llvm-reduce: Preserve original callsite calling conv when removing arguments (#133411)

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(