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JumpThreading: Turn a select instruction into branching if it allows to thread one half of the select.

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This is a common pattern coming out of simplifycfg generating gross code.

a:                                       ; preds = %entry
  %sel = select i1 %cmp1, double %add, double 0.000000e+00
  br label %b

b:
  %cond5 = phi double [ %sel, %a ], [ %sub, %entry ]
  %cmp6 = fcmp oeq double %cond5, 0.000000e+00
  br i1 %cmp6, label %if.then, label %if.end

becomes

a:
  br i1 %cmp1, label %b, label %if.then

b:
  %cond5 = phi double [ %sub, %entry ], [ %add, %a ]
  %cmp6 = fcmp oeq double %cond5, 0.000000e+00
  br i1 %cmp6, label %if.then, label %if.end

Skipping block b completely if possible.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187880 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer
2013-08-07 10:29:38 +00:00
parent e4a4aecffb
commit c11b107f21
2 changed files with 146 additions and 0 deletions
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63
test/Transforms/JumpThreading/select.ll
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@@ -157,3 +157,66 @@ L3:
L4:
ret void
}
define void @unfold1(double %x, double %y) nounwind {
entry:
%sub = fsub double %x, %y
%cmp = fcmp ogt double %sub, 1.000000e+01
br i1 %cmp, label %cond.end4, label %cond.false
cond.false: ; preds = %entry
%add = fadd double %x, %y
%cmp1 = fcmp ogt double %add, 1.000000e+01
%add. = select i1 %cmp1, double %add, double 0.000000e+00
br label %cond.end4
cond.end4: ; preds = %entry, %cond.false
%cond5 = phi double [ %add., %cond.false ], [ %sub, %entry ]
%cmp6 = fcmp oeq double %cond5, 0.000000e+00
br i1 %cmp6, label %if.then, label %if.end
if.then: ; preds = %cond.end4
call void @foo()
br label %if.end
if.end: ; preds = %if.then, %cond.end4
ret void
; CHECK-LABEL: @unfold1
; CHECK: br i1 %cmp, label %cond.end4, label %cond.false
; CHECK: br i1 %cmp1, label %cond.end4, label %if.then
; CHECK: br i1 %cmp6, label %if.then, label %if.end
; CHECK: br label %if.end
}
define void @unfold2(i32 %x, i32 %y) nounwind {
entry:
%sub = sub nsw i32 %x, %y
%cmp = icmp sgt i32 %sub, 10
br i1 %cmp, label %cond.end4, label %cond.false
cond.false: ; preds = %entry
%add = add nsw i32 %x, %y
%cmp1 = icmp sgt i32 %add, 10
%add. = select i1 %cmp1, i32 0, i32 %add
br label %cond.end4
cond.end4: ; preds = %entry, %cond.false
%cond5 = phi i32 [ %add., %cond.false ], [ %sub, %entry ]
%cmp6 = icmp eq i32 %cond5, 0
br i1 %cmp6, label %if.then, label %if.end
if.then: ; preds = %cond.end4
call void @foo()
br label %if.end
if.end: ; preds = %if.then, %cond.end4
ret void
; CHECK-LABEL: @unfold2
; CHECK: br i1 %cmp, label %if.end, label %cond.false
; CHECK: br i1 %cmp1, label %if.then, label %cond.end4
; CHECK: br i1 %cmp6, label %if.then, label %if.end
; CHECK: br label %if.end
}