Latest version of the patch is attached which fixes a couple of oversights. I had to add a line which checks whether Ty is a dependent type before getTypeSize is called. Also, in the test case, "=" was missing before constraint "a", so fixed that too.

On Wed, Aug 27, 2014 at 3:22 PM, Reid Kleckner <[email protected]> wrote:
New patch looks good to me.

It sounds like we have two cases of size mismatch:
- The output operand lvalue is smaller than the constraint, meaning the store will write out of bounds. Your patch adds this.
- The output operand lvalue is bigger than the constraint, meaning the whole value won't be initialized. We currently warn here via validateConstraintModifier.

This code probably deserves some cleanup, but your patch is consistent with what we do for input operands, so let's go with that.


The reason llvm is crashing in the backend is that it's trying to use a 64-bit register in 32-bit mode. It's not because a store is writing out of bounds or there is a value left uninitialized. In the test case, if we declare the variable bound to constraint "=a" to be a unit32_t or an integer type that is smaller than 32-bit, clang compiles the program fine.
  

On Wed, Aug 27, 2014 at 12:35 PM, Akira Hatanaka <[email protected]> wrote:
The commit log in r166737 doesn't say much about why this is a warning instead of an error, but I know there are cases where warnings are needed. For example, clang has to issue warnings instead of errors for the inline-asm statements in the test case committed in r216260. If it's not desirable to change validateConstraintModifier, we can add a function which checks the output size that is similar to validateInputSize in r167717 (see attached patch), which was suggested in the post-commit review.


I am not sure whether we can use fixit in this case. Fixit hints should be used only if we know the user's intent and it's very clear that applying the fixit hint is the right thing to do. Changing the type of variable "r" to a 32-bit int will avoid crashing, but it doesn't look like that's what the user wants.

On Mon, Aug 25, 2014 at 6:20 PM, Reid Kleckner <[email protected]> wrote:
Can you investigate why we are warning in the first place? I think we should either only warn or only error. Currently we have a warning with a fixit but we don't recover as though we had applied the fixit. If we did that, we would not crash.

In addition to the Clang-side changes, LLVM should probably be returning an error or reporting a fatal error instead of hitting unreachable.


On Mon, Aug 25, 2014 at 2:10 PM, Akira Hatanaka <[email protected]> wrote:
Rebased patches attached.

I also made changes to the clang patch so that clang can error-out after a size mismatch is found as soon as possible.TargetInfo::validateConstraintModifier has an extra parameter IsError, which is set when it decides there is no point in continuing compilation and it should stop compilation immediately. The error message clang prints looks better than lllvm's message, but if it isn't right to change the warning to an error, then I guess we have to detect the error later just before isel, as is done in the llvm patch.

On Wed, Jul 23, 2014 at 3:56 PM, Akira Hatanaka <[email protected]> wrote:
llvm should error-out when a 64-bit variable is bound to a single register in x86 32-bit mode, but ToT clang/llvm fails to detect this error and continues compilation until it crashes in type-legalization:

$ llc test/CodeGen/X86/inline-asm-regsize.ll  -O3 -mtriple=i386-apple-darwin -o -


inline-asm-regsize.ll  -O3 -mtriple=i386-apple-darwin -o -

.section __TEXT,__text,regular,pure_instructions

ExpandIntegerResult #0: 0x7fa2d1041728: i64 = Register %RCX [ID=0]


Do not know how to expand the result of this operator!

UNREACHABLE executed at /Users/ahatanaka/projects/llvm/git/llvm3/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp:1116!


The attached patch fixes llvm to error-out and print this error message:

error: Cannot bind a variable larger than 32-bit to a single register in 32-bit mode


My initial solution was to have clang detect this error in TargetInfo::validateConstraintModifier. However, the code in SemaStmtAsm.cpp has to be changed to error-out instead of issuing a warning, which I wasn't sure was the right thing to do. I am attaching this patch too in case someone has a suggestion or an opinion on it.




