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ba89ffcade
unswitching loops. Original patch trying to address this was sent in D47624, but that didn't quite handle things correctly. There are two key principles used to select whether and how to invalidate SCEV-cached information about loops: 1) We must invalidate any info SCEV has cached before unswitching as we may change (or destroy) the loop structure by the act of unswitching, and make it hard to recover everything we want to invalidate within SCEV. 2) We need to invalidate all of the loops whose CFGs are mutated by the unswitching. Notably, this isn't the *entire* loop nest, this is every loop contained by the outermost loop reached by an exit block relevant to the unswitch. And we need to do this even when doing trivial unswitching. I've added more focused tests that directly check that SCEV starts off with imprecise information and after unswitching (and simplifying instructions) re-querying SCEV will produce precise information. These tests also specifically work to check that an *outer* loop's information becomes precise. However, the testing here is still a bit imperfect. Crafting test cases that reliably fail to be analyzed by SCEV before unswitching and succeed afterward proved ... very, very hard. It took me several hours and careful work to build these, and I'm not optimistic about necessarily coming up with more to cover more elaborate possibilities. Fortunately, the code pattern we are testing here in the pass is really straightforward and reliable. Thanks to Max Kazantsev for the initial work on this as well as the review, and to Hal Finkel for helping me talk through approaches to test this stuff even if it didn't come to much. Differential Revision: https://reviews.llvm.org/D47624 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@336183 91177308-0d34-0410-b5e6-96231b3b80d8
189 lines
6.6 KiB
LLVM
189 lines
6.6 KiB
LLVM
; RUN: opt -passes='print<scalar-evolution>,loop(unswitch,loop-instsimplify),print<scalar-evolution>' -enable-nontrivial-unswitch -S < %s 2>%t.scev | FileCheck %s
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; RUN: FileCheck %s --check-prefix=SCEV < %t.scev
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target triple = "x86_64-unknown-linux-gnu"
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declare void @f()
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; Check that trivially unswitching an inner loop resets both the inner and outer
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; loop trip count.
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define void @test1(i32 %n, i32 %m, i1 %cond) {
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; Check that SCEV has no trip count before unswitching.
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; SCEV-LABEL: Determining loop execution counts for: @test1
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; SCEV: Loop %inner_loop_begin: <multiple exits> Unpredictable backedge-taken count.
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; SCEV: Loop %outer_loop_begin: Unpredictable backedge-taken count.
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;
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; Now check that after unswitching and simplifying instructions we get clean
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; backedge-taken counts.
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; SCEV-LABEL: Determining loop execution counts for: @test1
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; SCEV: Loop %inner_loop_begin: backedge-taken count is (-1 + (1 smax %m))<nsw>
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; SCEV: Loop %outer_loop_begin: backedge-taken count is (-1 + (1 smax %n))<nsw>
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;
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; And verify the code matches what we expect.
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; CHECK-LABEL: define void @test1(
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entry:
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br label %outer_loop_begin
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; Ensure the outer loop didn't get unswitched.
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; CHECK: entry:
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; CHECK-NEXT: br label %outer_loop_begin
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outer_loop_begin:
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%i = phi i32 [ %i.next, %outer_loop_latch ], [ 0, %entry ]
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; Block unswitching of the outer loop with a noduplicate call.
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call void @f() noduplicate
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br label %inner_loop_begin
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; Ensure the inner loop got unswitched into the outer loop.
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; CHECK: outer_loop_begin:
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; CHECK-NEXT: %{{.*}} = phi i32
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; CHECK-NEXT: call void @f()
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; CHECK-NEXT: br i1 %cond,
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inner_loop_begin:
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%j = phi i32 [ %j.next, %inner_loop_latch ], [ 0, %outer_loop_begin ]
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br i1 %cond, label %inner_loop_latch, label %inner_loop_early_exit
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inner_loop_latch:
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%j.next = add nsw i32 %j, 1
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%j.cmp = icmp slt i32 %j.next, %m
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br i1 %j.cmp, label %inner_loop_begin, label %inner_loop_late_exit
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inner_loop_early_exit:
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%j.lcssa = phi i32 [ %i, %inner_loop_begin ]
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br label %outer_loop_latch
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inner_loop_late_exit:
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br label %outer_loop_latch
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outer_loop_latch:
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%i.phi = phi i32 [ %j.lcssa, %inner_loop_early_exit ], [ %i, %inner_loop_late_exit ]
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%i.next = add nsw i32 %i.phi, 1
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%i.cmp = icmp slt i32 %i.next, %n
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br i1 %i.cmp, label %outer_loop_begin, label %exit
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exit:
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ret void
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}
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; Check that trivially unswitching an inner loop resets both the inner and outer
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; loop trip count.
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define void @test2(i32 %n, i32 %m, i32 %cond) {
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; Check that SCEV has no trip count before unswitching.
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; SCEV-LABEL: Determining loop execution counts for: @test2
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; SCEV: Loop %inner_loop_begin: <multiple exits> Unpredictable backedge-taken count.
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; SCEV: Loop %outer_loop_begin: Unpredictable backedge-taken count.
