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98ed51c042
The basic idea of the transform is to convert variant loop exit conditions into invariant exit conditions by changing the iteration on which the exit is taken when we know that the trip count is unobservable. See the original patch which introduced the code for a more complete explanation. The individual parts of this have been reviewed, the result has been fuzzed, and then further analyzed by hand, but despite all of that, I will not be suprised to see breakage here. If you see problems, please don't hesitate to revert - though please do provide a test case. The most likely class of issues are latent SCEV bugs and without a reduced test case, I'll be essentially stuck on reducing them. (Note: A bunch of tests were opted out of the new transform to preserve coverage. That landed in a previous commit to simplify revert cycles if they turn out to be needed.)
206 lines
5.7 KiB
LLVM
206 lines
5.7 KiB
LLVM
; RUN: opt < %s -S -indvars -loop-unroll -verify-loop-info | FileCheck %s
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;
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; Unit tests for loop unrolling using ScalarEvolution to compute trip counts.
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;
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; Indvars is run first to generate an "old" SCEV result. Some unit
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; tests may check that SCEV is properly invalidated between passes.
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; Completely unroll loops without a canonical IV.
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;
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; CHECK-LABEL: @sansCanonical(
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; CHECK-NOT: phi
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; CHECK-NOT: icmp
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; CHECK: ret
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define i32 @sansCanonical(i32* %base) nounwind {
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entry:
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br label %while.body
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while.body:
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%iv = phi i64 [ 10, %entry ], [ %iv.next, %while.body ]
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%sum = phi i32 [ 0, %entry ], [ %sum.next, %while.body ]
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%iv.next = add i64 %iv, -1
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%adr = getelementptr inbounds i32, i32* %base, i64 %iv.next
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%tmp = load i32, i32* %adr, align 8
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%sum.next = add i32 %sum, %tmp
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%iv.narrow = trunc i64 %iv.next to i32
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%cmp.i65 = icmp sgt i32 %iv.narrow, 0
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br i1 %cmp.i65, label %while.body, label %exit
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exit:
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ret i32 %sum
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}
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; SCEV unrolling properly handles loops with multiple exits. In this
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; case, the computed trip count based on a canonical IV is *not* for a
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; latch block. Canonical unrolling incorrectly unrolls it, but SCEV
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; unrolling does not.
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;
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; CHECK-LABEL: @earlyLoopTest(
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; CHECK: tail:
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; CHECK-NOT: br
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; CHECK: br i1 %cmp2, label %loop, label %exit2
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define i64 @earlyLoopTest(i64* %base) nounwind {
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entry:
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br label %loop
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loop:
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%iv = phi i64 [ 0, %entry ], [ %inc, %tail ]
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%s = phi i64 [ 0, %entry ], [ %s.next, %tail ]
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%adr = getelementptr i64, i64* %base, i64 %iv
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%val = load i64, i64* %adr
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%s.next = add i64 %s, %val
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%inc = add i64 %iv, 1
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%cmp = icmp ne i64 %inc, 4
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br i1 %cmp, label %tail, label %exit1
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tail:
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%cmp2 = icmp ne i64 %val, 0
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br i1 %cmp2, label %loop, label %exit2
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exit1:
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ret i64 %s
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exit2:
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ret i64 %s.next
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}
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; SCEV properly unrolls multi-exit loops.
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;
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; CHECK-LABEL: @multiExit(
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; CHECK: getelementptr i32, i32* %base, i32 %iv
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; CHECK-NEXT: load i32, i32*
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; CHECK: br i1 false, label %l2, label %exit1
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; CHECK: br i1 true, label %l1, label %exit2
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define i32 @multiExit(i32* %base) nounwind {
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entry:
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br label %l1
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l1:
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%iv1 = phi i32 [ 0, %entry ], [ %inc1, %l2 ]
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%iv2 = phi i32 [ 0, %entry ], [ %inc2, %l2 ]
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%inc1 = add i32 %iv1, 1
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%inc2 = add i32 %iv2, 1
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%adr = getelementptr i32, i32* %base, i32 %iv1
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%val = load i32, i32* %adr
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%cmp1 = icmp slt i32 %iv1, 5
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br i1 %cmp1, label %l2, label %exit1
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l2:
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%cmp2 = icmp slt i32 %iv2, 10
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br i1 %cmp2, label %l1, label %exit2
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exit1:
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ret i32 1
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exit2:
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ret i32 %val
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}
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; SCEV should not unroll a multi-exit loops unless the latch block has
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; a known trip count, regardless of the early exit trip counts. The
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; LoopUnroll utility uses this assumption to optimize the latch
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; block's branch.
