llvm-reduce: Preserve original callsite calling conv when removing arguments

In undefined mismatch cases, this was fixing the callsite to use the calling
convention of the new function. Preserve the original wrong callsite's calling
convention.

Author: arsenm

llvm/test/tools/llvm-reduce/remove-arguments-preserve-wrong-cc.ll

@@ -0,0 +1,27 @@
+; Check that when removing arguments, incorrect callsite calling conventions are preserved
+
+; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=arguments --test FileCheck --test-arg --check-prefixes=INTERESTING --test-arg %s --test-arg --input-file %s -o %t
+; RUN: FileCheck --check-prefixes=RESULT %s < %t
+
+; INTERESTING-LABEL: @fastcc_callee(
+define fastcc i32 @fastcc_callee(i32 %a, i32 %b) {
+  ret i32 %a
+}
+
+; INTERESTING-LABEL: @fastcc_callee_decl(
+declare fastcc i32 @fastcc_callee_decl(i32 %a, i32 %b)
+
+; INTERESTING-LABEL: @caller_wrong_callsites(
+; INTERESTING: call
+; INTERESTING: call
+
+; RESULT-LABEL: define i32 @caller_wrong_callsites()
+; RESULT: %call0 = call coldcc i32 @fastcc_callee()
+; RESULT: %call1 = call i32 @fastcc_callee_decl()
+define i32 @caller_wrong_callsites(i32 %x) {
+  %call0 = call coldcc i32 @fastcc_callee(i32 %x, i32 2)
+  %call1 = call ccc i32 @fastcc_callee_decl(i32 %x, i32 2)
+  %result = add i32 %call0, %call1
+  ret i32 %result
+}
+

llvm/tools/llvm-reduce/deltas/ReduceArguments.cpp

@@ -65,7 +65,7 @@ static void replaceFunctionCalls(Function &OldF, Function &NewF,
       CI->getOperandBundlesAsDefs(OpBundles);
 
       CallInst *NewCI = CallInst::Create(&NewF, Args, OpBundles);
-      NewCI->setCallingConv(NewF.getCallingConv());
+      NewCI->setCallingConv(CI->getCallingConv());
 
       AttrBuilder CallSiteAttrs(Ctx, CI->getAttributes().getFnAttrs());
       NewCI->setAttributes(