[llvm] r255489 - Don't create unnecessary PHIs
Hans Wennborg via llvm-commits
llvm-commits at lists.llvm.org
Mon Dec 14 13:33:00 PST 2015
On Mon, Dec 14, 2015 at 1:25 PM, Reid Kleckner via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> This change does not appear to respect the comments here:
> // If AlternativeV is not nullptr, we care about both incoming values in
> PHI.
> // PHI must be exactly: phi <ty> [ %BB, %V ], [ %OtherBB, %AlternativeV]
> // where OtherBB is the single other predecessor of BB's only successor.
>
> I suspect this change broke some Chromium tests. I'm in the process of
> reproducing the failure and testing if a revert fixes things.
Reverting locally fixes the Chromium test for me.
>
> On Mon, Dec 14, 2015 at 2:57 AM, James Molloy via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>>
>> Author: jamesm
>> Date: Mon Dec 14 04:57:01 2015
>> New Revision: 255489
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=255489&view=rev
>> Log:
>> Don't create unnecessary PHIs
>>
>> In conditional store merging, we were creating PHIs when we didn't
>> need to. If the value to be predicated isn't defined in the block
>> we're predicating, then it doesn't need a PHI at all (because we only
>> deal with triangles and diamonds, any value not in the predicated BB
>> must dominate the predicated BB).
>>
>> This fixes a large code size increase in some benchmarks in a popular
>> embedded benchmark suite.
>>
>> Added:
>> llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores-2.ll
>> Modified:
>> llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
>> llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores.ll
>>
>> Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=255489&r1=255488&r2=255489&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
>> +++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Mon Dec 14 04:57:01
>> 2015
>> @@ -2385,6 +2385,11 @@ static Value *ensureValueAvailableInSucc
>> // If AlternativeV is not nullptr, we care about both incoming values
>> in PHI.
>> // PHI must be exactly: phi <ty> [ %BB, %V ], [ %OtherBB,
>> %AlternativeV]
>> // where OtherBB is the single other predecessor of BB's only
>> successor.
>> +
>> + // If V is not an instruction defined in BB, just return it.
>> + if (!isa<Instruction>(V) || cast<Instruction>(V)->getParent() != BB)
>> + return V;
>> +
>> PHINode *PHI = nullptr;
>> BasicBlock *Succ = BB->getSingleSuccessor();
>>
>>
>> Added: llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores-2.ll
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores-2.ll?rev=255489&view=auto
>>
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores-2.ll (added)
>> +++ llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores-2.ll Mon Dec
>> 14 04:57:01 2015
>> @@ -0,0 +1,198 @@
>> +; RUN: opt -S < %s -simplifycfg -simplifycfg-merge-cond-stores=true
>> -simplifycfg-merge-cond-stores-aggressively=false
>> -phi-node-folding-threshold=2 | FileCheck %s
>> +
>> +target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
>> +target triple = "armv7--linux-gnueabihf"
>> +
>> +; This is a bit reversal that has been run through the early optimizer
>> (-mem2reg -gvn -instcombine).
>> +; There should be no additional PHIs created at all. The store should be
>> on its own in a predicated
>> +; block and there should be no PHIs.
