2015-10-06 23:36:44 +08:00
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; RUN: opt -S %loadPolly -polly-dependences \
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2015-08-28 00:55:18 +08:00
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; RUN: -analyze < %s | FileCheck %s
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2016-06-27 22:47:38 +08:00
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; RUN: opt -S %loadPolly -polly-function-dependences \
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; RUN: -analyze < %s | FileCheck %s -check-prefix=FUNC
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2015-08-02 21:30:33 +08:00
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; CHECK: RAW dependences:
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; CHECK: { Stmt_bb9[0] -> Stmt_bb10[0] }
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; CHECK: WAR dependences:
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[Polly] [DependenceInfo] change WAR, WAW generation to correct semantics
= Change of WAR, WAW generation: =
- `buildFlow(Sink, MustSource, MaySource, Sink)` treates any flow of the form
`sink <- may source <- must source` as a *may* dependence.
- we used to call:
```lang=cpp, name=old-flow-call.cpp
Flow = buildFlow(MustWrite, MustWrite, Read, Schedule);
WAW = isl_union_flow_get_must_dependence(Flow);
WAR = isl_union_flow_get_may_dependence(Flow);
```
- This caused some WAW dependences to be treated as WAR dependences.
- Incorrect semantics.
- Now, we call WAR and WAW correctly.
== Correct WAW: ==
```lang=cpp, name=new-waw-call.cpp
Flow = buildFlow(Write, MustWrite, MayWrite, Schedule);
WAW = isl_union_flow_get_may_dependence(Flow);
isl_union_flow_free(Flow);
```
== Correct WAR: ==
```lang=cpp, name=new-war-call.cpp
Flow = buildFlow(Write, Read, MustaWrite, Schedule);
WAR = isl_union_flow_get_must_dependence(Flow);
isl_union_flow_free(Flow);
```
- We want the "shortest" WAR possible (exact dependences).
- We mark all the *must-writes* as may-source, reads as must-souce.
- Then, we ask for *must* dependence.
- This removes all the reads that flow through a *must-write*
before reaching a sink.
- Note that we only block ealier writes with *must-writes*. This is
intuitively correct, as we do not want may-writes to block
must-writes.
- Leaves us with direct (R -> W).
- This affects reduction generation since RED is built using WAW and WAR.
= New StrictWAW for Reductions: =
- We used to call:
```lang=cpp,name=old-waw-war-call.cpp
Flow = buildFlow(MustWrite, MustWrite, Read, Schedule);
WAW = isl_union_flow_get_must_dependence(Flow);
WAR = isl_union_flow_get_may_dependence(Flow);
```
- This *is* the right model of WAW we need for reductions, just not in general.
- Reductions need to track only *strict* WAW, without any interfering reductions.
= Explanation: Why the new WAR dependences in tests are correct: =
- We no longer set WAR = WAR - WAW
- Hence, we will have WAR dependences that were originally removed.
- These may look incorrect, but in fact make sense.
== Code: ==
```lang=llvm, name=new-war-dependence.ll
; void manyreductions(long *A) {
; for (long i = 0; i < 1024; i++)
; for (long j = 0; j < 1024; j++)
; S0: *A += 42;
;
; for (long i = 0; i < 1024; i++)
; for (long j = 0; j < 1024; j++)
; S1: *A += 42;
;
```
=== WAR dependence: ===
{ S0[1023, 1023] -> S1[0, 0] }
- Between `S0[1023, 1023]` and `S1[0, 0]`, we will have the dependences:
```lang=cpp, name=dependence-incorrect, counterexample
S0[1023, 1023]:
*-- tmp = *A (load0)--*
WAR 2 add = tmp + 42 |
*-> *A = add (store0) |
WAR 1
S1[0, 0]: |
tmp = *A (load1) |
add = tmp + 42 |
A = add (store1)<-*
```
- One may assume that WAR2 *hides* WAR1 (since store0 happens before
store1). However, within a statement, Polly has no idea about the
ordering of loads and stores.
