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[GVN] Properly invalidate ICF cache when we simplify a value

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This fixes a "Cached first special instruction is wrong!" assert.

The assert fires because replacing a value with another can cause an
instruction to no longer be "special" to ICF. In this case,
devirtualization happened, turning an indirect call to a
call to a willreturn function which is no longer special.

Reviewed By: nikic, rnk

Differential Revision: https://reviews.llvm.org/D99977
This commit is contained in:
Arthur Eubanks 2021-04-08 11:44:23 -07:00
parent 7a43ae0368
commit 1debc51397
4 changed files with 67 additions and 0 deletions
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5
include/llvm/Analysis/InstructionPrecedenceTracking.h
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@ -80,6 +80,11 @@ public:
/// It makes all necessary updates to internal caches to keep them consistent.
void removeInstruction(const Instruction *Inst);
/// Notifies this tracking that we are going to replace all uses of \p Inst.
/// It makes all necessary updates to internal caches to keep them consistent.
/// Should typically be called before a RAUW.
void removeUsersOf(const Instruction *Inst);
/// Invalidates all information from this tracking.
void clear();
};

7
lib/Analysis/InstructionPrecedenceTracking.cpp
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@ -111,6 +111,13 @@ void InstructionPrecedenceTracking::removeInstruction(const Instruction *Inst) {
FirstSpecialInsts.erase(Inst->getParent());
}
void InstructionPrecedenceTracking::removeUsersOf(const Instruction *Inst) {
for (const auto *U : Inst->users()) {
if (const auto *UI = dyn_cast<Instruction>(U))
removeInstruction(UI);
}
}
void InstructionPrecedenceTracking::clear() {
FirstSpecialInsts.clear();
#ifndef NDEBUG

3
lib/Transforms/Scalar/GVN.cpp
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@ -2168,6 +2168,9 @@ bool GVN::processInstruction(Instruction *I) {
if (Value *V = SimplifyInstruction(I, {DL, TLI, DT, AC})) {
bool Changed = false;
if (!I->use_empty()) {
// Simplification can cause a special instruction to become not special.
// For example, devirtualization to a willreturn function.
ICF->removeUsersOf(I);
I->replaceAllUsesWith(V);
Changed = true;
}

52
test/Transforms/GVN/simplify-icf-cache-invalidation.ll Normal file
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@ -0,0 +1,52 @@
; RUN: opt -passes=gvn -S < %s | FileCheck %s
; CHECK: define {{.*}}@eggs
%struct.zot = type { i32 (...)** }
%struct.wombat = type { i8* }
%struct.baz = type { i8, i8* }
@global = hidden unnamed_addr constant i8* bitcast (void (%struct.zot*, i1)* @quux to i8*)
declare i8* @f()
define hidden void @eggs(%struct.zot* %arg, i1 %arg2, i32* %arg3, i32 %arg4, %struct.baz** %arg5) unnamed_addr align 2 {
bb:
%tmp = alloca %struct.wombat, align 8
%tmp1 = getelementptr %struct.zot, %struct.zot* %arg, i64 0, i32 0
store i32 (...)** bitcast (i8** @global to i32 (...)**), i32 (...)*** %tmp1, align 8, !invariant.group !0
br i1 %arg2, label %bb4, label %bb2
bb2: ; preds = %bb
%tmp3 = atomicrmw sub i32* %arg3, i32 %arg4 acq_rel, align 4
br label %bb4
bb4: ; preds = %bb2, %bb
%tmp5 = load %struct.baz*, %struct.baz** %arg5, align 8
%tmp6 = getelementptr inbounds %struct.baz, %struct.baz* %tmp5, i64 0, i32 1
br i1 %arg2, label %bb9, label %bb7
bb7: ; preds = %bb4
%tmp8 = tail call i8* @f()
br label %bb9
bb9: ; preds = %bb7, %bb4
%tmp10 = load %struct.baz*, %struct.baz** %arg5, align 8
%tmp11 = getelementptr inbounds %struct.baz, %struct.baz* %tmp10, i64 0, i32 0
%tmp12 = bitcast %struct.zot* %arg to void (%struct.zot*, i1)***
%tmp13 = load void (%struct.zot*, i1)**, void (%struct.zot*, i1)*** %tmp12, align 8, !invariant.group !0
%tmp14 = getelementptr inbounds void (%struct.zot*, i1)*, void (%struct.zot*, i1)** %tmp13, i64 0
%tmp15 = load void (%struct.zot*, i1)*, void (%struct.zot*, i1)** %tmp14, align 8
tail call void %tmp15(%struct.zot* %arg, i1 %arg2)
%tmp16 = getelementptr inbounds %struct.wombat, %struct.wombat* %tmp, i64 0, i32 0
%tmp17 = load i8*, i8** %tmp16, align 8
%tmp18 = icmp eq i8* %tmp17, null
ret void
}
; Function Attrs: nounwind willreturn
declare hidden void @quux(%struct.zot*, i1) unnamed_addr #0 align 2
attributes #0 = { nounwind willreturn }
!0 = !{}