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reinstate r222872: Peephole optimization in switch table lookup: reuse the guarding table comparison if possible.

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Fixed missing dominance check.
Original commit message:

This optimization tries to reuse the generated compare instruction, if there is a comparison against the default value after the switch.
Example:
   if (idx < tablesize)
      r = table[idx]; // table does not contain default_value
   else
      r = default_value;
   if (r != default_value)
      ...
Is optimized to:
   cond = idx < tablesize;
   if (cond)
      r = table[idx];
   else
      r = default_value;
   if (cond)
      ...
Jump threading will then eliminate the second if(cond).



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222891 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Erik Eckstein
2014-11-27 15:13:14 +00:00
parent c0b24f7949
commit 6cfbf12d77
2 changed files with 227 additions and 7 deletions
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127
test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
View File

@@ -1077,3 +1077,130 @@ return:
; CHECK-NEXT: ret i8 %switch.idx.cast
}
; Reuse the inverted table range compare.
define i32 @reuse_cmp1(i32 %x) {
entry:
switch i32 %x, label %sw.default [
i32 0, label %sw.bb
i32 1, label %sw.bb1
i32 2, label %sw.bb2
i32 3, label %sw.bb3
]
sw.bb: br label %sw.epilog
sw.bb1: br label %sw.epilog
sw.bb2: br label %sw.epilog
sw.bb3: br label %sw.epilog
sw.default: br label %sw.epilog
sw.epilog:
%r.0 = phi i32 [ 0, %sw.default ], [ 13, %sw.bb3 ], [ 12, %sw.bb2 ], [ 11, %sw.bb1 ], [ 10, %sw.bb ]
%cmp = icmp eq i32 %r.0, 0 ; This compare can be "replaced".
br i1 %cmp, label %if.then, label %if.end
if.then: br label %return
if.end: br label %return
return:
%retval.0 = phi i32 [ 100, %if.then ], [ %r.0, %if.end ]
ret i32 %retval.0
; CHECK-LABEL: @reuse_cmp1(
; CHECK: entry:
; CHECK-NEXT: %switch.tableidx = sub i32 %x, 0
; CHECK-NEXT: [[C:%.+]] = icmp ult i32 %switch.tableidx, 4
; CHECK-NEXT: %inverted.cmp = xor i1 [[C]], true
; CHECK: [[R:%.+]] = select i1 %inverted.cmp, i32 100, i32 {{.*}}
; CHECK-NEXT: ret i32 [[R]]
}
; Reuse the table range compare.
define i32 @reuse_cmp2(i32 %x) {
entry:
switch i32 %x, label %sw.default [
i32 0, label %sw.bb
i32 1, label %sw.bb1
i32 2, label %sw.bb2
i32 3, label %sw.bb3
]
sw.bb: br label %sw.epilog
sw.bb1: br label %sw.epilog
sw.bb2: br label %sw.epilog
sw.bb3: br label %sw.epilog
sw.default: br label %sw.epilog
sw.epilog:
%r.0 = phi i32 [ 4, %sw.default ], [ 3, %sw.bb3 ], [ 2, %sw.bb2 ], [ 1, %sw.bb1 ], [ 0, %sw.bb ]
%cmp = icmp ne i32 %r.0, 4 ; This compare can be "replaced".
br i1 %cmp, label %if.then, label %if.end
if.then: br label %return
if.end: br label %return
return:
%retval.0 = phi i32 [ %r.0, %if.then ], [ 100, %if.end ]
ret i32 %retval.0
; CHECK-LABEL: @reuse_cmp2(
; CHECK: entry:
; CHECK-NEXT: %switch.tableidx = sub i32 %x, 0
; CHECK-NEXT: [[C:%.+]] = icmp ult i32 %switch.tableidx, 4
; CHECK: [[R:%.+]] = select i1 [[C]], i32 {{.*}}, i32 100
; CHECK-NEXT: ret i32 [[R]]
}
; Cannot reuse the table range compare, because the default value is the same
; as one of the case values.
define i32 @no_reuse_cmp(i32 %x) {
entry:
switch i32 %x, label %sw.default [
i32 0, label %sw.bb
i32 1, label %sw.bb1
i32 2, label %sw.bb2
i32 3, label %sw.bb3
]
sw.bb: br label %sw.epilog
sw.bb1: br label %sw.epilog
sw.bb2: br label %sw.epilog
sw.bb3: br label %sw.epilog
sw.default: br label %sw.epilog
sw.epilog:
%r.0 = phi i32 [ 12, %sw.default ], [ 13, %sw.bb3 ], [ 12, %sw.bb2 ], [ 11, %sw.bb1 ], [ 10, %sw.bb ]
%cmp = icmp ne i32 %r.0, 0
br i1 %cmp, label %if.then, label %if.end
if.then: br label %return
if.end: br label %return
return:
%retval.0 = phi i32 [ %r.0, %if.then ], [ 100, %if.end ]
ret i32 %retval.0
; CHECK-LABEL: @no_reuse_cmp(
; CHECK: [[S:%.+]] = select
; CHECK-NEXT: %cmp = icmp ne i32 [[S]], 0
; CHECK-NEXT: [[R:%.+]] = select i1 %cmp, i32 [[S]], i32 100
; CHECK-NEXT: ret i32 [[R]]
}
; Cannot reuse the table range compare, because the phi at the switch merge
; point is not dominated by the switch.
define i32 @no_reuse_cmp2(i32 %x, i32 %y) {
entry:
%ec = icmp ne i32 %y, 0
br i1 %ec, label %switch.entry, label %sw.epilog
switch.entry:
switch i32 %x, label %sw.default [
i32 0, label %sw.bb
i32 1, label %sw.bb1
i32 2, label %sw.bb2
i32 3, label %sw.bb3
]
sw.bb: br label %sw.epilog
sw.bb1: br label %sw.epilog
sw.bb2: br label %sw.epilog
sw.bb3: br label %sw.epilog
sw.default: br label %sw.epilog
sw.epilog:
%r.0 = phi i32 [100, %entry], [ 0, %sw.default ], [ 13, %sw.bb3 ], [ 12, %sw.bb2 ], [ 11, %sw.bb1 ], [ 10, %sw.bb ]
%cmp = icmp eq i32 %r.0, 0 ; This compare can be "replaced".
br i1 %cmp, label %if.then, label %if.end
if.then: br label %return
if.end: br label %return
return:
%retval.0 = phi i32 [ 100, %if.then ], [ %r.0, %if.end ]
ret i32 %retval.0
; CHECK-LABEL: @no_reuse_cmp2(
; CHECK: %r.0 = phi
; CHECK-NEXT: %cmp = icmp eq i32 %r.0, 0
; CHECK-NEXT: [[R:%.+]] = select i1 %cmp
; CHECK-NEXT: ret i32 [[R]]
}