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834ee28da9
Summary:
This pass sinks COPY instructions into a successor block, if the COPY is not
used in the current block and the COPY is live-in to a single successor
(i.e., doesn't require the COPY to be duplicated). This avoids executing the
the copy on paths where their results aren't needed. This also exposes
additional opportunites for dead copy elimination and shrink wrapping.
These copies were either not handled by or are inserted after the MachineSink
pass. As an example of the former case, the MachineSink pass cannot sink
COPY instructions with allocatable source registers; for AArch64 these type
of copy instructions are frequently used to move function parameters (PhyReg)
into virtual registers in the entry block..
For the machine IR below, this pass will sink %w19 in the entry into its
successor (%bb.1) because %w19 is only live-in in %bb.1.
```
%bb.0:
%wzr = SUBSWri %w1, 1
%w19 = COPY %w0
Bcc 11, %bb.2
%bb.1:
Live Ins: %w19
BL @fun
%w0 = ADDWrr %w0, %w19
RET %w0
%bb.2:
%w0 = COPY %wzr
RET %w0
```
As we sink %w19 (CSR in AArch64) into %bb.1, the shrink-wrapping pass will be
able to see %bb.0 as a candidate.
With this change I observed 12% more shrink-wrapping candidate and 13% more dead copies deleted in spec2000/2006/2017 on AArch64.
Reviewers: qcolombet, MatzeB, thegameg, mcrosier, gberry, hfinkel, john.brawn, twoh, RKSimon, sebpop, kparzysz
Reviewed By: sebpop
Subscribers: evandro, sebpop, sfertile, aemerson, mgorny, javed.absar, kristof.beyls, llvm-commits
Differential Revision: https://reviews.llvm.org/D41463
llvm-svn: 328237
159 lines
3.1 KiB
LLVM
159 lines
3.1 KiB
LLVM
; RUN: llc < %s -mtriple=thumbv7m -mcpu=cortex-m7 | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-BP
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; RUN: llc < %s -mtriple=thumbv7m -mcpu=cortex-m3 | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-NOBP
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declare void @otherfn()
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; CHECK-LABEL: triangle1:
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; CHECK: itt ne
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; CHECK: movne
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; CHECK: strne
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define i32 @triangle1(i32 %n, i32* %p) {
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entry:
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%tobool = icmp eq i32 %n, 0
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br i1 %tobool, label %if.end, label %if.then
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if.then:
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store i32 1, i32* %p, align 4
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br label %if.end
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if.end:
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tail call void @otherfn()
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ret i32 0
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}
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; CHECK-LABEL: triangle2:
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; CHECK-BP: itttt ne
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; CHECK-BP: movne
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; CHECK-BP: strne
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; CHECK-BP: movne
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; CHECK-BP: strne
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; CHECK-NOBP: cbz
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; CHECK-NOBP: movs
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; CHECK-NOBP: str
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; CHECK-NOBP: movs
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; CHECK-NOBP: str
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define i32 @triangle2(i32 %n, i32* %p, i32* %q) {
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entry:
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%tobool = icmp eq i32 %n, 0
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br i1 %tobool, label %if.end, label %if.then
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if.then:
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store i32 1, i32* %p, align 4
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store i32 2, i32* %q, align 4
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br label %if.end
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if.end:
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tail call void @otherfn()
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ret i32 0
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}
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; CHECK-LABEL: triangle3:
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; CHECK: cbz
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; CHECK: movs
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; CHECK: str
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; CHECK: movs
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; CHECK: str
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; CHECK: movs
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; CHECK: str
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define i32 @triangle3(i32 %n, i32* %p, i32* %q, i32* %r) {
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entry:
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%tobool = icmp eq i32 %n, 0
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br i1 %tobool, label %if.end, label %if.then
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if.then:
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store i32 1, i32* %p, align 4
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store i32 2, i32* %q, align 4
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store i32 3, i32* %r, align 4
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br label %if.end
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if.end:
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tail call void @otherfn()
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ret i32 0
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}
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; CHECK-LABEL: diamond1:
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; CHECK: itee eq
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; CHECK: ldreq
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; CHECK: strne
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define i32 @diamond1(i32 %n, i32* %p) {
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entry:
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%tobool = icmp eq i32 %n, 0
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br i1 %tobool, label %if.else, label %if.then
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if.then:
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store i32 %n, i32* %p, align 4
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br label %if.end
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if.else:
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%0 = load i32, i32* %p, align 4
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br label %if.end
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if.end:
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%n.addr.0 = phi i32 [ %n, %if.then ], [ %0, %if.else ]
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tail call void @otherfn()
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ret i32 %n.addr.0
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}
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; CHECK-LABEL: diamond2:
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; CHECK-BP: cbz
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; CHECK-BP: str
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; CHECK-BP: str
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; CHECK-BP: b
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; CHECK-BP: str
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; CHECK-BP: ldr
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; CHECK-NOBP: ittee
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; CHECK-NOBP: streq
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; CHECK-NOBP: ldreq
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; CHECK-NOBP: strne
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; CHECK-NOBP: strne
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define i32 @diamond2(i32 %n, i32* %p, i32* %q) {
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entry:
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%tobool = icmp eq i32 %n, 0
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br i1 %tobool, label %if.else, label %if.then
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if.then:
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store i32 %n, i32* %p, align 4
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%arrayidx = getelementptr inbounds i32, i32* %p, i32 2
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store i32 %n, i32* %arrayidx, align 4
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br label %if.end
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if.else:
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store i32 %n, i32* %q, align 4
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%0 = load i32, i32* %p, align 4
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br label %if.end
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if.end:
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%n.addr.0 = phi i32 [ %n, %if.then ], [ %0, %if.else ]
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tail call void @otherfn()
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ret i32 %n.addr.0
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}
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; CHECK-LABEL: diamond3:
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; CHECK: cbz
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; CHECK: movs
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; CHECK: str
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; CHECK: b
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; CHECK: ldr
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; CHECK: ldr
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; CHECK: adds
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define i32 @diamond3(i32 %n, i32* %p, i32* %q) {
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entry:
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%tobool = icmp eq i32 %n, 0
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br i1 %tobool, label %if.else, label %if.then
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if.then:
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store i32 1, i32* %p, align 4
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br label %if.end
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if.else:
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%0 = load i32, i32* %p, align 4
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%1 = load i32, i32* %q, align 4
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%add = add nsw i32 %1, %0
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br label %if.end
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if.end:
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%n.addr.0 = phi i32 [ %n, %if.then ], [ %add, %if.else ]
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tail call void @otherfn()
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ret i32 %n.addr.0
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}
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