[InstCombine] Special handle va_copy(dst, src) + va_end(src)

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -816,9 +816,12 @@ removeTriviallyEmptyRange(IntrinsicInst &EndI, InstCombinerImpl &IC,
 }
 
 Instruction *InstCombinerImpl::visitVAEndInst(VAEndInst &I) {
-  removeTriviallyEmptyRange(I, *this, [](const IntrinsicInst &I) {
-    return I.getIntrinsicID() == Intrinsic::vastart ||
-           I.getIntrinsicID() == Intrinsic::vacopy;
+  removeTriviallyEmptyRange(I, *this, [&I](const IntrinsicInst &II) {
+    // Bail out on the case where the source va_list of a va_copy is destroyed
+    // immediately by a follow-up va_end.
+    return II.getIntrinsicID() == Intrinsic::vastart ||
+           (II.getIntrinsicID() == Intrinsic::vacopy &&
+            I.getArgOperand(0) != II.getArgOperand(1));
   });
   return nullptr;
 }

llvm/test/Transforms/InstCombine/vararg.ll

@@ -33,7 +33,9 @@ define void @func_destroy_copy_src(ptr nocapture readnone %fmt, ...) {
 ; CHECK-NEXT:    [[VA1:%.*]] = alloca [[STRUCT___VA_LIST]], align 8
 ; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 32, ptr nonnull [[VA0]])
 ; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 32, ptr nonnull [[VA1]])
+; CHECK-NEXT:    call void @llvm.va_start.p0(ptr nonnull [[VA0]])
 ; CHECK-NEXT:    call void @llvm.va_copy.p0(ptr nonnull [[VA1]], ptr nonnull [[VA0]])
+; CHECK-NEXT:    call void @llvm.va_end.p0(ptr [[VA0]])
 ; CHECK-NEXT:    call void @callee(ptr nonnull [[VA1]])
 ; CHECK-NEXT:    call void @llvm.va_end.p0(ptr [[VA1]])
 ; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 32, ptr nonnull [[VA1]])