[CaptureTracking] Take non-willreturn calls into account

We can leak one bit of information about the address by either
diverging or not.

Part of #129090.

Author: nikic

llvm/lib/Analysis/CaptureTracking.cpp

@@ -279,9 +279,9 @@ UseCaptureInfo llvm::DetermineUseCaptureKind(
   case Instruction::Invoke: {
     auto *Call = cast<CallBase>(I);
     // Not captured if the callee is readonly, doesn't return a copy through
-    // its return value and doesn't unwind (a readonly function can leak bits
-    // by throwing an exception or not depending on the input value).
-    if (Call->onlyReadsMemory() && Call->doesNotThrow() &&
+    // its return value and doesn't unwind or diverge (a readonly function can
+    // leak bits by throwing an exception or not depending on the input value).
+    if (Call->onlyReadsMemory() && Call->doesNotThrow() && Call->willReturn() &&
         Call->getType()->isVoidTy())
       return CaptureComponents::None;
 

llvm/test/Transforms/Attributor/nocapture-1.ll

@@ -337,9 +337,9 @@ define void @nc4(ptr %p) {
   ret void
 }
 
-define void @nc5(ptr %f, ptr %p) {
-; CHECK-LABEL: define {{[^@]+}}@nc5
-; CHECK-SAME: (ptr nofree noundef nonnull captures(none) [[F:%.*]], ptr captures(none) [[P:%.*]]) {
+define void @callsite_readonly_nounwind_not_willreturn(ptr %f, ptr %p) {
+; CHECK-LABEL: define {{[^@]+}}@callsite_readonly_nounwind_not_willreturn
+; CHECK-SAME: (ptr nofree noundef nonnull captures(none) [[F:%.*]], ptr [[P:%.*]]) {
 ; CHECK-NEXT:    call void [[F]](ptr captures(none) [[P]])
 ; CHECK-NEXT:    ret void
 ;
@@ -348,6 +348,17 @@ define void @nc5(ptr %f, ptr %p) {
   ret void
 }
 
+define void @callsite_readonly_nounwind_willreturn(ptr %f, ptr %p) {
+; CHECK-LABEL: define {{[^@]+}}@callsite_readonly_nounwind_willreturn
+; CHECK-SAME: (ptr nofree noundef nonnull captures(none) [[F:%.*]], ptr captures(none) [[P:%.*]]) {
+; CHECK-NEXT:    call void [[F]](ptr captures(none) [[P]])
+; CHECK-NEXT:    ret void
+;
+  call void %f(ptr %p) readonly nounwind willreturn
+  call void %f(ptr nocapture %p)
+  ret void
+}
+
 ; It would be acceptable to add readnone to %y1_1 and %y1_2.
 define void @test1_1(ptr %x1_1, ptr %y1_1, i1 %c) {
 ; TUNIT: Function Attrs: nofree nosync nounwind memory(write)