Win64 ABI shouldn't extend integer type arguments.

Summary:
MSVC doesn't extend integer types smaller than 64bit, so to preserve
binary compatibility, clang shouldn't either.

For example, the following C code built with MSVC:

unsigned test(unsigned v);
unsigned foobar(unsigned short);
int main() { return test(0xffffffff) + foobar(28); }

Produces the following:

  0000000000000004: B9 FF FF FF FF     mov         ecx,0FFFFFFFFh
  0000000000000009: E8 00 00 00 00     call        test
  000000000000000E: 89 44 24 20        mov         dword ptr [rsp+20h],eax
  0000000000000012: 66 B9 1C 00        mov         cx,1Ch
  0000000000000016: E8 00 00 00 00     call        foobar

And as you can see, when setting up the call to foobar, only cx is overwritten.

If foobar is compiled with clang, then the zero extension added by clang means
the rest of the register, which contains garbage, could be used.

For example if foobar is:

unsigned foobar(unsigned short v) {
    return v;
}

Compiled with clang -fomit-frame-pointer -O3 gives the following assembly:

foobar:
  0000000000000000: 89 C8              mov         eax,ecx
  0000000000000002: C3                 ret

And that function would return garbage because the 16 most significant bits of
ecx still contain garbage from the first call.

With this change, the code for that function is now:

foobar:
  0000000000000000: 0F B7 C1           movzx       eax,cx
  0000000000000003: C3                 ret

Reviewers: chapuni, rnk

Reviewed By: rnk

Subscribers: majnemer, cfe-commits

Differential Revision: http://reviews.llvm.org/D4380

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@216491 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/TargetInfo.cpp b/lib/CodeGen/TargetInfo.cpp
index ea5f7c22399c48c6135e5f55548b8598d3bb582e..4e4f03b6c0999c8c8c8fcc3bfba0d47b28b489a7 100644 (file)
--- a/lib/CodeGen/TargetInfo.cpp
+++ b/lib/CodeGen/TargetInfo.cpp
@@ -2773,9 +2773,6 @@ ABIArgInfo WinX86_64ABIInfo::classify(QualType Ty, bool IsReturnType) const {
     return ABIArgInfo::getDirect(llvm::IntegerType::get(getVMContext(), Size));
   }
 
-  if (Ty->isPromotableIntegerType())
-    return ABIArgInfo::getExtend();
-
   return ABIArgInfo::getDirect();
 }
 

diff --git a/test/CodeGen/2007-06-18-SextAttrAggregate.c b/test/CodeGen/2007-06-18-SextAttrAggregate.c
index 92171e2bd9b7852d5f7ceaf91bbb17ee0230f2e9..22aa95a6bff96c444bde4db66f936e3088a2ac56 100644 (file)
--- a/test/CodeGen/2007-06-18-SextAttrAggregate.c
+++ b/test/CodeGen/2007-06-18-SextAttrAggregate.c
@@ -1,11 +1,13 @@
 // RUN: %clang_cc1 %s -o - -emit-llvm | FileCheck %s
-// XFAIL: aarch64, arm64
+// XFAIL: aarch64, arm64, x86_64-pc-win32
 
 // PR1513
 
 // AArch64 ABI actually requires the reverse of what this is testing: the callee
 // does any extensions and remaining bits are unspecified.
 
+// Win64 ABI does expect extensions for type smaller than 64bits.
+
 // Technically this test wasn't written to test that feature, but it's a
 // valuable check nevertheless.
 

diff --git a/test/CodeGen/x86_64-arguments-win32.c b/test/CodeGen/x86_64-arguments-win32.c
new file mode 100644 (file)
index 0000000..5aea7fc
--- /dev/null
+++ b/test/CodeGen/x86_64-arguments-win32.c
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -w -triple x86_64-pc-win32 -emit-llvm -o - %s | FileCheck %s
+
+// To be ABI compatible with code generated by MSVC, there shouldn't be any
+// sign/zero extensions on types smaller than 64bit.
+
+// CHECK-LABEL: define void @f1(i8 %a)
+void f1(char a) {}
+
+// CHECK-LABEL: define void @f2(i8 %a)
+void f2(unsigned char a) {}
+
+// CHECK-LABEL: define void @f3(i16 %a)
+void f3(short a) {}
+
+// CHECK-LABEL: define void @f4(i16 %a)
+void f4(unsigned short a) {}