6c99e63120
I think currently isImpliedViaMerge can incorrectly return true for phis in a loop/cycle, if the found condition involves the previous value of Consider the case in exit_cond_depends_on_inner_loop. At some point, we call (modulo simplifications) isImpliedViaMerge(<=, %x.lcssa, -1, %call, -1). The existing code tries to prove IncV <= -1 for all incoming values InvV using the found condition (%call <= -1). At the moment this succeeds, but only because it does not compare the same runtime value. The found condition checks the value of the last iteration, but the incoming value is from the *previous* iteration. Hence we incorrectly determine that the *previous* value was <= -1, which may not be true. I think we need to be more careful when looking at the incoming values here. In particular, we need to rule out that a found condition refers to any value that may refer to one of the previous iterations. I'm not sure there's a reliable way to do so (that also works of irreducible control flow). So for now this patch adds an additional requirement that the incoming value must properly dominate the phi block. This should ensure the values do not change in a cycle. I am not entirely sure if will catch all cases and I appreciate a through second look in that regard. Alternatively we could also unconditionally bail out in this case, instead of checking the incoming values Reviewed By: nikic Differential Revision: https://reviews.llvm.org/D101829
263 lines
7.3 KiB
LLVM
263 lines
7.3 KiB
LLVM
; RUN: opt -verify-loop-info -irce -S < %s | FileCheck %s
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; RUN: opt -verify-loop-info -passes='require<branch-prob>,irce' -S < %s | FileCheck %s
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define void @decrementing_loop(i32 *%arr, i32 *%a_len_ptr, i32 %n) {
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entry:
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%len = load i32, i32* %a_len_ptr, !range !0
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%first.itr.check = icmp sgt i32 %n, 0
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%start = sub i32 %n, 1
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br i1 %first.itr.check, label %loop, label %exit
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loop:
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%idx = phi i32 [ %start, %entry ] , [ %idx.dec, %in.bounds ]
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%idx.dec = sub i32 %idx, 1
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%abc.high = icmp slt i32 %idx, %len
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%abc.low = icmp sge i32 %idx, 0
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%abc = and i1 %abc.low, %abc.high
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br i1 %abc, label %in.bounds, label %out.of.bounds, !prof !1
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in.bounds:
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%addr = getelementptr i32, i32* %arr, i32 %idx
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store i32 0, i32* %addr
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%next = icmp sgt i32 %idx.dec, -1
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br i1 %next, label %loop, label %exit
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out.of.bounds:
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ret void
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exit:
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ret void
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; CHECK: loop.preheader:
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; CHECK: [[len_hiclamp:[^ ]+]] = call i32 @llvm.smin.i32(i32 %len, i32 %n)
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; CHECK: [[not_exit_preloop_at:[^ ]+]] = call i32 @llvm.smax.i32(i32 [[len_hiclamp]], i32 0)
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; CHECK: %exit.preloop.at = add nsw i32 [[not_exit_preloop_at]], -1
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}
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; Make sure that we can eliminate the range check when the loop looks like:
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; for (i = len.a - 1; i >= 0; --i)
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; b[i] = a[i];
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define void @test_01(i32* %a, i32* %b, i32* %a_len_ptr, i32* %b_len_ptr) {
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; CHECK-LABEL: test_01
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; CHECK: mainloop:
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; CHECK-NEXT: br label %loop
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; CHECK: loop:
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; CHECK: %rc = and i1 true, true
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; CHECK: loop.preloop:
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entry:
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%len.a = load i32, i32* %a_len_ptr, !range !0
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%len.b = load i32, i32* %b_len_ptr, !range !0
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%first.itr.check = icmp ne i32 %len.a, 0
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br i1 %first.itr.check, label %loop, label %exit
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loop:
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%idx = phi i32 [ %len.a, %entry ] , [ %idx.next, %in.bounds ]
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%idx.next = sub i32 %idx, 1
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%rca = icmp ult i32 %idx.next, %len.a
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%rcb = icmp ult i32 %idx.next, %len.b
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%rc = and i1 %rca, %rcb
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br i1 %rc, label %in.bounds, label %out.of.bounds, !prof !1
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in.bounds:
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%el.a = getelementptr i32, i32* %a, i32 %idx.next
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%el.b = getelementptr i32, i32* %b, i32 %idx.next
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%v = load i32, i32* %el.a
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store i32 %v, i32* %el.b
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%loop.cond = icmp slt i32 %idx, 2
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br i1 %loop.cond, label %exit, label %loop
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out.of.bounds:
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ret void
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exit:
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ret void
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}
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; Same as test_01, but the latch condition is unsigned
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define void @test_02(i32* %a, i32* %b, i32* %a_len_ptr, i32* %b_len_ptr) {
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; CHECK-LABEL: test_02
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; CHECK: mainloop:
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; CHECK-NEXT: br label %loop
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; CHECK: loop:
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; CHECK: %rc = and i1 true, true
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; CHECK: loop.preloop:
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entry:
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%len.a = load i32, i32* %a_len_ptr, !range !0
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%len.b = load i32, i32* %b_len_ptr, !range !0
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%first.itr.check = icmp ne i32 %len.a, 0
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br i1 %first.itr.check, label %loop, label %exit
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loop:
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%idx = phi i32 [ %len.a, %entry ] , [ %idx.next, %in.bounds ]
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%idx.next = sub i32 %idx, 1
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%rca = icmp ult i32 %idx.next, %len.a
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%rcb = icmp ult i32 %idx.next, %len.b
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%rc = and i1 %rca, %rcb
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br i1 %rc, label %in.bounds, label %out.of.bounds, !prof !1
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in.bounds:
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%el.a = getelementptr i32, i32* %a, i32 %idx.next
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%el.b = getelementptr i32, i32* %b, i32 %idx.next
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%v = load i32, i32* %el.a
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store i32 %v, i32* %el.b
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%loop.cond = icmp ult i32 %idx, 2
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br i1 %loop.cond, label %exit, label %loop
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out.of.bounds:
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ret void
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exit:
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ret void
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}
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; Check that we can figure out that IV is non-negative via implication through
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; Phi node.
