounds %struct.ST, %struct.ST* %12, i32 0, i32 0
%13 = load %struct.ST*, %struct.ST** %next5, align 4
store %struct.ST* %13, %struct.ST** %s, align 4
br label %for.inc
for.inc: ; preds = %cond.end
%14 = load i32, i32* %j, align 4
%inc = add nsw i32 %14, 1
store i32 %inc, i32* %j, align 4
br label %for.cond
for.end: ; preds = %for.cond
%15 = load %struct.ST*, %struct.ST** %s, align 4
%next6 = getelementptr inbounds %struct.ST, %struct.ST* %15, i32 0, i32 0
store %struct.ST* null, %struct.ST** %next6, align 4
ret void
}