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176c94be9c
This is an orthogonal and separated layer instead of being embedded inside the pass manager. While it adds a small amount of complexity, it is fairly minimal and the composability and control seems worth the cost. The logic for this ends up being nicely isolated and targeted. It should be easy to experiment with different iteration strategies wrapped around the CGSCC bottom-up walk using this kind of facility. The mechanism used to track devirtualization is the simplest one I came up with. I think it handles most of the cases the existing iteration machinery handles, but I haven't done a *very* in depth analysis. It does however match the basic intended semantics, and we can tweak or tune its exact behavior incrementally as necessary. One thing that we may want to revisit is freshly building the value handle set on each iteration. While I don't think this will be a significant cost (it is strictly fewer value handles but more churn of value handes than the old call graph), it is conceivable that we'll want a somewhat more clever tracking mechanism. My hope is to layer that on as a follow up patch with data supporting any implementation complexity it adds. This code also provides for a basic count heuristic: if the number of indirect calls decreases and the number of direct calls increases for a given function in the SCC, we assume devirtualization is responsible. This matches the heuristics currently used in the legacy pass manager. Differential Revision: https://reviews.llvm.org/D23114 llvm-svn: 290665
107 lines
3.2 KiB
LLVM
107 lines
3.2 KiB
LLVM
; Make sure that even without some external devirtualization iteration tool,
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; the CGSCC pass manager correctly observes and re-visits SCCs that change
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; structure due to devirtualization. We trigger devirtualization here with GVN
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; which forwards a store through a load and to an indirect call.
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;
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; RUN: opt -aa-pipeline=basic-aa -passes='cgscc(function-attrs)' -S < %s | FileCheck %s --check-prefix=BEFORE
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; RUN: opt -aa-pipeline=basic-aa -passes='cgscc(function-attrs,function(gvn))' -S < %s | FileCheck %s --check-prefix=AFTER
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;
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; Also check that adding an extra CGSCC pass after the function update but
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; without requiring the outer manager to iterate doesn't break any invariant.
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; RUN: opt -aa-pipeline=basic-aa -passes='cgscc(function-attrs,function(gvn),function-attrs)' -S < %s | FileCheck %s --check-prefix=AFTER
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declare void @readnone() readnone
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declare void @unknown()
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; The @test1_* checks that if we refine an indirect call to a direct call and
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; in the process change the very structure of the call graph we also revisit
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; that component of the graph and do so in an up-to-date fashion.
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; BEFORE: define void @test1_a1() {
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; AFTER: define void @test1_a1() {
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define void @test1_a1() {
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%fptr = alloca void()*
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store void()* @test1_b2, void()** %fptr
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store void()* @test1_b1, void()** %fptr
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%f = load void()*, void()** %fptr
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call void %f()
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ret void
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}
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; BEFORE: define void @test1_b1() {
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; AFTER: define void @test1_b1() {
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define void @test1_b1() {
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call void @unknown()
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call void @test1_a1()
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ret void
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}
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; BEFORE: define void @test1_a2() {
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; AFTER: define void @test1_a2() #0 {
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define void @test1_a2() {
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%fptr = alloca void()*
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store void()* @test1_b1, void()** %fptr
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store void()* @test1_b2, void()** %fptr
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%f = load void()*, void()** %fptr
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call void %f()
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ret void
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}
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; BEFORE: define void @test1_b2() {
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; AFTER: define void @test1_b2() #0 {
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define void @test1_b2() {
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call void @readnone()
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call void @test1_a2()
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ret void
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}
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; The @test2_* set of functions exercise a case where running function passes
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; introduces a new post-order relationship that was not present originally and
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; makes sure we walk across the SCCs in that order.
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; CHECK: define void @test2_a() {
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define void @test2_a() {
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call void @test2_b1()
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call void @test2_b2()
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call void @test2_b3()
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call void @unknown()
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ret void
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}
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; CHECK: define void @test2_b1() #0 {
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define void @test2_b1() {
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%fptr = alloca void()*
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store void()* @test2_a, void()** %fptr
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store void()* @readnone, void()** %fptr
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%f = load void()*, void()** %fptr
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call void %f()
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ret void
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}
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; CHECK: define void @test2_b2() #0 {
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define void @test2_b2() {
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%fptr = alloca void()*
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store void()* @test2_a, void()** %fptr
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store void()* @test2_b2, void()** %fptr
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store void()* @test2_b3, void()** %fptr
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store void()* @test2_b1, void()** %fptr
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%f = load void()*, void()** %fptr
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call void %f()
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ret void
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}
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; CHECK: define void @test2_b3() #0 {
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define void @test2_b3() {
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%fptr = alloca void()*
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store void()* @test2_a, void()** %fptr
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store void()* @test2_b2, void()** %fptr
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store void()* @test2_b3, void()** %fptr
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store void()* @test2_b1, void()** %fptr
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%f = load void()*, void()** %fptr
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call void %f()
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ret void
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}
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; CHECK: attributes #0 = { readnone }
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