The attached patch allows inline assembly to inherit the readnone/readonly
function attribute from the caller. This allows the attributes to be retained
after function inlining. In turn, CSE is able to do it's magic on inline
assembly statements.
An orthogonal solution would be to add support for the const keyword for inline
assembly (e.g., asm const("mov $0x12345678, %0" : "=r" (ptr)); ).
Chad
Index: test/CodeGen/inline-asm-attr.c
===================================================================
--- test/CodeGen/inline-asm-attr.c (revision 0)
+++ test/CodeGen/inline-asm-attr.c (revision 0)
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -O3 -emit-llvm %s -o - |
FileCheck %s
+
+__attribute__((const))
+static inline void **varptr(void) {
+ void *ptr;
+ asm("mov $0x12345678, %0" : "=r" (ptr));
+ return ptr;
+}
+static inline void *getvar(void) { return *varptr(); }
+static inline void setvar(void *value) { *varptr() = value; }
+
+void fn(void) {
+// CHECK: @fn
+// CHECK: entry
+// CHECK: tail call i8* asm
+// CHECK: if.then
+// CHECK-NOT: tail call i8* asm
+// CHECK-NOT: far from pukin
+ if (getvar())
+ setvar(0);
+}
Index: lib/CodeGen/CGStmt.cpp
===================================================================
--- lib/CodeGen/CGStmt.cpp (revision 155999)
+++ lib/CodeGen/CGStmt.cpp (working copy)
@@ -1633,6 +1633,13 @@
S.isVolatile() || S.getNumOutputs() == 0);
llvm::CallInst *Result = Builder.CreateCall(IA, Args);
Result->addAttribute(~0, llvm::Attribute::NoUnwind);
+
+ // Allow the inline assembly to inherit the ReadNone/ReadOnly attribute.
+ llvm::Function *Fn = Result->getParent()->getParent();
+ if (Fn->hasFnAttr(llvm::Attribute::ReadNone))
+ Result->addAttribute(~0, llvm::Attribute::ReadNone);
+ if (Fn->hasFnAttr(llvm::Attribute::ReadOnly))
+ Result->addAttribute(~0, llvm::Attribute::ReadOnly);
// Slap the source location of the inline asm into a !srcloc metadata on the
// call.
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