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llvm/test/CodeGen/SystemZ/branch-08.ll

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[SystemZ] Move compare-and-branch generation even later r187116 moved compare-and-branch generation from the instruction-selection pass to the peephole optimizer (via optimizeCompare). It turns out that even this is a bit too early. Fused compare-and-branch instructions don't interact well with predication, where a CC result is needed. They also make it harder to reuse the CC side-effects of earlier instructions (not yet implemented, but the subject of a later patch). Another problem was that the AnalyzeBranch family of routines weren't handling compares and branches, so we weren't able to reverse the fused form in cases where we would reverse a separate branch. This could have been fixed by extending AnalyzeBranch, but given the other problems, I've instead moved the fusing to the long-branch pass, which is also responsible for the opposite transformation: splitting out-of-range compares and branches into separate compares and long branches. I've added a test for the AnalyzeBranch problem. A test for the predication problem is included in the next patch, which fixes a bug in the choice of CC mask. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187494 91177308-0d34-0410-b5e6-96231b3b80d8
2013-07-31 12:11:07 +00:00
; Test SystemZInstrInfo::AnalyzeBranch and SystemZInstrInfo::InsertBranch.
;
; RUN: llc < %s -mtriple=s390x-linux-gnu | FileCheck %s
declare void @foo() noreturn
; Check a case where a separate branch is needed and where the original
; order should be reversed.
[SystemZ] Add unsigned compare-and-branch instructions For some reason I never got around to adding these at the same time as the signed versions. No idea why. I'm not sure whether this SystemZII::BranchC* stuff is useful, or whether it should just be replaced with an "is normal" flag. I'll leave that for later though. There are some boundary conditions that can be tweaked, such as preferring unsigned comparisons for equality with [128, 256), and "<= 255" over "< 256", but again I'll leave those for a separate patch. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190930 91177308-0d34-0410-b5e6-96231b3b80d8
2013-09-18 09:56:40 +00:00
define i32 @f1(i32 %a, i32 *%bptr) {
[SystemZ] Move compare-and-branch generation even later r187116 moved compare-and-branch generation from the instruction-selection pass to the peephole optimizer (via optimizeCompare). It turns out that even this is a bit too early. Fused compare-and-branch instructions don't interact well with predication, where a CC result is needed. They also make it harder to reuse the CC side-effects of earlier instructions (not yet implemented, but the subject of a later patch). Another problem was that the AnalyzeBranch family of routines weren't handling compares and branches, so we weren't able to reverse the fused form in cases where we would reverse a separate branch. This could have been fixed by extending AnalyzeBranch, but given the other problems, I've instead moved the fusing to the long-branch pass, which is also responsible for the opposite transformation: splitting out-of-range compares and branches into separate compares and long branches. I've added a test for the AnalyzeBranch problem. A test for the predication problem is included in the next patch, which fixes a bug in the choice of CC mask. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187494 91177308-0d34-0410-b5e6-96231b3b80d8
2013-07-31 12:11:07 +00:00
; CHECK-LABEL: f1:
[SystemZ] Add unsigned compare-and-branch instructions For some reason I never got around to adding these at the same time as the signed versions. No idea why. I'm not sure whether this SystemZII::BranchC* stuff is useful, or whether it should just be replaced with an "is normal" flag. I'll leave that for later though. There are some boundary conditions that can be tweaked, such as preferring unsigned comparisons for equality with [128, 256), and "<= 255" over "< 256", but again I'll leave those for a separate patch. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190930 91177308-0d34-0410-b5e6-96231b3b80d8
2013-09-18 09:56:40 +00:00
; CHECK: cl %r2, 0(%r3)
[SystemZ] Be more careful about inverting CC masks System z branches have a mask to select which of the 4 CC values should cause the branch to be taken. We can invert a branch by inverting the mask. However, not all instructions can produce all 4 CC values, so inverting the branch like this can lead to some oddities. For example, integer comparisons only produce a CC of 0 (equal), 1 (less) or 2 (greater). If an integer EQ is reversed to NE before instruction selection, the branch will test for 1 or 2. If instead the branch is reversed after instruction selection (by inverting the mask), it will test for 1, 2 or 3. Both are correct, but the second isn't really canonical. This patch therefore keeps track of which CC values are possible and uses this when inverting a mask. Although this is mostly cosmestic, it fixes undefined behavior for the CIJNLH in branch-08.ll. Another fix would have been to mask out bit 0 when generating the fused compare and branch, but the point of this patch is that we shouldn't need to do that in the first place. The patch also makes it easier to reuse CC results from other instructions. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187495 91177308-0d34-0410-b5e6-96231b3b80d8
2013-07-31 12:30:20 +00:00
; CHECK: jl .L[[LABEL:.*]]