- Hence, according to Polly, the code may have looked like this:
```lang=cpp, name=dependence-correct
S0[1023, 1023]:
A = add (store0)
tmp = A (load0) ---*
add = A + 42 |
WAR 1
S1[0, 0]: |
tmp = A (load1) |
add = A + 42 |
A = add (store1) <-*
```
- So, Polly generates (correct) WAR dependences. It does not make sense
to remove these dependences, since they are correct with respect to
Polly's model.
Reviewers: grosser, Meinersbur
tags: #polly
Differential revision: https://reviews.llvm.org/D31386
llvm-svn: 299429
2017-04-04 21:08:23 +08:00
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; CHECK: { Stmt_bb3[0] -> Stmt_bb10[0] }
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2015-11-04 00:54:49 +08:00
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; CHECK: WAW dependences:
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; CHECK: { Stmt_bb3[0] -> Stmt_bb10[0] }
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2015-08-02 21:30:33 +08:00
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; CHECK: Reduction dependences:
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; CHECK: { }
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2016-06-27 22:47:38 +08:00
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; FUNC: RAW dependences:
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2017-05-03 15:57:35 +08:00
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; FUNC-NEXT: { Stmt_bb9[0] -> Stmt_bb10[0]; [Stmt_bb9[0] -> Stmt_bb9_Write0[]] -> [Stmt_bb10[0] -> Stmt_bb10_Read0[]] }
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2016-06-27 22:47:38 +08:00
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; FUNC-NEXT: WAR dependences:
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2017-07-04 23:54:11 +08:00
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; FUNC-NEXT: { [Stmt_bb3[0] -> Stmt_bb3_Read0[]] -> [Stmt_bb10[0] -> Stmt_bb10_Write1[]]; Stmt_bb3[0] -> Stmt_bb10[0] }
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2016-06-27 22:47:38 +08:00
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; FUNC-NEXT: WAW dependences:
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2017-05-03 15:57:35 +08:00
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; FUNC-NEXT: { Stmt_bb3[0] -> Stmt_bb10[0]; [Stmt_bb3[0] -> Stmt_bb3_Write1[]] -> [Stmt_bb10[0] -> Stmt_bb10_Write1[]] }
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2016-06-27 22:47:38 +08:00
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; FUNC-NEXT: Reduction dependences:
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; FUNC-NEXT: { }
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2015-08-02 21:30:33 +08:00
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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define void @hoge(i32 %arg, [1024 x double]* %arg1) {
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bb:
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br label %bb2
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bb2: ; preds = %bb
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br label %bb3
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bb3: ; preds = %bb10, %bb2
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%tmp = phi i64 [ 0, %bb10 ], [ 0, %bb2 ]
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%tmp4 = icmp sgt i32 %arg, 0
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%tmp5 = getelementptr inbounds [1024 x double], [1024 x double]* %arg1, i64 0, i64 0
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%tmp6 = load double, double* %tmp5, align 8
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%tmp7 = fadd double undef, %tmp6
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2015-11-04 00:54:49 +08:00
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store double %tmp7, double* %tmp5, align 8
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2015-08-02 21:30:33 +08:00
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br i1 false, label %bb8, label %bb9
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bb8: ; preds = %bb3
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br label %bb10
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bb9: ; preds = %bb3
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br label %bb10
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bb10: ; preds = %bb9, %bb8
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%tmp11 = phi double [ undef, %bb8 ], [ undef, %bb9 ]
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%tmp12 = getelementptr inbounds [1024 x double], [1024 x double]* %arg1, i64 %tmp, i64 0
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store double %tmp11, double* %tmp12, align 8
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%tmp13 = add nuw nsw i64 0, 1
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%tmp14 = trunc i64 %tmp13 to i32
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br i1 false, label %bb3, label %bb15
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bb15: ; preds = %bb10
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br label %bb16
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bb16: ; preds = %bb15
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ret void
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}
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