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60150a3256
Summary: Add a dominance check to ensure that the possible devirtualizable call is actually dominated by the type test/checked load intrinsic being analyzed. With PGO, after indirect call promotion is performed during the compile step, followed by inlining, we may have a type test in the promoted and inlined sequence that allows an indirect call in that sequence to be devirtualized. That indirect call (inserted by inlining after promotion) will share the same vtable pointer as the fallback indirect call that cannot be devirtualized. Before this patch the code was incorrectly devirtualizing the fallback indirect call. See the new test and the example described there for more details. Reviewers: pcc, vitalybuka Subscribers: mehdi_amini, Prazek, eraman, steven_wu, dexonsmith, llvm-commits Differential Revision: https://reviews.llvm.org/D52514 llvm-svn: 343226
149 lines
5.8 KiB
LLVM
149 lines
5.8 KiB
LLVM
; REQUIRES: x86-registered-target
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; Test devirtualization through the thin link and backend, ensuring that
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; it is only applied when the type test corresponding to a devirtualization
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; dominates an indirect call using the same vtable pointer. Indirect
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; call promotion and inlining may introduce a guarded indirect call
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; that can be promoted, which uses the same vtable address as the fallback
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; indirect call that cannot be devirtualized.
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; The code below illustrates the structure when we started with code like:
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;
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; class A {
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; public:
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; virtual int foo() { return 1; }
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; virtual int bar() { return 1; }
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; };
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; class B : public A {
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; public:
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; virtual int foo();
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; virtual int bar();
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; };
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;
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; int foo(A *a) {
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; return a->foo(); // ICP profile says most calls are to B::foo()
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; }
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;
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; int B::foo() {
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; return bar();
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; }
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;
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; After the compile step, which will perform ICP and a round of inlining, we
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; have something like:
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; int foo(A *a) {
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; if (&a->foo() == B::foo())
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; return ((B*)a)->bar(); // Inlined from promoted direct call to B::foo()
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; else
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; return a->foo();
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;
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; The inlined code seqence will have a type test against "_ZTS1B",
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; which will allow us to devirtualize indirect call ((B*)a)->bar() to B::bar();
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; Both that type test and the one for the fallback a->foo() indirect call
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; will use the same vtable pointer. Without a dominance check, we could
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; incorrectly devirtualize a->foo() to B::foo();
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; RUN: opt -thinlto-bc -o %t.o %s
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; Legacy PM
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; RUN: llvm-lto2 run %t.o -save-temps -pass-remarks=. \
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; RUN: -o %t3 \
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; RUN: -r=%t.o,_Z3bazP1A,px \
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; RUN: -r=%t.o,_ZN1A3fooEv, \
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; RUN: -r=%t.o,_ZN1A3barEv, \
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; RUN: -r=%t.o,_ZN1B3fooEv, \
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; RUN: -r=%t.o,_ZN1B3barEv, \
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; RUN: -r=%t.o,_ZTV1A, \
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; RUN: -r=%t.o,_ZTV1B, \
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; RUN: -r=%t.o,_ZN1A3fooEv, \
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; RUN: -r=%t.o,_ZN1A3barEv, \
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; RUN: -r=%t.o,_ZN1B3fooEv, \
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; RUN: -r=%t.o,_ZN1B3barEv, \
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; RUN: -r=%t.o,_ZTV1A,px \
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; RUN: -r=%t.o,_ZTV1B,px 2>&1 | FileCheck %s --check-prefix=REMARK
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; RUN: llvm-dis %t3.1.4.opt.bc -o - | FileCheck %s --check-prefix=CHECK-IR
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; New PM
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; RUN: llvm-lto2 run %t.o -save-temps -use-new-pm -pass-remarks=. \
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; RUN: -o %t3 \
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; RUN: -r=%t.o,_Z3bazP1A,px \
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; RUN: -r=%t.o,_ZN1A3fooEv, \
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; RUN: -r=%t.o,_ZN1A3barEv, \
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; RUN: -r=%t.o,_ZN1B3fooEv, \
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; RUN: -r=%t.o,_ZN1B3barEv, \
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; RUN: -r=%t.o,_ZTV1A, \
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; RUN: -r=%t.o,_ZTV1B, \
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; RUN: -r=%t.o,_ZN1A3fooEv, \
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; RUN: -r=%t.o,_ZN1A3barEv, \
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; RUN: -r=%t.o,_ZN1B3fooEv, \
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; RUN: -r=%t.o,_ZN1B3barEv, \
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; RUN: -r=%t.o,_ZTV1A,px \
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; RUN: -r=%t.o,_ZTV1B,px 2>&1 | FileCheck %s --check-prefix=REMARK
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; RUN: llvm-dis %t3.1.4.opt.bc -o - | FileCheck %s --check-prefix=CHECK-IR
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; We should only devirtualize the inlined call to bar().
