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Enhance SRoA to promote allocas that are used by selects in some

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common cases.  This triggers a surprising number of times in SPEC2K6
because min/max idioms end up doing this.  For example, code from the
STL ends up looking like this to SRoA:

  %202 = load i64* %__old_size, align 8, !tbaa !3
  %203 = load i64* %__old_size, align 8, !tbaa !3
  %204 = load i64* %__n, align 8, !tbaa !3
  %205 = icmp ult i64 %203, %204
  %storemerge.i = select i1 %205, i64* %__n, i64* %__old_size
  %206 = load i64* %storemerge.i, align 8, !tbaa !3

We can now promote both the __n and the __old_size allocas.

This addresses another chunk of rdar://7339113, poor codegen on
stringswitch.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124088 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2011-01-23 22:04:55 +00:00
parent 3928af6ac4
commit c87c50a39c
2 changed files with 190 additions and 5 deletions
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62
test/Transforms/ScalarRepl/phi-select.ll
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@@ -44,16 +44,15 @@ F:
}
; CHECK: @test3
; CHECK: %A.0 = alloca i32
; CHECK: %A.1 = alloca i32
; CHECK-NEXT: %Q = select i1 %c, i32 1, i32 2
; CHECK-NEXT: ret i32 %Q
; rdar://8904039
define i32 @test3(i1 %c) {
entry:
%A = alloca {i32, i32}
%B = getelementptr {i32, i32}* %A, i32 0, i32 0
store i32 1, i32* %B
%C = getelementptr {i32, i32}* %A, i32 0, i32 1
store i32 2, i32* %B
store i32 2, i32* %C
%X = select i1 %c, i32* %B, i32* %C
%Q = load i32* %X
@@ -76,3 +75,58 @@ entry:
%Q = load i64* %Y
ret i64 %Q
}
;;
;; Tests for promoting allocas used by selects.
;; rdar://7339113
;;
define i32 @test5(i32 *%P) nounwind readnone ssp {
entry:
%b = alloca i32, align 8
store i32 2, i32* %b, align 8
;; Select on constant condition should be folded.
%p.0 = select i1 false, i32* %b, i32* %P
store i32 123, i32* %p.0
%r = load i32* %b, align 8
ret i32 %r
; CHECK: @test5
; CHECK: store i32 123, i32* %P
; CHECK: ret i32 2
}
define i32 @test6(i32 %x, i1 %c) nounwind readnone ssp {
%a = alloca i32, align 8
%b = alloca i32, align 8
store i32 1, i32* %a, align 8
store i32 2, i32* %b, align 8
%p.0 = select i1 %c, i32* %b, i32* %a
%r = load i32* %p.0, align 8
ret i32 %r
; CHECK: @test6
; CHECK-NEXT: %r = select i1 %c, i32 2, i32 1
; CHECK-NEXT: ret i32 %r
}
; Verify that the loads happen where the loads are, not where the select is.
define i32 @test7(i32 %x, i1 %c) nounwind readnone ssp {
%a = alloca i32, align 8
%b = alloca i32, align 8
store i32 1, i32* %a
store i32 2, i32* %b
%p.0 = select i1 %c, i32* %b, i32* %a
store i32 0, i32* %a
%r = load i32* %p.0, align 8
ret i32 %r
; CHECK: @test7
; CHECK-NOT: alloca i32
; CHECK: %r = select i1 %c, i32 2, i32 0
; CHECK: ret i32 %r
}