From c8ce9e59a883f452bc538b5f16fb83649472dc3e Mon Sep 17 00:00:00 2001

From: Keno Fischer <kfischer@college.harvard.edu>

Date: Wed, 13 Jul 2016 01:28:12 +0000

Subject: [PATCH] Fix ScalarEvolutionExpander step scaling bug

The expandAddRecExprLiterally function incorrectly transforms

`[Start + Step * X]` into `Step * [Start + X]` instead of the correct

transform of `[Step * X] + Start`.

This caused https://github.com/JuliaLang/julia/issues/14704#issuecomment-174126219

due to what appeared to be sufficiently complicated loop interactions.

Patch by Jameson Nash (jameson@juliacomputing.com).

Reviewers: sanjoy

Differential Revision: http://reviews.llvm.org/D16505

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275239 91177308-0d34-0410-b5e6-96231b3b80d8

Alpine maintainer notes:

This patch replaces deps/patches/llvm-3.7.1_3.patch from Julia.

---

 lib/Analysis/ScalarEvolutionExpander.cpp           |  7 ++++

 .../ScalarEvolution/incorrect-offset-scaling.ll    | 48 ++++++++++++++++++++++

 2 files changed, 55 insertions(+)

 create mode 100644 test/Analysis/ScalarEvolution/incorrect-offset-scaling.ll

diff --git a/lib/Analysis/ScalarEvolutionExpander.cpp b/lib/Analysis/ScalarEvolutionExpander.cpp

index 7716435..77e4ec7 100644

--- a/lib/Analysis/ScalarEvolutionExpander.cpp

+++ b/lib/Analysis/ScalarEvolutionExpander.cpp

@@ -1288,6 +1288,13 @@ Value *SCEVExpander::expandAddRecExprLiterally(const SCEVAddRecExpr *S) {

   if (!SE.dominates(Step, L->getHeader())) {

     PostLoopScale = Step;

     Step = SE.getConstant(Normalized->getType(), 1);

+    if (!Start->isZero()) {

+        // The normalization below assumes that Start is constant zero, so if

+        // it isn't re-associate Start to PostLoopOffset.

+        assert(!PostLoopOffset && "Start not-null but PostLoopOffset set?");

+        PostLoopOffset = Start;

+        Start = SE.getConstant(Normalized->getType(), 0);

+    }

     Normalized =

       cast<SCEVAddRecExpr>(SE.getAddRecExpr(

                              Start, Step, Normalized->getLoop(),

diff --git a/test/Analysis/ScalarEvolution/incorrect-offset-scaling.ll b/test/Analysis/ScalarEvolution/incorrect-offset-scaling.ll

new file mode 100644

index 0000000..7ffb093

--- /dev/null

+++ b/test/Analysis/ScalarEvolution/incorrect-offset-scaling.ll

@@ -0,0 +1,48 @@

+; RUN: opt -S -loop-reduce < %s | FileCheck %s

+

+target triple = "x86_64-unknown-unknown"

+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"

+

+define void @incorrect_offset_scaling(i64, i64*) {

+top:

+  br label %L

+

+L:                                                ; preds = %idxend.10, %idxend, %L2, %top

+  br i1 undef, label %L, label %L1

+

+L1:                                               ; preds = %L1.preheader, %L2

+  %r13 = phi i64 [ %r1, %L2 ], [ 1, %L ]

+; CHECK:  %lsr.iv = phi i64 [ 0, %L{{[^ ]+}} ], [ %lsr.iv.next, %L2 ]

+; CHECK-NOT:  %lsr.iv = phi i64 [ -1, %L{{[^ ]+}} ], [ %lsr.iv.next, %L2 ]

+; CHECK:  br

+  %r0 = add i64 %r13, -1

+  br label %idxend.8

+

+L2:                                               ; preds = %idxend.8

+  %r1 = add i64 %r13, 1

+  br i1 undef, label %L, label %L1

+

+if6:                                              ; preds = %idxend.8

+  %r2 = add i64 %0, -1

+  %r3 = load i64, i64* %1, align 8

+; CHECK-NOT:  %r2

+; CHECK:  %r3 = load i64

+  br label %ib

+

+idxend.8:                                         ; preds = %L1

+  br i1 undef, label %if6, label %L2

+

+ib:                                               ; preds = %if6

+  %r4 = mul i64 %r3, %r0

+  %r5 = add i64 %r2, %r4

+  %r6 = icmp ult i64 %r5, undef

+; CHECK  %2 = mul i64 %lsr.iv, %r3

+; CHECK  %3 = add i64 %1, -1

+; CHECK  %4 = add i64 %0, %r3

+; CHECK  %r6

+  %r7 = getelementptr i64, i64* undef, i64 %r5

+  store i64 1, i64* %r7, align 8

+; CHECK  %5 = mul i64 %lsr.iv, %r3

+; CHECK  %6 = add i64 %5, -1

+  br label %L

+}