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; REMARK-NOT: single-impl: devirtualized a call to _ZN1B3fooEv
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; REMARK: single-impl: devirtualized a call to _ZN1B3barEv
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; REMARK-NOT: single-impl: devirtualized a call to _ZN1B3fooEv
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-grtev4-linux-gnu"
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%class.A = type { i32 (...)** }
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%class.B = type { %class.A }
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@_ZTV1A = linkonce_odr hidden unnamed_addr constant { [4 x i8*] } { [4 x i8*] [i8* null, i8* undef, i8* bitcast (i32 (%class.A*)* @_ZN1A3fooEv to i8*), i8* bitcast (i32 (%class.A*)* @_ZN1A3barEv to i8*)] }, align 8, !type !0
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@_ZTV1B = hidden unnamed_addr constant { [4 x i8*] } { [4 x i8*] [i8* null, i8* undef, i8* bitcast (i32 (%class.B*)* @_ZN1B3fooEv to i8*), i8* bitcast (i32 (%class.B*)* @_ZN1B3barEv to i8*)] }, align 8, !type !0, !type !1
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define hidden i32 @_Z3bazP1A(%class.A* %a) local_unnamed_addr {
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entry:
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%0 = bitcast %class.A* %a to i32 (%class.A*)***
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%vtable = load i32 (%class.A*)**, i32 (%class.A*)*** %0, align 8
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%1 = bitcast i32 (%class.A*)** %vtable to i8*
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%2 = tail call i1 @llvm.type.test(i8* %1, metadata !"_ZTS1A")
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tail call void @llvm.assume(i1 %2)
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%3 = load i32 (%class.A*)*, i32 (%class.A*)** %vtable, align 8
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; This is the compare instruction inserted by ICP
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%4 = icmp eq i32 (%class.A*)* %3, bitcast (i32 (%class.B*)* @_ZN1B3fooEv to i32 (%class.A*)*)
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br i1 %4, label %if.true.direct_targ, label %if.false.orig_indirect
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; This block contains the promoted and inlined call to B::foo();
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; CHECK-IR: if.true.direct_targ: ; preds = %entry
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if.true.direct_targ: ; preds = %entry
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%5 = bitcast %class.A* %a to %class.B*
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%6 = bitcast i32 (%class.A*)** %vtable to i8*
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%7 = tail call i1 @llvm.type.test(i8* %6, metadata !"_ZTS1B")
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tail call void @llvm.assume(i1 %7)
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%vfn.i1 = getelementptr inbounds i32 (%class.A*)*, i32 (%class.A*)** %vtable, i64 1
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%vfn.i = bitcast i32 (%class.A*)** %vfn.i1 to i32 (%class.B*)**
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%8 = load i32 (%class.B*)*, i32 (%class.B*)** %vfn.i, align 8
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; Call to bar() can be devirtualized to call to B::bar(), since it was
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; inlined from B::foo() after ICP introduced the guarded promotion.
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; CHECK-IR: %call.i = tail call i32 @_ZN1B3barEv(%class.B* %3)
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%call.i = tail call i32 %8(%class.B* %5)
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br label %if.end.icp
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; This block contains the fallback indirect call a->foo()
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; CHECK-IR: if.false.orig_indirect:
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if.false.orig_indirect: ; preds = %entry
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; Fallback indirect call to foo() cannot be devirtualized.
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; CHECK-IR: %call = tail call i32 %
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%call = tail call i32 %3(%class.A* nonnull %a)
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br label %if.end.icp
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if.end.icp: ; preds = %if.false.orig_indirect, %if.true.direct_targ
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%9 = phi i32 [ %call, %if.false.orig_indirect ], [ %call.i, %if.true.direct_targ ]
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ret i32 %9
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}
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declare i1 @llvm.type.test(i8*, metadata)
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declare void @llvm.assume(i1)
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declare dso_local i32 @_ZN1B3fooEv(%class.B* %this) unnamed_addr
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declare dso_local i32 @_ZN1B3barEv(%class.B*) unnamed_addr
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declare dso_local i32 @_ZN1A3barEv(%class.A* %this) unnamed_addr
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declare dso_local i32 @_ZN1A3fooEv(%class.A* %this) unnamed_addr
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!0 = !{i64 16, !"_ZTS1A"}
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!1 = !{i64 16, !"_ZTS1B"}
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