Commit f8b1c252 authored by Hans Wennborg's avatar Hans Wennborg
Browse files

Merging r370720 and r370721: 

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r370720 | bjope | 2019-09-03 11:33:40 +0200 (Tue, 03 Sep 2019) | 13 lines

[LV] Precommit test case showing miscompile from PR43166. NFC

Summary:  Precommit test case showing miscompile from PR43166.

Reviewers: fhahn, Ayal

Reviewed By: fhahn

Subscribers: rkruppe, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67072
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r370721 | bjope | 2019-09-03 11:33:55 +0200 (Tue, 03 Sep 2019) | 20 lines

[LV] Fix miscompiles by adding non-header PHI nodes to AllowedExit

Summary:
Fold-tail currently supports reduction last-vector-value live-out's,
but has yet to support last-scalar-value live-outs, including
non-header phi's. As it relies on AllowedExit in order to detect
them and bail out we need to add the non-header PHI nodes to
AllowedExit, otherwise we end up with miscompiles.

Solves https://bugs.llvm.org/show_bug.cgi?id=43166

Reviewers: fhahn, Ayal

Reviewed By: fhahn, Ayal

Subscribers: anna, hiraditya, rkruppe, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67074
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llvm-svn: 371044
parent 5a661d61

llvm/include/llvm/Transforms/Vectorize/LoopVectorizationLegality.h

+2 −2
Original line number Diff line number Diff line
@@ -452,8 +452,8 @@ private: 
  /// Holds the widest induction type encountered.

  Type *WidestIndTy = nullptr;



  /// Allowed outside users. This holds the induction and reduction

  /// vars which can be accessed from outside the loop.

  /// Allowed outside users. This holds the variables that can be accessed from

  /// outside the loop.

  SmallPtrSet<Value *, 4> AllowedExit;



  /// Can we assume the absence of NaNs.

llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp

+1 −0
Original line number Diff line number Diff line
@@ -631,6 +631,7 @@ bool LoopVectorizationLegality::canVectorizeInstrs() { 
          // Unsafe cyclic dependencies with header phis are identified during

          // legalization for reduction, induction and first order

          // recurrences.

          AllowedExit.insert(&I);

          continue;

        }

llvm/test/Transforms/LoopVectorize/pr43166-fold-tail-by-masking.ll

0 → 100644
+165 −0
Original line number Diff line number Diff line 
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py

; RUN: opt < %s -loop-vectorize -force-vector-width=4 -S | FileCheck %s





; Test cases below are reduced (and slightly modified) reproducers based on a

; problem seen when compiling a C program like this:

;

;    #include <stdint.h>

;    #include <stdio.h>

;

;    int y = 0;

;    int b = 1;

;    int d = 1;

;

;    int main() {

;      #pragma clang loop vectorize_width(4)

;      for (int i = 0; i < 3; ++i) {

;        b = (y == 0) ? d : (d / y);

;      }

;

;      if (b == 1)

;        printf("GOOD!\n");

;      else

;        printf("BAD!\n");

;    }

;

; When compiled+executed using

;    build-all/bin/clang -O1 lv-bug.c && ./a.out

; the result is "GOOD!"

;

; When compiled+executed using

;    build-all/bin/clang -O1 lv-bug.c -fvectorize && ./a.out

; the result is "BAD!"





; This test case miscompiled with clang 8.0.0 (see PR43166), now we get

;   loop not vectorized: Cannot fold tail by masking in the presence of live outs.

; instead.

define i64 @test1(i64 %y) {

; CHECK-LABEL: @test1(

; CHECK-NEXT:  entry:

; CHECK-NEXT:    br label [[FOR_BODY:%.*]]

; CHECK:       for.body:

; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[INC:%.*]], [[COND_END:%.*]] ]

; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 [[Y:%.*]], 0

; CHECK-NEXT:    br i1 [[CMP]], label [[COND_END]], label [[COND_FALSE:%.*]]

; CHECK:       cond.false:

; CHECK-NEXT:    [[DIV:%.*]] = xor i64 3, [[Y]]

; CHECK-NEXT:    br label [[COND_END]]

; CHECK:       cond.end:

; CHECK-NEXT:    [[COND:%.*]] = phi i64 [ [[DIV]], [[COND_FALSE]] ], [ 77, [[FOR_BODY]] ]

; CHECK-NEXT:    [[INC]] = add nuw nsw i32 [[I]], 1

; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp eq i32 [[INC]], 3

; CHECK-NEXT:    br i1 [[EXITCOND]], label [[FOR_COND_CLEANUP:%.*]], label [[FOR_BODY]]

; CHECK:       for.cond.cleanup:

; CHECK-NEXT:    [[COND_LCSSA:%.*]] = phi i64 [ [[COND]], [[COND_END]] ]

; CHECK-NEXT:    ret i64 [[COND_LCSSA]]