>> +
>> +; CHECK-LABEL: @f
>> +; CHECK-NOT: phi
>> +; CHECK: br i1 {{.*}}, label %[[L:.*]], label %[[R:.*]]
>> +; CHECK: [[L]] ; preds =
>> +; CHECK-NEXT: store
>> +; CHECK-NEXT: br label %[[R]]
>> +; CHECK: [[R]] ; preds =
>> +; CHECK-NEXT: ret i32 0
>> +
>> +define i32 @f(i32* %b) {
>> +entry:
>> + %0 = load i32, i32* %b, align 4
>> + %and = and i32 %0, 1
>> + %tobool = icmp eq i32 %and, 0
>> + br i1 %tobool, label %if.end, label %if.then
>> +
>> +if.then: ; preds = %entry
>> + %or = or i32 %0, -2147483648
>> + store i32 %or, i32* %b, align 4
>> + br label %if.end
>> +
>> +if.end: ; preds = %entry,
>> %if.then
>> + %1 = phi i32 [ %0, %entry ], [ %or, %if.then ]
>> + %and1 = and i32 %1, 2
>> + %tobool2 = icmp eq i32 %and1, 0
>> + br i1 %tobool2, label %if.end5, label %if.then3
>> +
>> +if.then3: ; preds = %if.end
>> + %or4 = or i32 %1, 1073741824
>> + store i32 %or4, i32* %b, align 4
>> + br label %if.end5
>> +
>> +if.end5: ; preds = %if.end,
>> %if.then3
>> + %2 = phi i32 [ %1, %if.end ], [ %or4, %if.then3 ]
>> + %and6 = and i32 %2, 4
>> + %tobool7 = icmp eq i32 %and6, 0
>> + br i1 %tobool7, label %if.end10, label %if.then8
>> +
>> +if.then8: ; preds = %if.end5
>> + %or9 = or i32 %2, 536870912
>> + store i32 %or9, i32* %b, align 4
>> + br label %if.end10
>> +
>> +if.end10: ; preds = %if.end5,
>> %if.then8
>> + %3 = phi i32 [ %2, %if.end5 ], [ %or9, %if.then8 ]
>> + %and11 = and i32 %3, 8
>> + %tobool12 = icmp eq i32 %and11, 0
>> + br i1 %tobool12, label %if.end15, label %if.then13
>> +
>> +if.then13: ; preds = %if.end10
>> + %or14 = or i32 %3, 268435456
>> + store i32 %or14, i32* %b, align 4
>> + br label %if.end15
>> +
>> +if.end15: ; preds = %if.end10,
>> %if.then13
>> + %4 = phi i32 [ %3, %if.end10 ], [ %or14, %if.then13 ]
>> + %and16 = and i32 %4, 16
>> + %tobool17 = icmp eq i32 %and16, 0
>> + br i1 %tobool17, label %if.end20, label %if.then18
>> +
>> +if.then18: ; preds = %if.end15
>> + %or19 = or i32 %4, 134217728
>> + store i32 %or19, i32* %b, align 4
>> + br label %if.end20
>> +
>> +if.end20: ; preds = %if.end15,
>> %if.then18
>> + %5 = phi i32 [ %4, %if.end15 ], [ %or19, %if.then18 ]
>> + %and21 = and i32 %5, 32
>> + %tobool22 = icmp eq i32 %and21, 0
>> + br i1 %tobool22, label %if.end25, label %if.then23
>> +
>> +if.then23: ; preds = %if.end20
>> + %or24 = or i32 %5, 67108864
>> + store i32 %or24, i32* %b, align 4
>> + br label %if.end25
>> +
>> +if.end25: ; preds = %if.end20,
>> %if.then23
>> + %6 = phi i32 [ %5, %if.end20 ], [ %or24, %if.then23 ]
>> + %and26 = and i32 %6, 64
>> + %tobool27 = icmp eq i32 %and26, 0
>> + br i1 %tobool27, label %if.end30, label %if.then28
>> +
>> +if.then28: ; preds = %if.end25
>> + %or29 = or i32 %6, 33554432
>> + store i32 %or29, i32* %b, align 4
>> + br label %if.end30
>> +
>> +if.end30: ; preds = %if.end25,
>> %if.then28
>> + %7 = phi i32 [ %6, %if.end25 ], [ %or29, %if.then28 ]
>> + %and31 = and i32 %7, 256
>> + %tobool32 = icmp eq i32 %and31, 0
>> + br i1 %tobool32, label %if.end35, label %if.then33
>> +
>> +if.then33: ; preds = %if.end30
>> + %or34 = or i32 %7, 8388608
>> + store i32 %or34, i32* %b, align 4
>> + br label %if.end35
>> +
>> +if.end35: ; preds = %if.end30,
>> %if.then33
>> + %8 = phi i32 [ %7, %if.end30 ], [ %or34, %if.then33 ]
>> + %and36 = and i32 %8, 512
>> + %tobool37 = icmp eq i32 %and36, 0
>> + br i1 %tobool37, label %if.end40, label %if.then38
>> +
>> +if.then38: ; preds = %if.end35
>> + %or39 = or i32 %8, 4194304
>> + store i32 %or39, i32* %b, align 4
>> + br label %if.end40
>> +