[SystemZ] Move compare-and-branch generation even later r187116 moved compare-and-branch generation from the instruction-selection pass to the peephole optimizer (via optimizeCompare). It turns out that even this is a bit too early. Fused compare-and-branch instructions don't interact well with predication, where a CC result is needed. They also make it harder to reuse the CC side-effects of earlier instructions (not yet implemented, but the subject of a later patch). Another problem was that the AnalyzeBranch family of routines weren't handling compares and branches, so we weren't able to reverse the fused form in cases where we would reverse a separate branch. This could have been fixed by extending AnalyzeBranch, but given the other problems, I've instead moved the fusing to the long-branch pass, which is also responsible for the opposite transformation: splitting out-of-range compares and branches into separate compares and long branches. I've added a test for the AnalyzeBranch problem. A test for the predication problem is included in the next patch, which fixes a bug in the choice of CC mask. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187494 91177308-0d34-0410-b5e6-96231b3b80d8
2013-07-31 12:11:07 +00:00
; CHECK: br %r14
; CHECK: .L[[LABEL]]:
; CHECK: brasl %r14, foo@PLT
entry:
[SystemZ] Add unsigned compare-and-branch instructions For some reason I never got around to adding these at the same time as the signed versions. No idea why. I'm not sure whether this SystemZII::BranchC* stuff is useful, or whether it should just be replaced with an "is normal" flag. I'll leave that for later though. There are some boundary conditions that can be tweaked, such as preferring unsigned comparisons for equality with [128, 256), and "<= 255" over "< 256", but again I'll leave those for a separate patch. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190930 91177308-0d34-0410-b5e6-96231b3b80d8
2013-09-18 09:56:40 +00:00
%b = load i32 *%bptr
[SystemZ] Move compare-and-branch generation even later r187116 moved compare-and-branch generation from the instruction-selection pass to the peephole optimizer (via optimizeCompare). It turns out that even this is a bit too early. Fused compare-and-branch instructions don't interact well with predication, where a CC result is needed. They also make it harder to reuse the CC side-effects of earlier instructions (not yet implemented, but the subject of a later patch). Another problem was that the AnalyzeBranch family of routines weren't handling compares and branches, so we weren't able to reverse the fused form in cases where we would reverse a separate branch. This could have been fixed by extending AnalyzeBranch, but given the other problems, I've instead moved the fusing to the long-branch pass, which is also responsible for the opposite transformation: splitting out-of-range compares and branches into separate compares and long branches. I've added a test for the AnalyzeBranch problem. A test for the predication problem is included in the next patch, which fixes a bug in the choice of CC mask. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187494 91177308-0d34-0410-b5e6-96231b3b80d8
2013-07-31 12:11:07 +00:00
%cmp = icmp ult i32 %a, %b
br i1 %cmp, label %callit, label %return
callit:
call void @foo()
unreachable
return:
ret i32 1
}
; Same again with a fused compare and branch.
define i32 @f2(i32 %a) {
; CHECK-LABEL: f2:
[SystemZ] Be more careful about inverting CC masks System z branches have a mask to select which of the 4 CC values should cause the branch to be taken. We can invert a branch by inverting the mask. However, not all instructions can produce all 4 CC values, so inverting the branch like this can lead to some oddities. For example, integer comparisons only produce a CC of 0 (equal), 1 (less) or 2 (greater). If an integer EQ is reversed to NE before instruction selection, the branch will test for 1 or 2. If instead the branch is reversed after instruction selection (by inverting the mask), it will test for 1, 2 or 3. Both are correct, but the second isn't really canonical. This patch therefore keeps track of which CC values are possible and uses this when inverting a mask. Although this is mostly cosmestic, it fixes undefined behavior for the CIJNLH in branch-08.ll. Another fix would have been to mask out bit 0 when generating the fused compare and branch, but the point of this patch is that we shouldn't need to do that in the first place. The patch also makes it easier to reuse CC results from other instructions. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187495 91177308-0d34-0410-b5e6-96231b3b80d8
2013-07-31 12:30:20 +00:00
; CHECK: cije %r2, 0, .L[[LABEL:.*]]
[SystemZ] Move compare-and-branch generation even later r187116 moved compare-and-branch generation from the instruction-selection pass to the peephole optimizer (via optimizeCompare). It turns out that even this is a bit too early. Fused compare-and-branch instructions don't interact well with predication, where a CC result is needed. They also make it harder to reuse the CC side-effects of earlier instructions (not yet implemented, but the subject of a later patch). Another problem was that the AnalyzeBranch family of routines weren't handling compares and branches, so we weren't able to reverse the fused form in cases where we would reverse a separate branch. This could have been fixed by extending AnalyzeBranch, but given the other problems, I've instead moved the fusing to the long-branch pass, which is also responsible for the opposite transformation: splitting out-of-range compares and branches into separate compares and long branches. I've added a test for the AnalyzeBranch problem. A test for the predication problem is included in the next patch, which fixes a bug in the choice of CC mask. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187494 91177308-0d34-0410-b5e6-96231b3b80d8
2013-07-31 12:11:07 +00:00
; CHECK: br %r14
; CHECK: .L[[LABEL]]:
; CHECK: brasl %r14, foo@PLT
entry:
%cmp = icmp eq i32 %a, 0
br i1 %cmp, label %callit, label %return
callit:
call void @foo()
unreachable
return:
ret i32 1
}
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