Quick compiler: improve ClobberSReg comments
Issue 6501474
Improve the comments describing the usage of ClobberSReg(). Also, desk-checked all current
uses of ClobberSReg() to make sure they are appropriate.
No code changes - only comments.
Change-Id: Ife8419a7e2c2e51b258df7709a7d903d1fd93a44
diff --git a/src/compiler/codegen/ralloc_util.cc b/src/compiler/codegen/ralloc_util.cc
index 999c652..1a3a413 100644
--- a/src/compiler/codegen/ralloc_util.cc
+++ b/src/compiler/codegen/ralloc_util.cc
@@ -124,7 +124,17 @@
}
}
-/* Clobber any temp associated with an s_reg. Could be in either class */
+/*
+ * Break the association between a Dalvik vreg and a physical temp register of either register
+ * class.
+ * TODO: Ideally, the public version of this code should not exist. Besides its local usage
+ * in the register utilities, is is also used by code gen routines to work around a deficiency in
+ * local register allocation, which fails to distinguish between the "in" and "out" identities
+ * of Dalvik vregs. This can result in useless register copies when the same Dalvik vreg
+ * is used both as the source and destination register of an operation in which the type
+ * changes (for example: INT_TO_FLOAT v1, v1). Revisit when improved register allocation is
+ * addressed.
+ */
void ClobberSReg(CompilationUnit* cu, int s_reg)
{
#ifndef NDEBUG