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improve switch formation to handle small range

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comparisons formed by comparisons.  For example,
this:

void foo(unsigned x) {
  if (x == 0 || x == 1 || x == 3 || x == 4 || x == 6) 
    bar();
}

compiles into:

_foo:                                   ## @foo
## BB#0:                                ## %entry
	cmpl	$6, %edi
	ja	LBB0_2
## BB#1:                                ## %entry
	movl	%edi, %eax
	movl	$91, %ecx
	btq	%rax, %rcx
	jb	LBB0_3

instead of:

_foo:                                   ## @foo
## BB#0:                                ## %entry
	cmpl	$2, %edi
	jb	LBB0_4
## BB#1:                                ## %switch.early.test
	cmpl	$6, %edi
	ja	LBB0_3
## BB#2:                                ## %switch.early.test
	movl	%edi, %eax
	movl	$88, %ecx
	btq	%rax, %rcx
	jb	LBB0_4

This catches a bunch of cases in GCC, which look like this:

 %804 = load i32* @which_alternative, align 4, !tbaa !0
 %805 = icmp ult i32 %804, 2
 %806 = icmp eq i32 %804, 3
 %or.cond121 = or i1 %805, %806
 %807 = icmp eq i32 %804, 4
 %or.cond124 = or i1 %or.cond121, %807
 br i1 %or.cond124, label %.thread, label %808

turning this into a range comparison.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122045 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2010-12-17 06:20:15 +00:00
parent 1139d5090a
commit e27db74a60
3 changed files with 96 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files
test/Transforms/SimplifyCFG/switch_create.ll
+70 -1
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@@ -351,4 +351,73 @@ malformed:
ret void
; CHECK: @test12
}
}
; test13 - handle switch formation with ult.
define void @test13(i32 %x) nounwind ssp noredzone {
entry:
%cmp = icmp ult i32 %x, 2
br i1 %cmp, label %if.then, label %lor.lhs.false3
lor.lhs.false3: ; preds = %lor.lhs.false
%cmp5 = icmp eq i32 %x, 3
br i1 %cmp5, label %if.then, label %lor.lhs.false6
lor.lhs.false6: ; preds = %lor.lhs.false3
%cmp8 = icmp eq i32 %x, 4
br i1 %cmp8, label %if.then, label %lor.lhs.false9
lor.lhs.false9: ; preds = %lor.lhs.false6
%cmp11 = icmp eq i32 %x, 6
br i1 %cmp11, label %if.then, label %if.end
if.then: ; preds = %lor.lhs.false9, %lor.lhs.false6, %lor.lhs.false3, %lor.lhs.false, %entry
call void @foo1() noredzone
br label %if.end
if.end: ; preds = %if.then, %lor.lhs.false9
ret void
; CHECK: @test13
; CHECK: switch i32 %x, label %if.end [
; CHECK: i32 6, label %if.then
; CHECK: i32 4, label %if.then
; CHECK: i32 3, label %if.then
; CHECK: i32 1, label %if.then
; CHECK: i32 0, label %if.then
; CHECK: ]
}
; test14 - handle switch formation with ult.
define void @test14(i32 %x) nounwind ssp noredzone {
entry:
%cmp = icmp ugt i32 %x, 2
br i1 %cmp, label %lor.lhs.false3, label %if.then
lor.lhs.false3: ; preds = %lor.lhs.false
%cmp5 = icmp ne i32 %x, 3
br i1 %cmp5, label %lor.lhs.false6, label %if.then
lor.lhs.false6: ; preds = %lor.lhs.false3
%cmp8 = icmp ne i32 %x, 4
br i1 %cmp8, label %lor.lhs.false9, label %if.then
lor.lhs.false9: ; preds = %lor.lhs.false6
%cmp11 = icmp ne i32 %x, 6
br i1 %cmp11, label %if.end, label %if.then
if.then: ; preds = %lor.lhs.false9, %lor.lhs.false6, %lor.lhs.false3, %lor.lhs.false, %entry
call void @foo1() noredzone
br label %if.end
if.end: ; preds = %if.then, %lor.lhs.false9
ret void
; CHECK: @test14
; CHECK: switch i32 %x, label %if.end [
; CHECK: i32 6, label %if.then
; CHECK: i32 4, label %if.then
; CHECK: i32 3, label %if.then
; CHECK: i32 1, label %if.then
; CHECK: i32 0, label %if.then
; CHECK: ]
}