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[LV/LoopAccesses] Backward dependences are not safe just because the

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accesses are via different types

Noticed this while generalizing the code for loop distribution.

I confirmed with Arnold that this was indeed a bug and managed to create
a testcase.

llvm-svn: 230647
This commit is contained in:
Adam Nemet 2015-02-26 17:58:48 +00:00
parent ab0488f5cd
commit f117878f33
2 changed files with 52 additions and 2 deletions
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4
lib/Analysis/LoopAccessAnalysis.cpp
View File

@ -794,11 +794,10 @@ bool MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
assert(Val.isStrictlyPositive() && "Expect a positive value");
// Positive distance bigger than max vectorization factor.
if (ATy != BTy) {
DEBUG(dbgs() <<
"LAA: ReadWrite-Write positive dependency with different types\n");
return false;
return true;
}
unsigned Distance = (unsigned) Val.getZExtValue();
@ -820,6 +819,7 @@ bool MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
return true;
}
// Positive distance bigger than max vectorization factor.
MaxSafeDepDistBytes = Distance < MaxSafeDepDistBytes ?
Distance : MaxSafeDepDistBytes;

50
test/Analysis/LoopAccessAnalysis/backward-dep-different-types.ll Normal file
View File

@ -0,0 +1,50 @@
; RUN: opt -loop-accesses -analyze < %s | FileCheck %s
; In this loop just because we access A through different types (int, float)
; we still have a dependence cycle:
;
; for (i = 0; i < n; i++) {
; A_float = (float *) A;
; A_float[i + 1] = A[i] * B[i];
; }
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.10.0"
; CHECK: Report: unsafe dependent memory operations in loop
; CHECK-NOT: Memory dependences are safe
@n = global i32 20, align 4
@B = common global i32* null, align 8
@A = common global i32* null, align 8
define void @f() {
entry:
%a = load i32** @A, align 8
%b = load i32** @B, align 8
br label %for.body
for.body: ; preds = %for.body, %entry
%storemerge3 = phi i64 [ 0, %entry ], [ %add, %for.body ]
%arrayidxA = getelementptr inbounds i32* %a, i64 %storemerge3
%loadA = load i32* %arrayidxA, align 2
%arrayidxB = getelementptr inbounds i32* %b, i64 %storemerge3
%loadB = load i32* %arrayidxB, align 2
%mul = mul i32 %loadB, %loadA
%add = add nuw nsw i64 %storemerge3, 1
%a_float = bitcast i32* %a to float*
%arrayidxA_plus_2 = getelementptr inbounds float* %a_float, i64 %add
%mul_float = sitofp i32 %mul to float
store float %mul_float, float* %arrayidxA_plus_2, align 2
%exitcond = icmp eq i64 %add, 20
br i1 %exitcond, label %for.end, label %for.body
for.end: ; preds = %for.body
ret void
}