[FuncSpec] Don't specialise call sites that have the MinSize attribute set

The MinSize attribute can be attached to both the callee and the caller
in the callsite. Function specialisation was already skipped for function
declarations (callees) with MinSize. This also skips specialisations for
the callsite when it has MinSize set.

Differential Revision: https://reviews.llvm.org/D109441

llvm/lib/Transforms/IPO/FunctionSpecialization.cpp

@@ -659,6 +659,12 @@ private:
       if (!isa<CallInst>(U) && !isa<InvokeInst>(U))
         continue;
       auto &CS = *cast<CallBase>(U);
+      // If the call site has attribute minsize set, that callsite won't be
+      // specialized.
+      if (CS.hasFnAttr(Attribute::MinSize)) {
+        AllConstant = false;
+        continue;
+      }
 
       // If the parent of the call site will never be executed, we don't need
       // to worry about the passed value.
@@ -688,6 +694,9 @@ private:
   /// This function modifies calls to function \p F whose argument at index \p
   /// ArgNo is equal to constant \p C. The calls are rewritten to call function
   /// \p Clone instead.
+  ///
+  /// Callsites that have been marked with the MinSize function attribute won't
+  /// be specialized and rewritten.
   void rewriteCallSites(Function *F, Function *Clone, Argument &Arg,
                         Constant *C) {
     unsigned ArgNo = Arg.getArgNo();

llvm/test/Transforms/FunctionSpecialization/function-specialization-minsize2.ll

@@ -0,0 +1,44 @@
+; RUN: opt -function-specialization -func-specialization-size-threshold=3 -S < %s | FileCheck %s
+
+; Checks for callsites that have been annotated with MinSize. No specialisation
+; expected here:
+;
+; CHECK-NOT: @compute.1
+; CHECK-NOT: @compute.2
+
+define i64 @main(i64 %x, i1 %flag) {
+entry:
+  br i1 %flag, label %plus, label %minus
+
+plus:
+  %tmp0 = call i64 @compute(i64 %x, i64 (i64)* @plus) #0
+  br label %merge
+
+minus:
+  %tmp1 = call i64 @compute(i64 %x, i64 (i64)* @minus) #0
+  br label %merge
+
+merge:
+  %tmp2 = phi i64 [ %tmp0, %plus ], [ %tmp1, %minus]
+  ret i64 %tmp2
+}
+
+define internal i64 @compute(i64 %x, i64 (i64)* %binop) {
+entry:
+  %tmp0 = call i64 %binop(i64 %x)
+  ret i64 %tmp0
+}
+
+define internal i64 @plus(i64 %x) {
+entry:
+  %tmp0 = add i64 %x, 1
+  ret i64 %tmp0
+}
+
+define internal i64 @minus(i64 %x) {
+entry:
+  %tmp0 = sub i64 %x, 1
+  ret i64 %tmp0
+}
+
+attributes #0 = { minsize optsize }

llvm/test/Transforms/FunctionSpecialization/function-specialization-minsize3.ll

@@ -0,0 +1,48 @@
+; RUN: opt -function-specialization -func-specialization-size-threshold=3 -S < %s | FileCheck %s
+
+; Checks for callsites that have been annotated with MinSize. We only expect
+; specialisation for the call that does not have the attribute:
+;
+; CHECK: plus:
+; CHECK:   %tmp0 = call i64 @compute.1(i64 %x, i64 (i64)* @plus)
+; CHECK:   br label %merge
+; CHECK: minus:
+; CHECK:   %tmp1 = call i64 @compute(i64 %x, i64 (i64)* @minus) #0
+; CHECK:   br label %merge
+;
+define i64 @main(i64 %x, i1 %flag) {
+entry:
+  br i1 %flag, label %plus, label %minus
+
+plus:
+  %tmp0 = call i64 @compute(i64 %x, i64 (i64)* @plus)
+  br label %merge
+
+minus:
+  %tmp1 = call i64 @compute(i64 %x, i64 (i64)* @minus) #0
+  br label %merge
+
+merge:
+  %tmp2 = phi i64 [ %tmp0, %plus ], [ %tmp1, %minus]
+  ret i64 %tmp2
+}
+
+define internal i64 @compute(i64 %x, i64 (i64)* %binop) {
+entry:
+  %tmp0 = call i64 %binop(i64 %x)
+  ret i64 %tmp0
+}
+
+define internal i64 @plus(i64 %x) {
+entry:
+  %tmp0 = add i64 %x, 1
+  ret i64 %tmp0
+}
+
+define internal i64 @minus(i64 %x) {
+entry:
+  %tmp0 = sub i64 %x, 1
+  ret i64 %tmp0
+}
+
+attributes #0 = { minsize optsize }