;

entry:

  br label %for.body



for.body:

  %i = phi i32 [ 0, %entry ], [ %inc, %cond.end ]

  %cmp = icmp eq i64 %y, 0

  br i1 %cmp, label %cond.end, label %cond.false



cond.false:

  %div = xor i64 3, %y

  br label %cond.end



cond.end:

  %cond = phi i64 [ %div, %cond.false ], [ 77, %for.body ]

  %inc = add nuw nsw i32 %i, 1

  %exitcond = icmp eq i32 %inc, 3

  br i1 %exitcond, label %for.cond.cleanup, label %for.body



for.cond.cleanup:

  ret i64 %cond

}



; This test case miscompiled with clang 8.0.0 (see PR43166), now we get

;   loop not vectorized: Cannot fold tail by masking in the presence of live outs.

; instead.

define i64 @test2(i64 %y) {

; CHECK-LABEL: @test2(

; CHECK-NEXT:  entry:

; CHECK-NEXT:    br label [[FOR_BODY:%.*]]

; CHECK:       for.body:

; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[INC:%.*]], [[COND_END:%.*]] ]

; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 [[Y:%.*]], 0

; CHECK-NEXT:    br i1 [[CMP]], label [[COND_END]], label [[COND_FALSE:%.*]]

; CHECK:       cond.false:

; CHECK-NEXT:    br label [[COND_END]]

; CHECK:       cond.end:

; CHECK-NEXT:    [[COND:%.*]] = phi i64 [ 55, [[COND_FALSE]] ], [ 77, [[FOR_BODY]] ]

; CHECK-NEXT:    [[INC]] = add nuw nsw i32 [[I]], 1

; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp eq i32 [[INC]], 3

; CHECK-NEXT:    br i1 [[EXITCOND]], label [[FOR_COND_CLEANUP:%.*]], label [[FOR_BODY]]

; CHECK:       for.cond.cleanup:

; CHECK-NEXT:    [[COND_LCSSA:%.*]] = phi i64 [ [[COND]], [[COND_END]] ]

; CHECK-NEXT:    ret i64 [[COND_LCSSA]]

;

entry:

  br label %for.body



for.body:

  %i = phi i32 [ 0, %entry ], [ %inc, %cond.end ]

  %cmp = icmp eq i64 %y, 0

  br i1 %cmp, label %cond.end, label %cond.false



cond.false:

  br label %cond.end



cond.end:

  %cond = phi i64 [ 55, %cond.false ], [ 77, %for.body ]

  %inc = add nuw nsw i32 %i, 1

  %exitcond = icmp eq i32 %inc, 3

  br i1 %exitcond, label %for.cond.cleanup, label %for.body



for.cond.cleanup:

  ret i64 %cond

}



; This test case miscompiled with clang 8.0.0 (see PR43166), now we get

;   loop not vectorized: Cannot fold tail by masking in the presence of live outs.

; instead.

define i32 @test3(i64 %y) {

; CHECK-LABEL: @test3(

; CHECK-NEXT:  entry:

; CHECK-NEXT:    br label [[FOR_BODY:%.*]]

; CHECK:       for.body:

; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[INC:%.*]], [[COND_END:%.*]] ]

; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 [[Y:%.*]], 0

; CHECK-NEXT:    br i1 [[CMP]], label [[COND_END]], label [[COND_FALSE:%.*]]

; CHECK:       cond.false:

; CHECK-NEXT:    br label [[COND_END]]

; CHECK:       cond.end:

; CHECK-NEXT:    [[COND:%.*]] = phi i32 [ 55, [[COND_FALSE]] ], [ [[I]], [[FOR_BODY]] ]

; CHECK-NEXT:    [[INC]] = add nuw nsw i32 [[I]], 1

; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp eq i32 [[INC]], 3

; CHECK-NEXT:    br i1 [[EXITCOND]], label [[FOR_COND_CLEANUP:%.*]], label [[FOR_BODY]]

; CHECK:       for.cond.cleanup:

; CHECK-NEXT:    [[COND_LCSSA:%.*]] = phi i32 [ [[COND]], [[COND_END]] ]

; CHECK-NEXT:    ret i32 [[COND_LCSSA]]

;

entry:

  br label %for.body



for.body:

  %i = phi i32 [ 0, %entry ], [ %inc, %cond.end ]

  %cmp = icmp eq i64 %y, 0

  br i1 %cmp, label %cond.end, label %cond.false



cond.false:

  br label %cond.end



cond.end:

  %cond = phi i32 [ 55, %cond.false ], [ %i, %for.body ]

  %inc = add nuw nsw i32 %i, 1

  %exitcond = icmp eq i32 %inc, 3

  br i1 %exitcond, label %for.cond.cleanup, label %for.body



for.cond.cleanup:

  ret i32 %cond

}