[llvm] r235311 - Recognize n/1 in the SCEV divide function

[Nick Lewycky]

Brendon Cahoon wrote:
> Author: bcahoon
> Date: Mon Apr 20 11:03:28 2015
> New Revision: 235311
>
> URL: http://llvm.org/viewvc/llvm-project?rev=235311&view=rev
> Log:
> Recognize n/1 in the SCEV divide function
>
> n/1 generates a quotient equal to n and a remainder of 0.
> If this case is not recognized, then the SCEV divide() function
> can return a remainder that is greater than or equal to the
> denominator, which means the delinearized subscripts for the
> test case will be incorrect.

Wait, this is needed for correctness? Are you sure this isn't papering 
over a bug in the divide() code?

> Differential Revision: http://reviews.llvm.org/D9003
>
> Added:
>      llvm/trunk/test/Analysis/Delinearization/divide_by_one.ll
> Modified:
>      llvm/trunk/lib/Analysis/ScalarEvolution.cpp
>
> Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=235311&r1=235310&r2=235311&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
> +++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Mon Apr 20 11:03:28 2015
> @@ -726,6 +726,13 @@ public:
>         return;
>       }
>
> +    // A simple case when N/1. The quotient is N.
> +    if (Denominator->isOne()) {
> +      *Quotient = Numerator;
> +      *Remainder = D.Zero;
> +      return;
> +    }
> +
>       // Split the Denominator when it is a product.
>       if (const SCEVMulExpr *T = dyn_cast<const SCEVMulExpr>(Denominator)) {
>         const SCEV *Q, *R;
>
> Added: llvm/trunk/test/Analysis/Delinearization/divide_by_one.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/Delinearization/divide_by_one.ll?rev=235311&view=auto
> ==============================================================================
> --- llvm/trunk/test/Analysis/Delinearization/divide_by_one.ll (added)
> +++ llvm/trunk/test/Analysis/Delinearization/divide_by_one.ll Mon Apr 20 11:03:28 2015
> @@ -0,0 +1,70 @@
> +; RUN: opt<  %s -analyze -delinearize | FileCheck %s
> +
> +target datalayout = "e-m:e-p:32:32-i1:32-i64:64-a:0-n32"
> +
> +; Check that division by 1 can be delinearized.
> +;
> +; void test1(unsigned char *dst, int stride, int bs) {
> +;   for (int r = bs; r>= 0; --r)
> +;     for (int c = 0; c<  bs; ++c)
> +;       dst[r * stride + c] = dst[(r + 1) * stride + c - 1];
> +; }
> +
> +; AddRec: {{(-1 + ((1 + %bs) * %stride)),+,(-1 * %stride)}<%for.cond1.preheader>,+,1}<nw><%for.body3>
> +; CHECK: Inst:  %0 = load i8, i8* %arrayidx, align 1
> +; CHECK: Base offset: %dst
> +; CHECK: ArrayDecl[UnknownSize][%stride] with elements of 1 bytes.
> +; CHECK: ArrayRef[{(1 + %bs),+,-1}<nw><%for.cond1.preheader>][{-1,+,1}<nw><%for.body3>]
> +
> +; AddRec: {{(%stride * %bs),+,(-1 * %stride)}<%for.cond1.preheader>,+,1}<nw><%for.body3>
> +; CHECK: Inst:  store i8 %0, i8* %arrayidx7, align 1
> +; CHECK: Base offset: %dst
> +; CHECK: ArrayDecl[UnknownSize][%stride] with elements of 1 bytes.
> +; CHECK: ArrayRef[{%bs,+,-1}<nsw><%for.cond1.preheader>][{0,+,1}<nuw><nsw><%for.body3>]
> +
> +define void @test(i8* nocapture %dst, i32 %stride, i32 %bs) {
> +entry:
> +  %cmp20 = icmp sgt i32 %bs, -1
> +  br i1 %cmp20, label %for.cond1.preheader.lr.ph, label %for.end9
> +
> +for.cond1.preheader.lr.ph:
> +  %cmp218 = icmp slt i32 0, %bs
> +  br label %for.cond1.preheader
> +
> +for.cond1.preheader:
> +  %r.021 = phi i32 [ %bs, %for.cond1.preheader.lr.ph ], [ %dec, %for.inc8 ]
> +  br i1 %cmp218, label %for.body3.lr.ph, label %for.inc8
> +
> +for.body3.lr.ph:
> +  %add = add nsw i32 %r.021, 1
> +  %mul = mul nsw i32 %add, %stride
> +  %add4 = add i32 %mul, -1
> +  %mul5 = mul nsw i32 %r.021, %stride
> +  br label %for.body3
> +
> +for.body3:
> +  %c.019 = phi i32 [ 0, %for.body3.lr.ph ], [ %inc, %for.body3 ]
> +  %sub = add i32 %add4, %c.019
> +  %arrayidx = getelementptr inbounds i8, i8* %dst, i32 %sub
> +  %0 = load i8, i8* %arrayidx, align 1
> +  %add6 = add nsw i32 %c.019, %mul5
> +  %arrayidx7 = getelementptr inbounds i8, i8* %dst, i32 %add6
> +  store i8 %0, i8* %arrayidx7, align 1
> +  %inc = add nsw i32 %c.019, 1
> +  %cmp2 = icmp slt i32 %inc, %bs
> +  br i1 %cmp2, label %for.body3, label %for.cond1.for.inc8_crit_edge
> +
> +for.cond1.for.inc8_crit_edge:
> +  br label %for.inc8
> +
> +for.inc8:
> +  %dec = add nsw i32 %r.021, -1
> +  %cmp = icmp sgt i32 %dec, -1
> +  br i1 %cmp, label %for.cond1.preheader, label %for.cond.for.end9_crit_edge
> +
> +for.cond.for.end9_crit_edge:
> +  br label %for.end9
> +
> +for.end9:
> +  ret void
> +}
>
>
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