6db9ff64a8
This patch contains a pass that transforms CBZ/CBNZ/TBZ/TBNZ instructions into a conditional branch (Bcc), when the NZCV flags can be set for "free". This is preferred on targets that have more flexibility when scheduling Bcc instructions as compared to CBZ/CBNZ/TBZ/TBNZ (assuming all other variables are equal). This can reduce register pressure and is also the default behavior for GCC. A few examples: add w8, w0, w1 -> cmn w0, w1 ; CMN is an alias of ADDS. cbz w8, .LBB_2 -> b.eq .LBB0_2 ; single def/use of w8 removed. add w8, w0, w1 -> adds w8, w0, w1 ; w8 has multiple uses. cbz w8, .LBB1_2 -> b.eq .LBB1_2 sub w8, w0, w1 -> subs w8, w0, w1 ; w8 has multiple uses. tbz w8, #31, .LBB6_2 -> b.ge .LBB6_2 In looking at all current sub-target machine descriptions, this transformation appears to be either positive or neutral. Differential Revision: https://reviews.llvm.org/D34220. llvm-svn: 306144
61 lines
1.5 KiB
LLVM
61 lines
1.5 KiB
LLVM
; RUN: llc -mtriple=aarch64-linux-gnu -verify-machineinstrs -o - %s | FileCheck %s
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@x = thread_local local_unnamed_addr global i32 0, align 4
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@y = thread_local local_unnamed_addr global i32 0, align 4
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; Machine LICM should hoist the mrs into the loop preheader.
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; CHECK-LABEL: @test1
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; CHECK: BB#1:
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; CHECK: mrs x[[BASE:[0-9]+]], TPIDR_EL0
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; CHECK: add x[[REG1:[0-9]+]], x[[BASE]], :tprel_hi12:x
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; CHECK: add x[[REG2:[0-9]+]], x[[REG1]], :tprel_lo12_nc:x
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;
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; CHECK: .LBB0_2:
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; CHECK: ldr w0, [x[[REG2]]]
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; CHECK: bl bar
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; CHECK: subs w[[REG3:[0-9]+]], w{{[0-9]+}}, #1
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; CHECK: b.ne .LBB0_2
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define void @test1(i32 %n) local_unnamed_addr {
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entry:
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%cmp3 = icmp sgt i32 %n, 0
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br i1 %cmp3, label %bb1, label %bb2
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bb1:
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br label %for.body
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for.body:
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%i.04 = phi i32 [ %inc, %for.body ], [ 0, %bb1 ]
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%0 = load i32, i32* @x, align 4
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tail call void @bar(i32 %0) #2
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%inc = add nuw nsw i32 %i.04, 1
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%exitcond = icmp eq i32 %inc, %n
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br i1 %exitcond, label %bb2, label %for.body
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bb2:
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ret void
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}
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; Machine CSE should combine the the mrs between the load of %x and %y.
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; CHECK-LABEL: @test2
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; CHECK: mrs x{{[0-9]+}}, TPIDR_EL0
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; CHECK-NOT: mrs x{{[0-9]+}}, TPIDR_EL0
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; CHECK: ret
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define void @test2(i32 %c) local_unnamed_addr #0 {
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entry:
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%0 = load i32, i32* @x, align 4
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tail call void @bar(i32 %0) #2
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%cmp = icmp eq i32 %c, 0
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br i1 %cmp, label %if.end, label %if.then
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if.then:
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%1 = load i32, i32* @y, align 4
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tail call void @bar(i32 %1) #2
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br label %if.end
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if.end:
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ret void
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}
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declare void @bar(i32) local_unnamed_addr
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