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Eliminate switch cases that can never match, for example removes all

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negative switch cases if the branch condition is known to be positive.
Inspired by a recent improvement to GCC's VRP.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152405 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands
2012-03-09 13:45:18 +00:00
parent 7415659bf8
commit 6f1d799415
2 changed files with 186 additions and 1 deletions
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101
test/Transforms/CorrelatedValuePropagation/basic.ll
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@@ -79,4 +79,103 @@ Impossible:
LessThanOrEqualToTwo:
ret i32 0
}
}
define i32 @switch1(i32 %s) {
; CHECK: @switch1
entry:
%cmp = icmp slt i32 %s, 0
br i1 %cmp, label %negative, label %out
negative:
switch i32 %s, label %out [
; CHECK: switch i32 %s, label %out
i32 0, label %out
; CHECK-NOT: i32 0
i32 1, label %out
; CHECK-NOT: i32 1
i32 -1, label %next
; CHECK: i32 -1, label %next
i32 -2, label %next
; CHECK: i32 -2, label %next
i32 2, label %out
; CHECK-NOT: i32 2
i32 3, label %out
; CHECK-NOT: i32 3
]
out:
%p = phi i32 [ 1, %entry ], [ -1, %negative ], [ -1, %negative ], [ -1, %negative ], [ -1, %negative ]
ret i32 %p
next:
%q = phi i32 [ 0, %negative ], [ 0, %negative ]
ret i32 %q
}
define i32 @switch2(i32 %s) {
; CHECK: @switch2
entry:
%cmp = icmp sgt i32 %s, 0
br i1 %cmp, label %positive, label %out
positive:
switch i32 %s, label %out [
i32 0, label %out
i32 -1, label %next
i32 -2, label %next
]
; CHECK: br label %out
out:
%p = phi i32 [ -1, %entry ], [ 1, %positive ], [ 1, %positive ]
ret i32 %p
next:
%q = phi i32 [ 0, %positive ], [ 0, %positive ]
ret i32 %q
}
define i32 @switch3(i32 %s) {
; CHECK: @switch3
entry:
%cmp = icmp sgt i32 %s, 0
br i1 %cmp, label %positive, label %out
positive:
switch i32 %s, label %out [
i32 -1, label %out
i32 -2, label %next
i32 -3, label %next
]
; CHECK: br label %out
out:
%p = phi i32 [ -1, %entry ], [ 1, %positive ], [ 1, %positive ]
ret i32 %p
next:
%q = phi i32 [ 0, %positive ], [ 0, %positive ]
ret i32 %q
}
define void @switch4(i32 %s) {
; CHECK: @switch4
entry:
%cmp = icmp eq i32 %s, 0
br i1 %cmp, label %zero, label %out
zero:
switch i32 %s, label %out [
i32 0, label %next
i32 1, label %out
i32 -1, label %out
]
; CHECK: br label %next
out:
ret void
next:
ret void
}