[funcattrs] Consistently check call site attributes

This is mostly stylistic cleanup after D100226, but not entirely. When skimming the code, I found one case where we weren't accounting for attributes on the callsite at all. I'm also suspicious we had some latent bugs related to operand bundles (which are supposed to be able to *override* attributes on declarations), but I don't have concrete test cases for those, just suspicions.

Aside: The only case left in the file which directly checks attributes on the declaration is the norecurse logic. I left that because I didn't understand it; it looks obviously wrong, so I suspect I'm misinterpreting the intended semantics of the attribute.

Differential Revision: https://reviews.llvm.org/D100689

llvm/lib/Transforms/IPO/FunctionAttrs.cpp

@@ -1271,15 +1271,10 @@ static bool InstrBreaksNoFree(Instruction &I, const SCCNodeSet &SCCNodes) {
   if (CB->hasFnAttr(Attribute::NoFree))
     return false;
 
-  Function *Callee = CB->getCalledFunction();
-  if (!Callee)
-    return true;
-
-  if (Callee->doesNotFreeMemory())
-    return false;
-
-  if (SCCNodes.contains(Callee))
-    return false;
+  // Speculatively assume in SCC.
+  if (Function *Callee = CB->getCalledFunction())
+    if (SCCNodes.contains(Callee))
+      return false;
 
   return true;
 }
@@ -1403,10 +1398,8 @@ static bool addNoRecurseAttrs(const SCCNodeSet &SCCNodes) {
 }
 
 static bool instructionDoesNotReturn(Instruction &I) {
-  if (auto *CB = dyn_cast<CallBase>(&I)) {
-    Function *Callee = CB->getCalledFunction();
-    return Callee && Callee->doesNotReturn();
-  }
+  if (auto *CB = dyn_cast<CallBase>(&I))
+    return CB->hasFnAttr(Attribute::NoReturn);
   return false;
 }
 
@@ -1517,13 +1510,6 @@ static bool InstrBreaksNoSync(Instruction &I, const SCCNodeSet &SCCNodes) {
   if (CB->hasFnAttr(Attribute::NoSync))
     return false;
 
-  // readnone + not convergent implies nosync
-  // (This is needed to initialize inference from declarations which aren't
-  //  explicitly nosync, but are readnone and not convergent.)
-  if (CB->hasFnAttr(Attribute::ReadNone) &&
-      !CB->hasFnAttr(Attribute::Convergent))
-    return false;
-
   // Non volatile memset/memcpy/memmoves are nosync
   // NOTE: Only intrinsics with volatile flags should be handled here.  All
   // others should be marked in Intrinsics.td.

llvm/test/Transforms/FunctionAttrs/noreturn.ll

@@ -64,3 +64,10 @@ define i32 @caller6() naked {
 define i32 @alreadynoreturn() noreturn {
   unreachable
 }
+
+; CHECK: Function Attrs: {{.*}}noreturn
+; CHECK-NEXT: @callsite_noreturn()
+define void @callsite_noreturn() {
+  call i32 @f() noreturn
+  ret void
+}

llvm/test/Transforms/FunctionAttrs/willreturn-callsites.ll

@@ -1,4 +1,4 @@
-; RUN: opt -function-attrs -S %s | FileCheck %s
+; RUN: opt -inferattrs -function-attrs -S %s | FileCheck %s
 
 declare void @decl_readonly() readonly
 declare void @decl_readnone() readnone