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[SCEV] Strengthen variance condition in calculateLoopDisposition

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Given loops `L1` and `L2` with AddRecs `AR1` and `AR2` varying in them respectively.
When identifying loop disposition of `AR2` w.r.t. `L1`, we only say that it is varying if
`L1` contains `L2`. But there is also a possible situation where `L1` and `L2` are
consecutive sibling loops within the parent loop. In this case, `AR2` is also varying
w.r.t. `L1`, but we don't correctly identify it.

It can lead, for exaple, to attempt of incorrect folding. Consider:
  AR1 = {a,+,b}<L1>
  AR2 = {c,+,d}<L2>
  EXAR2 = sext(AR1)
  MUL = mul AR1, EXAR2
If we incorrectly assume that `EXAR2` is invariant w.r.t. `L1`, we can end up trying to
construct something like: `{a * {c,+,d}<L2>,+,b * {c,+,d}<L2>}<L1>`, which is incorrect
because `AR2` is not available on entrance of `L1`.

Both situations "`L1` contains `L2`" and "`L1` preceeds sibling loop `L2`" can be handled
with one check: "header of `L1` dominates header of `L2`". This patch replaces the old
insufficient check with this one.

Differential Revision: https://reviews.llvm.org/D39453


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@318819 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Max Kazantsev 2017-11-22 06:21:39 +00:00
parent 882fbe3d4c
commit f66b47b328
2 changed files with 123 additions and 2 deletions
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6
lib/Analysis/ScalarEvolution.cpp
View File

@ -10927,9 +10927,11 @@ ScalarEvolution::computeLoopDisposition(const SCEV *S, const Loop *L) {
if (!L)
return LoopVariant;
// This recurrence is variant w.r.t. L if L contains AR's loop.
if (L->contains(AR->getLoop()))
// Everything that is not defined at loop entry is variant.
if (DT.dominates(L->getHeader(), AR->getLoop()->getHeader()))
return LoopVariant;
assert(!L->contains(AR->getLoop()) && "Containing loop's header does not"
" dominate the contained loop's header?");
// This recurrence is invariant w.r.t. L if AR's loop contains L.
if (AR->getLoop()->contains(L))