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define void @test_03(i32* %a, i32* %a_len_ptr, i1 %cond) {
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; CHECK-LABEL: test_03
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; CHECK: mainloop:
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; CHECK-NEXT: br label %loop
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; CHECK: loop:
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; CHECK: br i1 true, label %in.bounds, label %out.of.bounds
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; CHECK: loop.preloop:
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entry:
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%len.a = load i32, i32* %a_len_ptr, !range !0
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%len.minus.one = sub nsw i32 %len.a, 1
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%len.minus.two = sub nsw i32 %len.a, 2
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br i1 %cond, label %if.true, label %if.false
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if.true:
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br label %merge
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if.false:
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br label %merge
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merge:
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%starting.value = phi i32 [ %len.minus.two, %if.true ], [ %len.minus.one, %if.false ]
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%first.itr.check = icmp sgt i32 %len.a, 3
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br i1 %first.itr.check, label %loop, label %exit
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loop:
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%idx = phi i32 [ %starting.value, %merge ] , [ %idx.next, %in.bounds ]
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%idx.next = sub i32 %idx, 1
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%rc = icmp ult i32 %idx.next, %len.a
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br i1 %rc, label %in.bounds, label %out.of.bounds, !prof !1
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in.bounds:
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%el.a = getelementptr i32, i32* %a, i32 %idx.next
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%v = load i32, i32* %el.a
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%loop.cond = icmp slt i32 %idx, 2
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br i1 %loop.cond, label %exit, label %loop
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out.of.bounds:
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ret void
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exit:
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ret void
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}
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; Check that we can figure out that IV is non-negative via implication through
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; two Phi nodes.
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define void @test_04(i32* %a, i32* %a_len_ptr, i1 %cond) {
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; CHECK-LABEL: test_04
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; CHECK: mainloop:
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; CHECK-NEXT: br label %loop
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; CHECK: loop:
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; CHECK: br i1 true, label %in.bounds, label %out.of.bounds
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; CHECK: loop.preloop:
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entry:
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%len.a = load i32, i32* %a_len_ptr, !range !0
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%len.minus.one = sub nsw i32 %len.a, 1
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%len.plus.one = add nsw i32 %len.a, 1
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%len.minus.two = sub nsw i32 %len.a, 2
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br i1 %cond, label %if.true, label %if.false
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if.true:
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br label %merge
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if.false:
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br label %merge
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merge:
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%starting.value = phi i32 [ %len.minus.two, %if.true ], [ %len.minus.one, %if.false ]
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%len.phi = phi i32 [ %len.a, %if.true ], [ %len.plus.one, %if.false ]
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%first.itr.check = icmp sgt i32 %len.a, 3
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br i1 %first.itr.check, label %loop, label %exit
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loop:
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%idx = phi i32 [ %starting.value, %merge ] , [ %idx.next, %in.bounds ]
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%idx.next = sub i32 %idx, 1
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%rc = icmp ult i32 %idx.next, %len.phi
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br i1 %rc, label %in.bounds, label %out.of.bounds, !prof !1
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in.bounds:
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%el.a = getelementptr i32, i32* %a, i32 %idx.next
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%v = load i32, i32* %el.a
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%loop.cond = icmp slt i32 %idx, 2
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br i1 %loop.cond, label %exit, label %loop
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out.of.bounds:
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ret void
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exit:
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ret void
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}
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; TODO: we need to be more careful when trying to look through phi nodes in
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; cycles, because the condition to prove may reference the previous value of
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; the phi. So we currently fail to optimize this case.
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; Check that we can figure out that IV is non-negative via implication through
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; two Phi nodes, one being AddRec.
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define void @test_05(i32* %a, i32* %a_len_ptr, i1 %cond) {
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; CHECK-LABEL: test_05
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; CHECK: entry:
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; CHECK: br label %merge
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; CHECK-NOT: mainloop
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entry:
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%len.a = load i32, i32* %a_len_ptr, !range !0
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%len.minus.one = sub nsw i32 %len.a, 1
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%len.plus.one = add nsw i32 %len.a, 1
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%len.minus.two = sub nsw i32 %len.a, 2
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br label %merge
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merge:
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%starting.value = phi i32 [ %len.minus.two, %entry ], [ %len.minus.one, %merge ]
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%len.phi = phi i32 [ %len.a, %entry ], [ %len.phi.next, %merge ]
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%len.phi.next = add nsw i32 %len.phi, 1
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br i1 true, label %first.iter.check, label %merge
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first.iter.check:
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%first.itr.check = icmp sgt i32 %len.a, 3
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br i1 %first.itr.check, label %loop, label %exit
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loop:
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%idx = phi i32 [ %starting.value, %first.iter.check ] , [ %idx.next, %in.bounds ]
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%idx.next = sub i32 %idx, 1
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%rc = icmp ult i32 %idx.next, %len.phi
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br i1 %rc, label %in.bounds, label %out.of.bounds, !prof !1
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in.bounds:
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%el.a = getelementptr i32, i32* %a, i32 %idx.next
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%v = load i32, i32* %el.a
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%loop.cond = icmp slt i32 %idx, 2
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br i1 %loop.cond, label %exit, label %loop
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out.of.bounds:
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ret void
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exit:
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ret void
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}
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!0 = !{i32 0, i32 2147483647}
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!1 = !{!"branch_weights", i32 64, i32 4}
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