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

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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



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298356 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Green 2017-03-21 10:17:39 +00:00
parent de5c0c25c0
commit 8b2132abbe
2 changed files with 74 additions and 1 deletions
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2
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
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
}