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Don't create unnecessary PHIs

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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.

llvm-svn: 255489
This commit is contained in:
James Molloy 2015-12-14 10:57:01 +00:00
parent 1951f719df
commit 2b1e101e99
3 changed files with 205 additions and 4 deletions
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5
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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@ -2385,6 +2385,11 @@ static Value *ensureValueAvailableInSuccessor(Value *V, BasicBlock *BB,
// 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();

198
llvm/test/Transforms/SimplifyCFG/merge-cond-stores-2.ll Normal file
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@ -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
}

6
llvm/test/Transforms/SimplifyCFG/merge-cond-stores.ll
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@ -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