[ThinLTO] Add funtions in callees metadata to CallGraphEdges
Summary:
If there's a callees metadata attached to the indirect call instruction, add CallGraphEdges to the callees mentioned in the metadata when computing FunctionSummary.
* Why this is necessary:
Consider following code example:
```
(foo.c)
static int f1(int x) {...}
static int f2(int x);
static int (*fptr)(int) = f2;
static int f2(int x) {
if (x) fptr=f1; return f1(x);
}
int foo(int x) {
(*fptr)(x); // !callees metadata of !{i32 (i32)* @f1, i32 (i32)* @f2} would be attached to this call.
}
(bar.c)
int bar(int x) {
return foo(x);
}
```
At LTO time when `foo.o` is imported into `bar.o`, function `foo` might be inlined into `bar` and PGO-guided indirect call promotion will run after that. If the profile data tells that the promotion of `@f1` or `@f2` is beneficial, the optimizer will check if the "promoted" `@f1` or `@f2` (such as `@f1.llvm.0` or `@f2.llvm.0`) is available. Without this patch, importing `!callees` metadata would only add promoted declarations of `@f1` and `@f2` to the `bar.o`, but still the optimizer will assume that the function is available and perform the promotion. The result of that is link failure with `undefined reference to @f1.llvm.0`.
This patch fixes this problem by adding callees in the `!callees` metadata to CallGraphEdges so that their definition would be properly imported into.
One may ask that there already is a logic to add indirect call promotion targets to be added to CallGraphEdges. However, if profile data says "indirect call promotion is only beneficial under a certain inline context", the logic wouldn't work. In the code example above, if profile data is like
```
bar:1000000:100000
1:100000
1: foo:100000
1: 100000 f1:100000
```
, Computing FunctionSummary for `foo.o` wouldn't add `foo->f1` to CallGraphEdges. (Also, it is at least "possible" that one can provide profile data to only link step but not to compilation step).
Reviewers: tejohnson, mehdi_amini, pcc
Reviewed By: tejohnson
Subscribers: inglorion, eraman, llvm-commits
Differential Revision: https://reviews.llvm.org/D44399
llvm-svn: 327358
2018-03-13 12:26:58 +08:00
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; Do setup work: generate bitcode and combined index
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; RUN: opt -module-summary %s -o %t1.bc
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; RUN: opt -module-summary %p/Inputs/callees-metadata.ll -o %t2.bc
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; RUN: llvm-lto2 run %t1.bc %t2.bc -o %t.o -save-temps \
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; RUN: -r=%t1.bc,bar,plx \
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; RUN: -r=%t1.bc,foo,l \
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; RUN: -r=%t2.bc,foo,pl
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; RUN: llvm-dis %t.o.1.3.import.bc -o - | FileCheck %s
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; CHECK: define {{.*}} i32 @f1.llvm.0
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; CHECK: define {{.*}} i32 @f2.llvm.0
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2019-09-11 07:15:38 +08:00
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target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
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[ThinLTO] Add funtions in callees metadata to CallGraphEdges
Summary:
If there's a callees metadata attached to the indirect call instruction, add CallGraphEdges to the callees mentioned in the metadata when computing FunctionSummary.
* Why this is necessary:
Consider following code example:
```
(foo.c)
static int f1(int x) {...}
static int f2(int x);
static int (*fptr)(int) = f2;
static int f2(int x) {
if (x) fptr=f1; return f1(x);
}
int foo(int x) {
(*fptr)(x); // !callees metadata of !{i32 (i32)* @f1, i32 (i32)* @f2} would be attached to this call.
}
(bar.c)
int bar(int x) {
return foo(x);
}
```
At LTO time when `foo.o` is imported into `bar.o`, function `foo` might be inlined into `bar` and PGO-guided indirect call promotion will run after that. If the profile data tells that the promotion of `@f1` or `@f2` is beneficial, the optimizer will check if the "promoted" `@f1` or `@f2` (such as `@f1.llvm.0` or `@f2.llvm.0`) is available. Without this patch, importing `!callees` metadata would only add promoted declarations of `@f1` and `@f2` to the `bar.o`, but still the optimizer will assume that the function is available and perform the promotion. The result of that is link failure with `undefined reference to @f1.llvm.0`.
This patch fixes this problem by adding callees in the `!callees` metadata to CallGraphEdges so that their definition would be properly imported into.
One may ask that there already is a logic to add indirect call promotion targets to be added to CallGraphEdges. However, if profile data says "indirect call promotion is only beneficial under a certain inline context", the logic wouldn't work. In the code example above, if profile data is like
```
bar:1000000:100000
1:100000
1: foo:100000
1: 100000 f1:100000
```
, Computing FunctionSummary for `foo.o` wouldn't add `foo->f1` to CallGraphEdges. (Also, it is at least "possible" that one can provide profile data to only link step but not to compilation step).
Reviewers: tejohnson, mehdi_amini, pcc
Reviewed By: tejohnson
Subscribers: inglorion, eraman, llvm-commits
Differential Revision: https://reviews.llvm.org/D44399
llvm-svn: 327358
2018-03-13 12:26:58 +08:00
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target triple = "x86_64-unknown-linux-gnu"
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define dso_local i32 @bar(i32 %x) {
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entry:
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%call = call i32 @foo(i32 %x)
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ret i32 %call
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}
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declare dso_local i32 @foo(i32)
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