Handle putchar (rust-lang#241)

Author: wsmoses

enzyme/Enzyme/ActivityAnalysis.cpp

@@ -87,6 +87,7 @@ std::set<std::string> KnownInactiveFunctions = {
     "__cxa_guard_release",
     "__cxa_guard_abort",
     "printf",
+    "putchar",
     "vprintf",
     "puts",
     "fflush",

enzyme/test/Enzyme/ReverseMode/putchar.ll

@@ -0,0 +1,30 @@
+; RUN: %opt < %s %loadEnzyme -enzyme -enzyme-preopt=false -O3 -S | FileCheck %s
+
+declare i32 @putchar(i32) 
+
+; Function Attrs: nounwind readnone uwtable
+define double @tester(double %x) {
+entry:
+  %tmp = call i32 @putchar(i32 32)
+  %0 = tail call fast double @llvm.exp.f64(double %x)
+  ret double %0
+}
+
+define double @test_derivative(double %x) {
+entry:
+  %0 = tail call double (double (double)*, ...) @__enzyme_autodiff(double (double)* nonnull @tester, double %x)
+  ret double %0
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare double @llvm.exp.f64(double)
+
+; Function Attrs: nounwind
+declare double @__enzyme_autodiff(double (double)*, ...)
+
+; CHECK: define double @test_derivative(double %x)
+; CHECK-NEXT: entry:
+; CHECK-NEXT:   %tmp.i = tail call i32 @putchar(i32 32)
+; CHECK-NEXT:   %0 = tail call fast double @llvm.exp.f64(double %x)
+; CHECK-NEXT:   ret double %0
+; CHECK-NEXT: }