[clang][CGStmt] fix crash on invalid asm statement

[ztong0001]

Summary

Clang is crashing on the following statement

char var[9];
__asm__ ("" : "=r" (var) : "0" (var));

This is similar to existing test: crbug_999160_regtest

The issue happens when EmitAsmStmt is trying to convert input to match
output type length. However, that is not guaranteed to be successful all the
time and if the statement itself is invalid like having an array type in
the example, we should give a regular error message here instead of
using assert().

[ztong0001]

reformat test code

[ztong0001]

reformat code

[MaskRay]

clang/lib/CodeGen/CGStmt.cpp

2517

Shall we keep the assert (in a new else branch) just in case there are other cases which cannot be handled?

[ztong0001]

clang/lib/CodeGen/CGStmt.cpp

2517

IMO adding assert() in else branch still has the same issue with the inline asm in description.

This portion of the code is to extend argument to a longer type, if it cannot do so the patch will simply skip and let it fall back to old behavior and print out

impossible constraint in asm: can't store value into a register

[MaskRay]

Thanks!

[ztong0001]

Hi Fangrui @MaskRay,
Thanks for your review. Could you please also help me landing it since I don't have write permission to the repo.
Please use Tong Zhang<[e-mail]>
Thanks and have a good one!

• Tong

[pengfei]

This comment was removed by pengfei.

clang/lib/CodeGen/CGStmt.cpp

if (Info.hasTiedOperand()) {
       QualType InputTy = InputExpr->getType();
 
       if (getContext().getTypeSize(OutputType) >
           getContext().getTypeSize(InputTy)) {
         // Use ptrtoint as appropriate so that we can do our extension.
         if (isa<llvm::PointerType>(Arg->getType()))
           Arg = Builder.CreatePtrToInt(Arg, IntPtrTy);
         llvm::Type *OutputTy = ConvertType(OutputType);
         if (isa<llvm::IntegerType>(OutputTy))
           Arg = Builder.CreateZExt(Arg, OutputTy);
         else if (isa<llvm::PointerType>(OutputTy))
           Arg = Builder.CreateZExt(Arg, IntPtrTy);
-        else {
-          assert(OutputTy->isFloatingPointTy() && "Unexpected output type");
+        else if (OutputTy->isFloatingPointTy())
           Arg = Builder.CreateFPExt(Arg, OutputTy);
-        }
-      }
       // Deal with the tied operands' constraint code in adjustInlineAsmType.
       ReplaceConstraint = OutputConstraints[Output];
     }
     if (llvm::Type* AdjTy =
           getTargetHooks().adjustInlineAsmType(*this, ReplaceConstraint,
                                                    Arg->getType()))
       Arg = Builder.CreateBitCast(Arg, AdjTy);
     else

clang/test/CodeGen/X86/x86_64-PR42672.c

 // RUN: %clang_cc1 -triple=x86_64-unknown-linux-gnu -DSTRUCT -emit-llvm %s -o - 2>&1 | FileCheck %s --check-prefix=CHECK-STRUCT
 // RUN: %clang_cc1 -triple=x86_64-unknown-linux-gnu -USTRUCT -emit-llvm %s -o - 2>&1 | FileCheck %s --check-prefix=CHECK-NOSTRUCT
 // RUN: not %clang_cc1 -triple=x86_64-unknown-linux-gnu -DIMPOSSIBLE_ODD -emit-llvm %s -o - 2>&1 | FileCheck %s --check-prefix=CHECK-IMPOSSIBLE_ODD
 // RUN: not %clang_cc1 -triple=x86_64-unknown-linux-gnu -DIMPOSSIBLE_BIG -emit-llvm %s -o - 2>&1 | FileCheck %s --check-prefix=CHECK-IMPOSSIBLE_BIG
 // RUN: %clang_cc1 -triple=x86_64-unknown-linux-gnu -DPOSSIBLE_X -emit-llvm %s -o - 2>&1 | FileCheck %s --check-prefix=CHECK-X
 // RUN: not %clang_cc1 -triple=x86_64-unknown-linux-gnu -DIMPOSSIBLE_X -emit-llvm %s -o - 2>&1 | FileCheck %s --check-prefix=CHECK-IMPOSSIBLE_X
 // RUN: not %clang_cc1 -triple=x86_64-unknown-linux-gnu -DIMPOSSIBLE_9BYTES -emit-llvm %s -o - 2>&1 | FileCheck %s --check-prefix=CHECK-IMPOSSIBLE_9BYTES
+// RUN: not %clang_cc1 -triple=x86_64-unknown-linux-gnu -DIMPOSSIBLE_9BYTES_V2 -emit-llvm %s -o - 2>&1 | FileCheck %s --check-prefix=CHECK-IMPOSSIBLE_9BYTES_V2
 
 // Make sure Clang doesn't treat |lockval| as asm input.
 void _raw_spin_lock(void) {
 #ifdef STRUCT
   struct {
     unsigned short owner, next;
   } lockval;
   lockval.owner = 1;

 #ifdef IMPOSSIBLE_9BYTES
   char buf[9];
   asm(""
       : "=r"(buf));
 #endif
 }
 
 // CHECK-IMPOSSIBLE_9BYTES: impossible constraint in asm: can't store value into a register
+
+void crbug_999160_regtest_v2(void) {
+#ifdef IMPOSSIBLE_9BYTES_V2
+  char buf[9];
+  asm("" : "=r"(buf) : "0"(buf));
+#endif
+}
+// CHECK-IMPOSSIBLE_9BYTES_V2: impossible constraint in asm: can't store value into a register