[PATCH 3/5] MdePkg/BaseSynchronizationLib GCC: fix InternalSyncCompareExchange32()

[Laszlo Ersek <lersek@redhat.com>]

(This patch is identical to the last one, except for the
InternalSyncCompareExchange16() -> InternalSyncCompareExchange32() and
"cmpxchgw" -> "cmpxchgl" replacements.)

The CMPXCHG instruction has the following operands:
- AX (implicit, CompareValue):    input and output
- destination operand (*Value):   input and output
- source operand (ExchangeValue): input

The IA32 version of InternalSyncCompareExchange32() correctly marks
CompareValue as input/output, but it marks (*Value) only as input.

The X64 version of InternalSyncCompareExchange32() attempts to mark both
CompareValue and (*Value) as input/output, but it doesn't use the
appropriate constraints for either operand.

Fix these issues. Furthermore, prefer the short "+" constraint for I/O
operands over the <output-operand-number> constraint that can be applied
to the input instances of I/O operands.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1208
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c |  9 ++++-----
 MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c  | 10 ++++------
 2 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c b/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c
index bd98a5aebfe7..44188e265af2 100644
--- a/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c
+++ b/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c
@@ -155,11 +155,10 @@ InternalSyncCompareExchange32 (
 {
   __asm__ __volatile__ (
     "lock                 \n\t"
-    "cmpxchgl    %1, %2   \n\t"
-    : "=a" (CompareValue)       // %0
-    : "q"  (ExchangeValue),     // %1
-      "m"  (*Value),            // %2
-      "0"  (CompareValue)       // %3
+    "cmpxchgl    %2, %1   \n\t"
+    : "+a" (CompareValue),      // %0
+      "+m" (*Value)             // %1
+    : "q"  (ExchangeValue)      // %2
     : "memory",
       "cc"
     );
diff --git a/MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c b/MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c
index 4338fb8e65e8..a85cf0265c8b 100644
--- a/MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c
+++ b/MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c
@@ -155,12 +155,10 @@ InternalSyncCompareExchange32 (
 {
   __asm__ __volatile__ (
     "lock                 \n\t"
-    "cmpxchgl    %3, %1   \n\t"
-    : "=a" (CompareValue),      // %0
-      "=m" (*Value)             // %1
-    : "a"  (CompareValue),      // %2
-      "r"  (ExchangeValue),     // %3
-      "m"  (*Value)             // %4
+    "cmpxchgl    %2, %1   \n\t"
+    : "+a" (CompareValue),      // %0
+      "+m" (*Value)             // %1
+    : "r"  (ExchangeValue)      // %2
     : "memory",
       "cc"
     );
-- 
2.14.1.3.gb7cf6e02401b