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;
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; Now check that after unswitching and simplifying instructions we get clean
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; backedge-taken counts.
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; SCEV-LABEL: Determining loop execution counts for: @test2
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; SCEV: Loop %inner_loop_begin: backedge-taken count is (-1 + (1 smax %m))<nsw>
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; FIXME: The following backedge taken count should be known but isn't apparently
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; just because of a switch in the outer loop.
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; SCEV: Loop %outer_loop_begin: Unpredictable backedge-taken count.
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;
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; CHECK-LABEL: define void @test2(
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entry:
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br label %outer_loop_begin
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; Ensure the outer loop didn't get unswitched.
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; CHECK: entry:
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; CHECK-NEXT: br label %outer_loop_begin
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outer_loop_begin:
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%i = phi i32 [ %i.next, %outer_loop_latch ], [ 0, %entry ]
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; Block unswitching of the outer loop with a noduplicate call.
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call void @f() noduplicate
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br label %inner_loop_begin
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; Ensure the inner loop got unswitched into the outer loop.
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; CHECK: outer_loop_begin:
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; CHECK-NEXT: %{{.*}} = phi i32
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; CHECK-NEXT: call void @f()
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; CHECK-NEXT: switch i32 %cond,
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inner_loop_begin:
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%j = phi i32 [ %j.next, %inner_loop_latch ], [ 0, %outer_loop_begin ]
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switch i32 %cond, label %inner_loop_early_exit [
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i32 1, label %inner_loop_latch
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i32 2, label %inner_loop_latch
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]
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inner_loop_latch:
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%j.next = add nsw i32 %j, 1
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%j.cmp = icmp slt i32 %j.next, %m
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br i1 %j.cmp, label %inner_loop_begin, label %inner_loop_late_exit
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inner_loop_early_exit:
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%j.lcssa = phi i32 [ %i, %inner_loop_begin ]
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br label %outer_loop_latch
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inner_loop_late_exit:
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br label %outer_loop_latch
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outer_loop_latch:
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%i.phi = phi i32 [ %j.lcssa, %inner_loop_early_exit ], [ %i, %inner_loop_late_exit ]
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%i.next = add nsw i32 %i.phi, 1
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%i.cmp = icmp slt i32 %i.next, %n
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br i1 %i.cmp, label %outer_loop_begin, label %exit
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exit:
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ret void
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}
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; Check that non-trivial unswitching of a branch in an inner loop into the outer
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; loop invalidates both inner and outer.
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define void @test3(i32 %n, i32 %m, i1 %cond) {
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; Check that SCEV has no trip count before unswitching.
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; SCEV-LABEL: Determining loop execution counts for: @test3
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; SCEV: Loop %inner_loop_begin: <multiple exits> Unpredictable backedge-taken count.
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; SCEV: Loop %outer_loop_begin: Unpredictable backedge-taken count.
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;
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; Now check that after unswitching and simplifying instructions we get clean
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; backedge-taken counts.
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; SCEV-LABEL: Determining loop execution counts for: @test3
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; SCEV: Loop %inner_loop_begin{{.*}}: backedge-taken count is (-1 + (1 smax %m))<nsw>
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; SCEV: Loop %outer_loop_begin: backedge-taken count is (-1 + (1 smax %n))<nsw>
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;
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; And verify the code matches what we expect.
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; CHECK-LABEL: define void @test3(
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entry:
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br label %outer_loop_begin
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; Ensure the outer loop didn't get unswitched.
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; CHECK: entry:
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; CHECK-NEXT: br label %outer_loop_begin
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outer_loop_begin:
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%i = phi i32 [ %i.next, %outer_loop_latch ], [ 0, %entry ]
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; Block unswitching of the outer loop with a noduplicate call.
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call void @f() noduplicate
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br label %inner_loop_begin
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; Ensure the inner loop got unswitched into the outer loop.
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; CHECK: outer_loop_begin:
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; CHECK-NEXT: %{{.*}} = phi i32
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; CHECK-NEXT: call void @f()
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; CHECK-NEXT: br i1 %cond,
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inner_loop_begin:
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%j = phi i32 [ %j.next, %inner_loop_latch ], [ 0, %outer_loop_begin ]
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%j.tmp = add nsw i32 %j, 1
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br i1 %cond, label %inner_loop_latch, label %inner_loop_early_exit
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inner_loop_latch:
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%j.next = add nsw i32 %j, 1
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%j.cmp = icmp slt i32 %j.next, %m
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br i1 %j.cmp, label %inner_loop_begin, label %inner_loop_late_exit
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inner_loop_early_exit:
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%j.lcssa = phi i32 [ %j.tmp, %inner_loop_begin ]
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br label %outer_loop_latch
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inner_loop_late_exit:
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br label %outer_loop_latch
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outer_loop_latch:
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%inc.phi = phi i32 [ %j.lcssa, %inner_loop_early_exit ], [ 1, %inner_loop_late_exit ]
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%i.next = add nsw i32 %i, %inc.phi
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%i.cmp = icmp slt i32 %i.next, %n
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br i1 %i.cmp, label %outer_loop_begin, label %exit
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exit:
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ret void
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}
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