[SimplifyCFG] 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.

Now with a fix (and fixed tests) for the conformance issue seen in Chromium.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255767 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index ab281ef1edb8e78be37827d21959265eeb0a4d7c..d0932f834cf58328af94480140d71b4d6678f3fa 100644 (file)
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2419,6 +2419,11 @@ static Value *ensureValueAvailableInSuccessor(Value *V, BasicBlock *BB,
   if (PHI)
     return PHI;
 
+  // If V is not an instruction defined in BB, just return it.
+  if (!AlternativeV &&
+      (!isa<Instruction>(V) || cast<Instruction>(V)->getParent() != BB))
+    return V;
+
   PHI = PHINode::Create(V->getType(), 2, "simplifycfg.merge", &Succ->front());
   PHI->addIncoming(V, BB);
   for (BasicBlock *PredBB : predecessors(Succ))

diff --git a/test/Transforms/SimplifyCFG/merge-cond-stores-2.ll b/test/Transforms/SimplifyCFG/merge-cond-stores-2.ll
new file mode 100644 (file)
index 0000000..fe498b5
--- /dev/null
+++ b/test/Transforms/SimplifyCFG/merge-cond-stores-2.ll
@@ -0,0 +1,215 @@
+; 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
+; Exactly 15 phis, as there are 15 in the original test case.
+; CHECK: select
+; CHECK: select
+; CHECK: select
+; CHECK: select
+; CHECK: select
+; CHECK: select
+; CHECK: select
+; CHECK: select
+; CHECK: select
+; CHECK: select
+; CHECK: select
+; CHECK: select
+; CHECK: select
+; CHECK: select
+; CHECK: select
+; CHECK: select
+; CHECK-NOT: select
+; 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
+}