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;
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; CHECK-LABEL: @multiExitIncomplete(
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; CHECK: l3:
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; CHECK-NOT: br
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; CHECK: br i1 %cmp3, label %l1, label %exit3
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define i32 @multiExitIncomplete(i32* %base) nounwind {
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entry:
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br label %l1
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l1:
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%iv1 = phi i32 [ 0, %entry ], [ %inc1, %l3 ]
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%iv2 = phi i32 [ 0, %entry ], [ %inc2, %l3 ]
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%inc1 = add i32 %iv1, 1
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%inc2 = add i32 %iv2, 1
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%adr = getelementptr i32, i32* %base, i32 %iv1
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%val = load i32, i32* %adr
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%cmp1 = icmp slt i32 %iv1, 5
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br i1 %cmp1, label %l2, label %exit1
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l2:
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%cmp2 = icmp slt i32 %iv2, 10
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br i1 %cmp2, label %l3, label %exit2
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l3:
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%cmp3 = icmp ne i32 %val, 0
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br i1 %cmp3, label %l1, label %exit3
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exit1:
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ret i32 1
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exit2:
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ret i32 2
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exit3:
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ret i32 3
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}
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; When loop unroll merges a loop exit with one of its parent loop's
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; exits, SCEV must forget its ExitNotTaken info.
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;
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; CHECK-LABEL: @nestedUnroll(
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; CHECK-NOT: br i1
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; CHECK: for.body87:
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define void @nestedUnroll() nounwind {
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entry:
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br label %for.inc
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for.inc:
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br i1 false, label %for.inc, label %for.body38.preheader
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for.body38.preheader:
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br label %for.body38
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for.body38:
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%i.113 = phi i32 [ %inc76, %for.inc74 ], [ 0, %for.body38.preheader ]
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%mul48 = mul nsw i32 %i.113, 6
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br label %for.body43
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for.body43:
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%j.011 = phi i32 [ 0, %for.body38 ], [ %inc72, %for.body43 ]
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%add49 = add nsw i32 %j.011, %mul48
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%sh_prom50 = zext i32 %add49 to i64
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%inc72 = add nsw i32 %j.011, 1
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br i1 false, label %for.body43, label %for.inc74
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for.inc74:
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%inc76 = add nsw i32 %i.113, 1
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br i1 false, label %for.body38, label %for.body87.preheader
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for.body87.preheader:
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br label %for.body87
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for.body87:
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br label %for.body87
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}
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; PR16130: clang produces incorrect code with loop/expression at -O2
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; rdar:14036816 loop-unroll makes assumptions about undefined behavior
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;
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; The loop latch is assumed to exit after the first iteration because
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; of the induction variable's NSW flag. However, the loop latch's
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; equality test is skipped and the loop exits after the second
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; iteration via the early exit. So loop unrolling cannot assume that
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; the loop latch's exit count of zero is an upper bound on the number
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; of iterations.
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;
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; CHECK-LABEL: @nsw_latch(
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; CHECK: for.body:
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; CHECK: %b.03 = phi i32 [ 0, %entry ], [ %add, %for.cond ]
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; CHECK: return:
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; CHECK: %b.03.lcssa = phi i32 [ 8, %for.body ], [ 0, %for.cond ]
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define void @nsw_latch(i32* %a) nounwind {
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entry:
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br label %for.body
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for.body: ; preds = %for.cond, %entry
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%b.03 = phi i32 [ 0, %entry ], [ %add, %for.cond ]
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%tobool = icmp eq i32 %b.03, 0
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%add = add nsw i32 %b.03, 8
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br i1 %tobool, label %for.cond, label %return
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for.cond: ; preds = %for.body
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%cmp = icmp eq i32 %add, 13
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br i1 %cmp, label %return, label %for.body
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return: ; preds = %for.body, %for.cond
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%b.03.lcssa = phi i32 [ %b.03, %for.body ], [ %b.03, %for.cond ]
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%retval.0 = phi i32 [ 1, %for.body ], [ 0, %for.cond ]
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store i32 %b.03.lcssa, i32* %a, align 4
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ret void
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}
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