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d777c2c0c0
If we know that the sign bit of a value being sign extended is zero, we can use a zero extension instead. This is motivated by the fact that zero extensions are generally cheaper on x86 (and most other architectures?). We already apply a similar transform in DAGCombine, this just extends that to the IR level. This comes up when we eagerly canonicalize gep indices to the width of a machine register (i64 on x86_64). To do so, we insert sign extensions (sext) to promote smaller types. Differential Revision: http://reviews.llvm.org/D7255 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229189 91177308-0d34-0410-b5e6-96231b3b80d8
62 lines
1.9 KiB
LLVM
62 lines
1.9 KiB
LLVM
; RUN: opt < %s -instcombine -S | FileCheck %s
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target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
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target triple = "x86_64-pc-win32"
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declare void @use(i32) readonly
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; We prefer to canonicalize the machine width gep indices early
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define void @test(i32* %p, i32 %index) {
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; CHECK-LABEL: @test
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; CHECK-NEXT: %1 = sext i32 %index to i64
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; CHECK-NEXT: %addr = getelementptr i32* %p, i64 %1
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%addr = getelementptr i32* %p, i32 %index
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%val = load i32* %addr
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call void @use(i32 %val)
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ret void
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}
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; If they've already been canonicalized via zext, that's fine
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define void @test2(i32* %p, i32 %index) {
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; CHECK-LABEL: @test2
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; CHECK-NEXT: %i = zext i32 %index to i64
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; CHECK-NEXT: %addr = getelementptr i32* %p, i64 %i
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%i = zext i32 %index to i64
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%addr = getelementptr i32* %p, i64 %i
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%val = load i32* %addr
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call void @use(i32 %val)
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ret void
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}
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; If we can use a zext, we prefer that. This requires
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; knowing that the index is positive.
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define void @test3(i32* %p, i32 %index) {
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; CHECK-LABEL: @test3
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; CHECK: zext
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; CHECK-NOT: sext
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%addr_begin = getelementptr i32* %p, i64 40
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%addr_fixed = getelementptr i32* %addr_begin, i64 48
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%val_fixed = load i32* %addr_fixed, !range !0
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%addr = getelementptr i32* %addr_begin, i32 %val_fixed
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%val = load i32* %addr
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call void @use(i32 %val)
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ret void
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}
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; Replace sext with zext where possible
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define void @test4(i32* %p, i32 %index) {
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; CHECK-LABEL: @test4
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; CHECK: zext
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; CHECK-NOT: sext
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%addr_begin = getelementptr i32* %p, i64 40
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%addr_fixed = getelementptr i32* %addr_begin, i64 48
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%val_fixed = load i32* %addr_fixed, !range !0
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%i = sext i32 %val_fixed to i64
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%addr = getelementptr i32* %addr_begin, i64 %i
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%val = load i32* %addr
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call void @use(i32 %val)
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ret void
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}
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;; !range !0
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!0 = !{i32 0, i32 2147483647}
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