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fix a fairly serious oversight with switch formation from

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or'd conditions.  Previously we'd compile something like this:

int crud (unsigned char c) {
   return c == 62 || c == 34 || c == 92;
}

into:

  switch i8 %c, label %lor.rhs [
    i8 62, label %lor.end
    i8 34, label %lor.end
  ]

lor.rhs:                                          ; preds = %entry
  %cmp8 = icmp eq i8 %c, 92
  br label %lor.end

lor.end:                                          ; preds = %entry, %entry, %lor.rhs
  %0 = phi i1 [ true, %entry ], [ %cmp8, %lor.rhs ], [ true, %entry ]
  %lor.ext = zext i1 %0 to i32
  ret i32 %lor.ext

which failed to merge the compare-with-92 into the switch.  With this patch
we simplify this all the way to:

  switch i8 %c, label %lor.rhs [
    i8 62, label %lor.end
    i8 34, label %lor.end
    i8 92, label %lor.end
  ]

lor.rhs:                                          ; preds = %entry
  br label %lor.end

lor.end:                                          ; preds = %entry, %entry, %entry, %lor.rhs
  %0 = phi i1 [ true, %entry ], [ false, %lor.rhs ], [ true, %entry ], [ true, %entry ]
  %lor.ext = zext i1 %0 to i32
  ret i32 %lor.ext

which is much better for codegen's switch lowering stuff.  This kicks in 33 times
on 176.gcc (for example) cutting 103 instructions off the generated code.





git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121671 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2010-12-13 03:18:54 +00:00
parent e991b5fdd5
commit 61c77449c7
2 changed files with 141 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

45
test/Transforms/SimplifyCFG/switch_create.ll
View File

@@ -1,4 +1,4 @@
; RUN: opt < %s -simplifycfg -S | not grep br
; RUN: opt < %s -simplifycfg -S | FileCheck %s
declare void @foo1()
@@ -15,6 +15,11 @@ T: ; preds = %0
F: ; preds = %0
call void @foo2( )
ret void
; CHECK: @test1
; CHECK: switch i32 %V, label %F [
; CHECK: i32 17, label %T
; CHECK: i32 4, label %T
; CHECK: ]
}
define void @test2(i32 %V) {
@@ -28,6 +33,11 @@ T: ; preds = %0
F: ; preds = %0
call void @foo2( )
ret void
; CHECK: @test2
; CHECK: switch i32 %V, label %T [
; CHECK: i32 17, label %F
; CHECK: i32 4, label %F
; CHECK: ]
}
define void @test3(i32 %V) {
@@ -42,6 +52,39 @@ T: ; preds = %N, %0
F: ; preds = %N
call void @foo2( )
ret void
; CHECK: @test3
; CHECK: switch i32 %V, label %F [
; CHECK: i32 4, label %T
; CHECK: i32 17, label %T
; CHECK: ]
}
define i32 @test4(i8 zeroext %c) nounwind ssp noredzone {
entry:
%cmp = icmp eq i8 %c, 62
br i1 %cmp, label %lor.end, label %lor.lhs.false
lor.lhs.false: ; preds = %entry
%cmp4 = icmp eq i8 %c, 34
br i1 %cmp4, label %lor.end, label %lor.rhs
lor.rhs: ; preds = %lor.lhs.false
%cmp8 = icmp eq i8 %c, 92
br label %lor.end
lor.end: ; preds = %lor.rhs, %lor.lhs.false, %entry
%0 = phi i1 [ true, %lor.lhs.false ], [ true, %entry ], [ %cmp8, %lor.rhs ]
%lor.ext = zext i1 %0 to i32
ret i32 %lor.ext
; CHECK: @test4
; CHECK: switch i8 %c, label %lor.rhs [
; CHECK: i8 62, label %lor.end
; CHECK: i8 34, label %lor.end
; CHECK: i8 92, label %lor.end
; CHECK: ]
}