>> +if.end40: ; preds = %if.end35,
>> %if.then38
>> + %9 = phi i32 [ %8, %if.end35 ], [ %or39, %if.then38 ]
>> + %and41 = and i32 %9, 1024
>> + %tobool42 = icmp eq i32 %and41, 0
>> + br i1 %tobool42, label %if.end45, label %if.then43
>> +
>> +if.then43: ; preds = %if.end40
>> + %or44 = or i32 %9, 2097152
>> + store i32 %or44, i32* %b, align 4
>> + br label %if.end45
>> +
>> +if.end45: ; preds = %if.end40,
>> %if.then43
>> + %10 = phi i32 [ %9, %if.end40 ], [ %or44, %if.then43 ]
>> + %and46 = and i32 %10, 2048
>> + %tobool47 = icmp eq i32 %and46, 0
>> + br i1 %tobool47, label %if.end50, label %if.then48
>> +
>> +if.then48: ; preds = %if.end45
>> + %or49 = or i32 %10, 1048576
>> + store i32 %or49, i32* %b, align 4
>> + br label %if.end50
>> +
>> +if.end50: ; preds = %if.end45,
>> %if.then48
>> + %11 = phi i32 [ %10, %if.end45 ], [ %or49, %if.then48 ]
>> + %and51 = and i32 %11, 4096
>> + %tobool52 = icmp eq i32 %and51, 0
>> + br i1 %tobool52, label %if.end55, label %if.then53
>> +
>> +if.then53: ; preds = %if.end50
>> + %or54 = or i32 %11, 524288
>> + store i32 %or54, i32* %b, align 4
>> + br label %if.end55
>> +
>> +if.end55: ; preds = %if.end50,
>> %if.then53
>> + %12 = phi i32 [ %11, %if.end50 ], [ %or54, %if.then53 ]
>> + %and56 = and i32 %12, 8192
>> + %tobool57 = icmp eq i32 %and56, 0
>> + br i1 %tobool57, label %if.end60, label %if.then58
>> +
>> +if.then58: ; preds = %if.end55
>> + %or59 = or i32 %12, 262144
>> + store i32 %or59, i32* %b, align 4
>> + br label %if.end60
>> +
>> +if.end60: ; preds = %if.end55,
>> %if.then58
>> + %13 = phi i32 [ %12, %if.end55 ], [ %or59, %if.then58 ]
>> + %and61 = and i32 %13, 16384
>> + %tobool62 = icmp eq i32 %and61, 0
>> + br i1 %tobool62, label %if.end65, label %if.then63
>> +
>> +if.then63: ; preds = %if.end60
>> + %or64 = or i32 %13, 131072
>> + store i32 %or64, i32* %b, align 4
>> + br label %if.end65
>> +
>> +if.end65: ; preds = %if.end60,
>> %if.then63
>> + %14 = phi i32 [ %13, %if.end60 ], [ %or64, %if.then63 ]
>> + %and66 = and i32 %14, 32768
>> + %tobool67 = icmp eq i32 %and66, 0
>> + br i1 %tobool67, label %if.end70, label %if.then68
>> +
>> +if.then68: ; preds = %if.end65
>> + %or69 = or i32 %14, 65536
>> + store i32 %or69, i32* %b, align 4
>> + br label %if.end70
>> +
>> +if.end70: ; preds = %if.end65,
>> %if.then68
>> + %15 = phi i32 [ %14, %if.end65 ], [ %or69, %if.then68 ]
>> + %and71 = and i32 %15, 128
>> + %tobool72 = icmp eq i32 %and71, 0
>> + br i1 %tobool72, label %if.end75, label %if.then73
>> +
>> +if.then73: ; preds = %if.end70
>> + %or74 = or i32 %15, 16777216
>> + store i32 %or74, i32* %b, align 4
>> + br label %if.end75
>> +
>> +if.end75: ; preds = %if.end70,
>> %if.then73
>> + ret i32 0
>> +}
>>
>> Modified: llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores.ll
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores.ll?rev=255489&r1=255488&r2=255489&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores.ll (original)
>> +++ llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores.ll Mon Dec 14
>> 04:57:01 2015
>> @@ -2,10 +2,8 @@
>>
>> ; CHECK-LABEL: @test_simple
>> ; This test should succeed and end up if-converted.
>> -; CHECK: icmp eq i32 %b, 0
>> -; CHECK-NEXT: icmp ne i32 %a, 0
>> -; CHECK-NEXT: xor i1 %x2, true
>> -; CHECK-NEXT: %[[x:.*]] = or i1 %{{.*}}, %{{.*}}
>> +; CHECK: %[[A:.*]] = or i32 %a, %b
>> +; CHECK-NEXT: %[[x:.*]] = icmp eq i32 %[[A]], 0
>> ; CHECK-NEXT: br i1 %[[x]]
>> ; CHECK: store
>> ; CHECK-NOT: store
>>
>>
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