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a0999051a2
This re-commits r265535 which was reverted in r265541 because it broke the windows bots. The problem was that we had a PointerIntPair which took a pointer to a struct allocated with new. The problem was that new doesn't provide sufficient alignment guarantees. This pattern was already present before r265535 and it just happened to work. To fix this, we now separate the PointerToIntPair from the ExitNotTakenInfo struct into a pointer and a bool. Original commit message: Summary: When the backedge taken codition is computed from an icmp, SCEV can deduce the backedge taken count only if one of the sides of the icmp is an AddRecExpr. However, due to sign/zero extensions, we sometimes end up with something that is not an AddRecExpr. However, we can use SCEV predicates to produce a 'guarded' expression. This change adds a method to SCEV to get this expression, and the SCEV predicate associated with it. In HowManyGreaterThans and HowManyLessThans we will now add a SCEV predicate associated with the guarded backedge taken count when the analyzed SCEV expression is not an AddRecExpr. Note that we only do this as an alternative to returning a 'CouldNotCompute'. We use new feature in Loop Access Analysis and LoopVectorize to analyze and transform more loops. Reviewers: anemet, mzolotukhin, hfinkel, sanjoy Subscribers: flyingforyou, mcrosier, atrick, mssimpso, sanjoy, mzolotukhin, llvm-commits Differential Revision: http://reviews.llvm.org/D17201 llvm-svn: 265786
110 lines
3.9 KiB
LLVM
110 lines
3.9 KiB
LLVM
; RUN: opt < %s -analyze -scalar-evolution | FileCheck %s
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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@A = weak global [1000 x i32] zeroinitializer, align 32
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; The resulting predicate is i16 {0,+,1} <nssw>, meanining
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; that the resulting backedge expression will be valid for:
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; (1 + (-1 smax %M)) <= MAX_INT16
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;
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; At the limit condition for M (MAX_INT16 - 1) we have in the
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; last iteration:
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; i0 <- MAX_INT16
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; i0.ext <- MAX_INT16
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;
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; and therefore no wrapping happend for i0 or i0.ext
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; throughout the execution of the loop. The resulting predicated
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; backedge taken count is correct.
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; CHECK: Classifying expressions for: @test1
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; CHECK: %i.0.ext = sext i16 %i.0 to i32
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; CHECK-NEXT: --> (sext i16 {0,+,1}<%bb3> to i32)
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; CHECK: Loop %bb3: Unpredictable backedge-taken count.
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; CHECK-NEXT: Loop %bb3: Unpredictable max backedge-taken count.
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; CHECK-NEXT: Loop %bb3: Predicated backedge-taken count is (1 + (-1 smax %M))
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; CHECK-NEXT: Predicates:
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; CHECK-NEXT: {0,+,1}<%bb3> Added Flags: <nssw>
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define void @test1(i32 %N, i32 %M) {
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entry:
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br label %bb3
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bb: ; preds = %bb3
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%tmp = getelementptr [1000 x i32], [1000 x i32]* @A, i32 0, i16 %i.0 ; <i32*> [#uses=1]
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store i32 123, i32* %tmp
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%tmp2 = add i16 %i.0, 1 ; <i32> [#uses=1]
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br label %bb3
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bb3: ; preds = %bb, %entry
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%i.0 = phi i16 [ 0, %entry ], [ %tmp2, %bb ] ; <i32> [#uses=3]
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%i.0.ext = sext i16 %i.0 to i32
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%tmp3 = icmp sle i32 %i.0.ext, %M ; <i1> [#uses=1]
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br i1 %tmp3, label %bb, label %bb5
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bb5: ; preds = %bb3
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br label %return
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return: ; preds = %bb5
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ret void
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}
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; The predicated backedge taken count is:
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; (2 + (zext i16 %Start to i32) + ((-2 + (-1 * (sext i16 %Start to i32)))
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; smax (-1 + (-1 * %M)))
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; )
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; -1 + (-1 * %M) <= (-2 + (-1 * (sext i16 %Start to i32))
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; The predicated backedge taken count is 0.
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; From the IR, this is correct since we will bail out at the
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; first iteration.
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; * -1 + (-1 * %M) > (-2 + (-1 * (sext i16 %Start to i32))
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; or: %M < 1 + (sext i16 %Start to i32)
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;
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; The predicated backedge taken count is 1 + (zext i16 %Start to i32) - %M
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;
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; If %M >= MIN_INT + 1, this predicated backedge taken count would be correct (even
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; without predicates). However, for %M < MIN_INT this would be an infinite loop.
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; In these cases, the {%Start,+,-1} <nusw> predicate would be false, as the
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; final value of the expression {%Start,+,-1} expression (%M - 1) would not be
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; representable as an i16.
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; There is also a limit case here where the value of %M is MIN_INT. In this case
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; we still have an infinite loop, since icmp sge %x, MIN_INT will always return
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; true.
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; CHECK: Classifying expressions for: @test2
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; CHECK: %i.0.ext = sext i16 %i.0 to i32
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; CHECK-NEXT: --> (sext i16 {%Start,+,-1}<%bb3> to i32)
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; CHECK: Loop %bb3: Unpredictable backedge-taken count.
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; CHECK-NEXT: Loop %bb3: Unpredictable max backedge-taken count.
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; CHECK-NEXT: Loop %bb3: Predicated backedge-taken count is (2 + (sext i16 %Start to i32) + ((-2 + (-1 * (sext i16 %Start to i32))) smax (-1 + (-1 * %M))))
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; CHECK-NEXT: Predicates:
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; CHECK-NEXT: {%Start,+,-1}<%bb3> Added Flags: <nssw>
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define void @test2(i32 %N, i32 %M, i16 %Start) {
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entry:
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br label %bb3
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bb: ; preds = %bb3
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%tmp = getelementptr [1000 x i32], [1000 x i32]* @A, i32 0, i16 %i.0 ; <i32*> [#uses=1]
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store i32 123, i32* %tmp
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%tmp2 = sub i16 %i.0, 1 ; <i32> [#uses=1]
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br label %bb3
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bb3: ; preds = %bb, %entry
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%i.0 = phi i16 [ %Start, %entry ], [ %tmp2, %bb ] ; <i32> [#uses=3]
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%i.0.ext = sext i16 %i.0 to i32
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%tmp3 = icmp sge i32 %i.0.ext, %M ; <i1> [#uses=1]
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br i1 %tmp3, label %bb, label %bb5
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bb5: ; preds = %bb3
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br label %return
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return: ; preds = %bb5
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ret void
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}
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