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diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 6f96e3a..314e020 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6030,6 +6030,8 @@ let CategoryName = "Inline Assembly Issue" in {
   def err_asm_bad_register_type : Error<"bad type for named register variable">;
   def err_asm_invalid_input_size : Error<
     "invalid input size for constraint '%0'">;
+  def err_asm_invalid_output_size : Error<
+    "invalid output size for constraint '%0'">;
   def err_invalid_asm_cast_lvalue : Error<
     "invalid use of a cast in a inline asm context requiring an l-value: "
     "remove the cast or build with -fheinous-gnu-extensions">;
diff --git a/include/clang/Basic/TargetInfo.h b/include/clang/Basic/TargetInfo.h
index e26f595..511b6f0 100644
--- a/include/clang/Basic/TargetInfo.h
+++ b/include/clang/Basic/TargetInfo.h
@@ -577,6 +577,10 @@ public:
   bool validateInputConstraint(ConstraintInfo *OutputConstraints,
                                unsigned NumOutputs,
                                ConstraintInfo &info) const;
+  virtual bool validateOutputSize(StringRef /*Constraint*/,
+                                  unsigned /*Size*/) const {
+    return true;
+  }
   virtual bool validateInputSize(StringRef /*Constraint*/,
                                  unsigned /*Size*/) const {
     return true;
diff --git a/lib/Basic/Targets.cpp b/lib/Basic/Targets.cpp
index 4998ca3..add0c2d 100644
--- a/lib/Basic/Targets.cpp
+++ b/lib/Basic/Targets.cpp
@@ -3105,14 +3105,33 @@ public:
     if (RegNo == 1) return 2;
     return -1;
   }
+
+  bool validateOutputSize(StringRef Constraint,
+                         unsigned Size) const override {
+    // Strip off constraint modifiers.
+    while (Constraint[0] == '=' ||
+           Constraint[0] == '+' ||
+           Constraint[0] == '&')
+      Constraint = Constraint.substr(1);
+
+    return validateOperandSize(Constraint, Size);
+  }
+
   bool validateInputSize(StringRef Constraint,
                          unsigned Size) const override {
+    return validateOperandSize(Constraint, Size);
+  }
+
+  bool validateOperandSize(StringRef Constraint,
+                           unsigned Size) const {
     switch (Constraint[0]) {
     default: break;
     case 'a':
     case 'b':
     case 'c':
     case 'd':
+    case 'S':
+    case 'D':
       return Size <= 32;
     }
 
diff --git a/lib/Sema/SemaStmtAsm.cpp b/lib/Sema/SemaStmtAsm.cpp
index 47a7672..f1f7f54 100644
--- a/lib/Sema/SemaStmtAsm.cpp
+++ b/lib/Sema/SemaStmtAsm.cpp
@@ -121,6 +121,18 @@ StmtResult Sema::ActOnGCCAsmStmt(SourceLocation AsmLoc, bool IsSimple,
       return StmtError();
 
     OutputConstraintInfos.push_back(Info);
+
+    const Type *Ty = OutputExpr->getType().getTypePtr();
+
+    if (Ty->isDependentType())
+      continue;
+
+    unsigned Size = Context.getTypeSize(Ty);
+    if (!Context.getTargetInfo().validateOutputSize(Literal->getString(),
+                                                    Size))
+      return StmtError(Diag(OutputExpr->getLocStart(),
+                            diag::err_asm_invalid_output_size)
+                       << Info.getConstraintStr());
   }
 
   SmallVector<TargetInfo::ConstraintInfo, 4> InputConstraintInfos;
diff --git a/test/CodeGen/x86_32-inline-asm.c b/test/CodeGen/x86_32-inline-asm.c
index 473f78e..16dcad3 100644
--- a/test/CodeGen/x86_32-inline-asm.c
+++ b/test/CodeGen/x86_32-inline-asm.c
@@ -17,8 +17,13 @@ int func1() {
                      "a" ((val & 0xFFFFFFFFUL)), // expected-error {{invalid input size for constraint 'a'}}
                      "d" (((val >> 32) & 0xFFFFFFFFUL)));
 
+  __asm__ volatile("addl %1, %0" : "=a" (msr) : "S" (val)); // expected-error {{invalid input size for constraint 'S'}}
+
   // Don't error out if the size of the destination is <= 32 bits.
   unsigned char data;
   unsigned int port;
   __asm__ volatile("outb %0, %w1" : : "a" (data), "Nd" (port)); // No error expected.
+
+  // Error out if a 64-bit variable is bound to a single register.
+  __asm__ volatile("addl %1, %0" : "=a" (val) : "a" (msr)); // expected-error {{invalid output size for constraint '=a'}}
 }
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