[PATCH] D104798: [WPD] Don't optimize calls more than once

[Arthur Eubanks via Phabricator via llvm-commits]

aeubanks created this revision.
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WPD currently assumes that each vtable load corresponds to one virtual
call. However, with -fstrict-vtable-pointers this may not be true. This
ends up causing crashes when we try to optimize a virtual call more than
once (e.g. applyUniformRetValOpt()/applyUniqueRetValOpt()/applyVirtualConstProp()).

This makes Chrome successfully build with -fstrict-vtable-pointers + WPD.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D104798

Files:
  llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
  llvm/test/Transforms/WholeProgramDevirt/virtual-const-prop-multiple-assumes.ll


Index: llvm/test/Transforms/WholeProgramDevirt/virtual-const-prop-multiple-assumes.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/WholeProgramDevirt/virtual-const-prop-multiple-assumes.ll
@@ -0,0 +1,43 @@
+; RUN: opt -S -wholeprogramdevirt -whole-program-visibility %s | FileCheck %s
+
+target datalayout = "e-p:64:64"
+target triple = "x86_64-unknown-linux-gnu"
+
+ at vt2 = constant [3 x i8*] [
+i8* bitcast (i1 (i8*)* @vf1i1 to i8*),
+i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
+i8* bitcast (i32 (i8*)* @vf2i32 to i8*)
+], !type !0
+
+define i1 @vf0i1(i8* %this) readnone {
+  ret i1 0
+}
+
+define i1 @vf1i1(i8* %this) readnone {
+  ret i1 1
+}
+
+define i32 @vf2i32(i8* %this) readnone {
+  ret i32 2
+}
+
+; CHECK: define i1 @call1(
+define i1 @call1(i8* %obj) {
+  %vtableptr = bitcast i8* %obj to [3 x i8*]**
+  %vtable = load [3 x i8*]*, [3 x i8*]** %vtableptr
+  %vtablei8 = bitcast [3 x i8*]* %vtable to i8*
+  %p = call i1 @llvm.type.test(i8* %vtablei8, metadata !"typeid")
+  call void @llvm.assume(i1 %p)
+  %p2 = call i1 @llvm.type.test(i8* %vtablei8, metadata !"typeid")
+  call void @llvm.assume(i1 %p2)
+  %fptrptr = getelementptr [3 x i8*], [3 x i8*]* %vtable, i32 0, i32 0
+  %fptr = load i8*, i8** %fptrptr
+  %fptr_casted = bitcast i8* %fptr to i1 (i8*)*
+  %result = call i1 %fptr_casted(i8* %obj)
+  ret i1 %result
+}
+
+declare i1 @llvm.type.test(i8*, metadata)
+declare void @llvm.assume(i1)
+
+!0 = !{i32 0, !"typeid"}
\ No newline at end of file
Index: llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
===================================================================
--- llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
+++ llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
@@ -518,6 +518,11 @@
 
   MapVector<VTableSlot, VTableSlotInfo> CallSlots;
 
+  // Calls that have already been optimized. We may add a call to multiple
+  // VTableSlotInfos if vtable loads are coalesced and need to make sure not to
+  // optimize a call more than once.
+  SmallPtrSet<CallBase *, 8> OptimizedCalls;
+
   // This map keeps track of the number of "unsafe" uses of a loaded function
   // pointer. The key is the associated llvm.type.test intrinsic call generated
   // by this pass. An unsafe use is one that calls the loaded function pointer
@@ -1406,10 +1411,13 @@
 
 void DevirtModule::applyUniformRetValOpt(CallSiteInfo &CSInfo, StringRef FnName,
                                          uint64_t TheRetVal) {
-  for (auto Call : CSInfo.CallSites)
+  for (auto Call : CSInfo.CallSites) {
+    if (!OptimizedCalls.insert(&Call.CB).second)
+      continue;
     Call.replaceAndErase(
         "uniform-ret-val", FnName, RemarksEnabled, OREGetter,
         ConstantInt::get(cast<IntegerType>(Call.CB.getType()), TheRetVal));
+  }
   CSInfo.markDevirt();
 }
 
@@ -1515,6 +1523,8 @@
                                         bool IsOne,
                                         Constant *UniqueMemberAddr) {
   for (auto &&Call : CSInfo.CallSites) {
+    if (!OptimizedCalls.insert(&Call.CB).second)
+      continue;
     IRBuilder<> B(&Call.CB);
     Value *Cmp =
         B.CreateICmp(IsOne ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE, Call.VTable,
@@ -1583,6 +1593,8 @@
 void DevirtModule::applyVirtualConstProp(CallSiteInfo &CSInfo, StringRef FnName,
                                          Constant *Byte, Constant *Bit) {
   for (auto Call : CSInfo.CallSites) {
+    if (!OptimizedCalls.insert(&Call.CB).second)
+      continue;
     auto *RetType = cast<IntegerType>(Call.CB.getType());
     IRBuilder<> B(&Call.CB);
     Value *Addr =


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