119
test/Analysis/ScalarEvolution/different-loops-recs.ll
View File

@ -510,3 +510,122 @@ exit:
%tmp10 = add i32 %iv.1.2, 3
ret void
}
define i64 @test_09(i32 %param) {
; CHECK-LABEL: Classifying expressions for: @test_09
; CHECK: %iv1 = phi i64 [ %iv1.next, %guarded ], [ 0, %outer.loop ]
; CHECK-NEXT: --> {0,+,1}<nuw><nsw><%loop1>
; CHECK: %iv1.trunc = trunc i64 %iv1 to i32
; CHECK-NEXT: --> {0,+,1}<%loop1>
; CHECK: %iv1.next = add nuw nsw i64 %iv1, 1
; CHECK-NEXT: --> {1,+,1}<nuw><nsw><%loop1>
; CHECK: %iv2 = phi i32 [ %iv2.next, %loop2 ], [ %param, %loop2.preheader ]
; CHECK-NEXT: --> {%param,+,1}<%loop2>
; CHECK: %iv2.next = add i32 %iv2, 1
; CHECK-NEXT: --> {(1 + %param),+,1}<%loop2>
; CHECK: %iv2.ext = sext i32 %iv2.next to i64
; CHECK-NEXT: --> (sext i32 {(1 + %param),+,1}<%loop2> to i64)
; CHECK: %ret = mul i64 %iv1, %iv2.ext
; CHECK-NEXT: --> ((sext i32 {(1 + %param),+,1}<%loop2> to i64) * {0,+,1}<nuw><nsw><%loop1>)
entry:
br label %outer.loop
outer.loop: ; preds = %loop2.exit, %entry
br label %loop1
loop1: ; preds = %guarded, %outer.loop
%iv1 = phi i64 [ %iv1.next, %guarded ], [ 0, %outer.loop ]
%iv1.trunc = trunc i64 %iv1 to i32
%cond1 = icmp ult i64 %iv1, 100
br i1 %cond1, label %guarded, label %deopt
guarded: ; preds = %loop1
%iv1.next = add nuw nsw i64 %iv1, 1
%tmp16 = icmp slt i32 %iv1.trunc, 2
br i1 %tmp16, label %loop1, label %loop2.preheader
deopt: ; preds = %loop1
unreachable
loop2.preheader: ; preds = %guarded
br label %loop2
loop2: ; preds = %loop2, %loop2.preheader
%iv2 = phi i32 [ %iv2.next, %loop2 ], [ %param, %loop2.preheader ]
%iv2.next = add i32 %iv2, 1
%cond2 = icmp slt i32 %iv2, %iv1.trunc
br i1 %cond2, label %loop2, label %exit
exit: ; preds = %loop2.exit
%iv2.ext = sext i32 %iv2.next to i64
%ret = mul i64 %iv1, %iv2.ext
ret i64 %ret
}
define i64 @test_10(i32 %param) {
; CHECK-LABEL: Classifying expressions for: @test_10
; CHECK: %uncle = phi i64 [ %uncle.outer.next, %uncle.loop.backedge ], [ 0, %outer.loop ]
; CHECK-NEXT: --> {0,+,1}<%uncle.loop>
; CHECK: %iv1 = phi i64 [ %iv1.next, %guarded ], [ 0, %uncle.loop ]
; CHECK-NEXT: --> {0,+,1}<nuw><nsw><%loop1>
; CHECK: %iv1.trunc = trunc i64 %iv1 to i32
; CHECK-NEXT: --> {0,+,1}<%loop1>
; CHECK: %iv1.next = add nuw nsw i64 %iv1, 1
; CHECK-NEXT: --> {1,+,1}<nuw><nsw><%loop1>
; CHECK: %uncle.outer.next = add i64 %uncle, 1
; CHECK-NEXT: --> {1,+,1}<%uncle.loop>
; CHECK: %iv2 = phi i32 [ %iv2.next, %loop2 ], [ %param, %loop2.preheader ]
; CHECK-NEXT: --> {%param,+,1}<%loop2>
; CHECK: %iv2.next = add i32 %iv2, 1
; CHECK-NEXT: --> {(1 + %param),+,1}<%loop2>
; CHECK: %iv2.ext = sext i32 %iv2.next to i64
; CHECK-NEXT: --> (sext i32 {(1 + %param),+,1}<%loop2> to i64)
; CHECK: %ret = mul i64 %iv1, %iv2.ext
; CHECK-NEXT: --> ((sext i32 {(1 + %param),+,1}<%loop2> to i64) * {0,+,1}<nuw><nsw><%loop1>)
entry:
br label %outer.loop
outer.loop: ; preds = %entry
br label %uncle.loop
uncle.loop: ; preds = %uncle.loop.backedge, %outer.loop
%uncle = phi i64 [ %uncle.outer.next, %uncle.loop.backedge ], [ 0, %outer.loop ]
br label %loop1
loop1: ; preds = %guarded, %uncle.loop
%iv1 = phi i64 [ %iv1.next, %guarded ], [ 0, %uncle.loop ]
%iv1.trunc = trunc i64 %iv1 to i32
%cond1 = icmp ult i64 %iv1, 100
br i1 %cond1, label %guarded, label %deopt
guarded: ; preds = %loop1
%iv1.next = add nuw nsw i64 %iv1, 1
%tmp16 = icmp slt i32 %iv1.trunc, 2
br i1 %tmp16, label %loop1, label %uncle.loop.backedge
uncle.loop.backedge: ; preds = %guarded
%uncle.outer.next = add i64 %uncle, 1
%cond.uncle = icmp ult i64 %uncle, 120
br i1 %cond.uncle, label %loop2.preheader, label %uncle.loop
deopt: ; preds = %loop1
unreachable
loop2.preheader: ; preds = %uncle.loop.backedge
br label %loop2
loop2: ; preds = %loop2, %loop2.preheader
%iv2 = phi i32 [ %iv2.next, %loop2 ], [ %param, %loop2.preheader ]
%iv2.next = add i32 %iv2, 1
%cond2 = icmp slt i32 %iv2, %iv1.trunc
br i1 %cond2, label %loop2, label %exit
exit: ; preds = %loop2
%iv2.ext = sext i32 %iv2.next to i64
%ret = mul i64 %iv1, %iv2.ext
ret i64 %ret
}