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[Hexagon] Handle long-running simplification loop in idiom recognition

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The initial assumption was that the simplification would converge to a
fixed point relatvely quickly. Turns out that there are legitimate situa-
tions where the complexity of the code causes it to take a large number
of iterations.

Two main changes:
- Instead of aborting upon hitting the limit, simply return nullptr.
- Reduce the limit to 10,000 from 100,000.

llvm-svn: 304441
This commit is contained in:
Krzysztof Parzyszek 2017-06-01 18:00:47 +00:00
parent 9d4440780e
commit 8acfcfafc3
2 changed files with 67 additions and 3 deletions
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8
lib/Target/Hexagon/HexagonLoopIdiomRecognition.cpp
View File

@ -59,6 +59,9 @@ cl::opt<bool> HexagonVolatileMemcpy("disable-hexagon-volatile-memcpy",
cl::Hidden, cl::init(false),
cl::desc("Enable Hexagon-specific memcpy for volatile destination."));
static cl::opt<unsigned> SimplifyLimit("hlir-simplify-limit", cl::init(10000),
cl::Hidden, cl::desc("Maximum number of simplification steps in HLIR"));
static const char *HexagonVolatileMemcpyName
= "hexagon_memcpy_forward_vp4cp4n2";
@ -477,7 +480,7 @@ Value *Simplifier::simplify(Context &C) {
WorkListType Q;
Q.push_back(C.Root);
unsigned Count = 0;
const unsigned Limit = 100000;
const unsigned Limit = SimplifyLimit;
while (!Q.empty()) {
if (Count++ >= Limit)
@ -501,8 +504,7 @@ Value *Simplifier::simplify(Context &C) {
Q.push_back(Op);
}
}
assert(Count < Limit && "Infinite loop in HLIR/simplify?");
return C.Root;
return Count < Limit ? C.Root : nullptr;
}

62
test/CodeGen/Hexagon/loop-idiom/pmpy-long-loop.ll Normal file
View File

@ -0,0 +1,62 @@
; RUN: opt -march=hexagon -hexagon-loop-idiom -S < %s | FileCheck %s
;
; The number of nested selects caused the simplification loop to take
; more than the maximum number of iterations. This caused the compiler
; to crash under suspicion of an infinite loop. This (still reduced)
; testcase shows a legitimate case where this limit was exceeded.
; Instead of crashing, gracefully abort the simplification.
;
; Check for sane output.
; CHECK: define void @fred
target datalayout = "e-m:e-p:32:32:32-a:0-n16:32-i64:64:64-i32:32:32-i16:16:16-i1:8:8-f32:32:32-f64:64:64-v32:32:32-v64:64:64-v512:512:512-v1024:1024:1024-v2048:2048:2048"
target triple = "hexagon"
define void @fred() unnamed_addr #0 {
b0:
%v1 = select i1 false, i32 undef, i32 2
br label %b2
b2: ; preds = %b2, %b0
%v3 = sext i16 undef to i32
%v4 = add nsw i32 %v1, %v3
%v5 = select i1 undef, i32 undef, i32 %v4
%v6 = icmp slt i32 %v5, undef
%v7 = select i1 %v6, i32 %v5, i32 undef
%v8 = icmp slt i32 %v7, 0
%v9 = select i1 %v8, i32 %v7, i32 0
%v10 = sub i32 undef, undef
%v11 = add i32 %v10, %v9
%v12 = sext i16 undef to i32
%v13 = sext i16 undef to i32
%v14 = add nsw i32 %v1, %v13
%v15 = select i1 undef, i32 undef, i32 %v14
%v16 = icmp slt i32 %v15, undef
%v17 = select i1 %v16, i32 %v15, i32 undef
%v18 = select i1 undef, i32 %v17, i32 %v12
%v19 = add i32 undef, %v18
%v20 = sext i16 undef to i32
%v21 = sext i16 0 to i32
%v22 = add nsw i32 %v1, %v21
%v23 = sext i16 undef to i32
%v24 = add nsw i32 %v1, %v23
%v25 = select i1 undef, i32 undef, i32 %v24
%v26 = icmp slt i32 %v25, %v22
%v27 = select i1 %v26, i32 %v25, i32 %v22
%v28 = icmp slt i32 %v27, %v20
%v29 = select i1 %v28, i32 %v27, i32 %v20
%v30 = add i32 undef, %v29
%v31 = add i32 %v11, undef
%v32 = add i32 %v31, undef
%v33 = add i32 %v32, %v19
%v34 = add i32 %v33, %v30
%v35 = add nsw i32 %v34, 32768
%v36 = icmp ult i32 %v35, 65536
%v37 = select i1 %v36, i32 %v34, i32 undef
br i1 undef, label %b2, label %b38
b38: ; preds = %b2
unreachable
}
attributes #0 = { "target-cpu"="hexagonv60" }