[PATCH] D146267: [llvm] Handle duplicate call bases when applying branch funneling

[Leonard Chan via Phabricator via llvm-commits]

leonardchan updated this revision to Diff 507179.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D146267/new/

https://reviews.llvm.org/D146267

Files:
  llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
  llvm/test/Transforms/WholeProgramDevirt/branch-funnel.ll


Index: llvm/test/Transforms/WholeProgramDevirt/branch-funnel.ll
===================================================================
--- llvm/test/Transforms/WholeProgramDevirt/branch-funnel.ll
+++ llvm/test/Transforms/WholeProgramDevirt/branch-funnel.ll
@@ -233,6 +233,54 @@
   ret i32 %result
 }
 
+; CHECK-LABEL: define i32 @fn4
+; CHECK-NOT: call void (...) @llvm.icall.branch.funnel
+define i32 @fn4(ptr %obj) #0 {
+  %p = call i1 @llvm.type.test(ptr @vt1_1, metadata !"typeid1")
+  call void @llvm.assume(i1 %p)
+  %fptr = load ptr, ptr @vt1_1
+  ; RETP: call i32 @__typeid_typeid1_0_branch_funnel(ptr nest @vt1_1, ptr %obj, i32 1)
+  %result = call i32 %fptr(ptr %obj, i32 1)
+  ; NORETP: call i32 %
+  ret i32 %result
+}
+
+; CHECK-LABEL: define i32 @fn4_cpy
+; CHECK-NOT: call void (...) @llvm.icall.branch.funnel
+define i32 @fn4_cpy(ptr %obj) #0 {
+  %p = call i1 @llvm.type.test(ptr @vt1_1, metadata !"typeid1")
+  call void @llvm.assume(i1 %p)
+  %fptr = load ptr, ptr @vt1_1
+  ; RETP: call i32 @__typeid_typeid1_0_branch_funnel(ptr nest @vt1_1, ptr %obj, i32 1)
+  %result = call i32 %fptr(ptr %obj, i32 1)
+  ; NORETP: call i32 %
+  ret i32 %result
+}
+
+; CHECK-LABEL: define i32 @fn4_rv
+; CHECK-NOT: call void (...) @llvm.icall.branch.funnel
+define i32 @fn4_rv(ptr %obj) #0 {
+  %p = call i1 @llvm.type.test(ptr @vt1_1_rv, metadata !"typeid1_rv")
+  call void @llvm.assume(i1 %p)
+  %fptr = call ptr @llvm.load.relative.i32(ptr @vt1_1_rv, i32 0)
+  ; RETP: call i32 @__typeid_typeid1_rv_0_branch_funnel(ptr nest @vt1_1_rv, ptr %obj, i32 1)
+  %result = call i32 %fptr(ptr %obj, i32 1)
+  ; NORETP: call i32 %
+  ret i32 %result
+}
+
+; CHECK-LABEL: define i32 @fn4_rv_cpy
+; CHECK-NOT: call void (...) @llvm.icall.branch.funnel
+define i32 @fn4_rv_cpy(ptr %obj) #0 {
+  %p = call i1 @llvm.type.test(ptr @vt1_1_rv, metadata !"typeid1_rv")
+  call void @llvm.assume(i1 %p)
+  %fptr = call ptr @llvm.load.relative.i32(ptr @vt1_1_rv, i32 0)
+  ; RETP: call i32 @__typeid_typeid1_rv_0_branch_funnel(ptr nest @vt1_1_rv, ptr %obj, i32 1)
+  %result = call i32 %fptr(ptr %obj, i32 1)
+  ; NORETP: call i32 %
+  ret i32 %result
+}
+
 ; CHECK-LABEL: define hidden void @__typeid_typeid1_0_branch_funnel(ptr nest %0, ...)
 ; CHECK-NEXT: musttail call void (...) @llvm.icall.branch.funnel(ptr %0, ptr {{(nonnull )?}}@vt1_1, ptr {{(nonnull )?}}@vf1_1, ptr {{(nonnull )?}}@vt1_2, ptr {{(nonnull )?}}@vf1_2, ...)
 
Index: llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
===================================================================
--- llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
+++ llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
@@ -1391,9 +1391,24 @@
       IsExported = true;
     if (CSInfo.AllCallSitesDevirted)
       return;
+
+    SmallPtrSet<CallBase *, 8> CallBases;
     for (auto &&VCallSite : CSInfo.CallSites) {
       CallBase &CB = VCallSite.CB;
 
+      if (CallBases.contains(&CB)) {
+        // When finding devirtualizable calls, it's possible to find the same
+        // vtable passed to multiple llvm.type.test or llvm.type.checked.load
+        // calls, which can cause duplicate call sites to be recorded in
+        // [Const]CallSites. If we've already replaced and erased one of these
+        // call instances, just ignore it.
+        //
+        // All other areas in WPD which iterate over the CallSites account for
+        // duplicate call bases add them to a set to mark them as devirtualized
+        // and skip over them if they're already in the set.
+        continue;
+      }
+
       // Jump tables are only profitable if the retpoline mitigation is enabled.
       Attribute FSAttr = CB.getCaller()->getFnAttribute("target-features");
       if (!FSAttr.isValid() ||
@@ -1440,6 +1455,7 @@
           AttributeList::get(M.getContext(), Attrs.getFnAttrs(),
                              Attrs.getRetAttrs(), NewArgAttrs));
 
+      CallBases.insert(&CB);
       CB.replaceAllUsesWith(NewCS);
       CB.eraseFromParent();
 


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