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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.

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