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SimplifyCFG: Turn switches into sub+icmp+branch if possible.

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This makes the job of the later optzn passes easier, allowing the vast amount of
icmp transforms to chew on it.

We transform 840 switches in gcc.c, leading to a 16k byte shrink of the resulting
binary on i386-linux.

The testcase from README.txt now compiles into
  decl  %edi
  cmpl  $3, %edi
  sbbl  %eax, %eax
  andl  $1, %eax
  ret

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124724 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer
2011-02-02 15:56:22 +00:00
parent ff0c5014b2
commit 56442dfdcf
4 changed files with 39 additions and 70 deletions
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17
test/Transforms/SimplifyCFG/switch_create.ll
View File

@@ -141,14 +141,8 @@ UnifiedReturnBlock: ; preds = %shortcirc_done.4, %shortcirc_next.4
ret i1 %UnifiedRetVal
; CHECK: @test6
; CHECK: switch i32 %tmp.2.i, label %shortcirc_next.4 [
; CHECK: i32 14, label %UnifiedReturnBlock
; CHECK: i32 15, label %UnifiedReturnBlock
; CHECK: i32 16, label %UnifiedReturnBlock
; CHECK: i32 17, label %UnifiedReturnBlock
; CHECK: i32 18, label %UnifiedReturnBlock
; CHECK: i32 19, label %UnifiedReturnBlock
; CHECK: ]
; CHECK: %off = add i32 %tmp.2.i, -14
; CHECK: %switch = icmp ult i32 %off, 6
}
define void @test7(i8 zeroext %c, i32 %x) nounwind ssp noredzone {
@@ -447,11 +441,8 @@ if.end:
define zeroext i1 @test16(i32 %x) nounwind {
entry:
; CHECK: @test16
; CHECK: switch i32 %x, label %lor.rhs [
; CHECK: i32 1, label %lor.end
; CHECK: i32 2, label %lor.end
; CHECK: i32 3, label %lor.end
; CHECK: ]
; CHECK: %off = add i32 %x, -1
; CHECK: %switch = icmp ult i32 %off, 3
%cmp.i = icmp eq i32 %x, 1
br i1 %cmp.i, label %lor.end, label %lor.lhs.false

12
test/Transforms/SimplifyCFG/switch_formation.dbg.ll
View File

@@ -13,15 +13,9 @@
declare void @llvm.dbg.stoppoint(i32, i32, { }*) nounwind
define i1 @t({ i32, i32 }* %I) {
; CHECK: t
; CHECK: switch i32 %tmp.2.i, label %shortcirc_next.4 [
; CHECK: i32 14, label %UnifiedReturnBlock
; CHECK: i32 15, label %UnifiedReturnBlock
; CHECK: i32 16, label %UnifiedReturnBlock
; CHECK: i32 17, label %UnifiedReturnBlock
; CHECK: i32 18, label %UnifiedReturnBlock
; CHECK: i32 19, label %UnifiedReturnBlock
; CHECK: ]
; CHECK: @t
; CHECK: %off = add i32 %tmp.2.i, -14
; CHECK: %switch = icmp ult i32 %off, 6
entry:
%tmp.1.i = getelementptr { i32, i32 }* %I, i64 0, i32 1 ; <i32*> [#uses=1]
%tmp.2.i = load i32* %tmp.1.i ; <i32> [#uses=6]