commit 243db252574a78ff7326e7446d9042e321314c4f
author Ben Cheng <bccheng@android.com> Fri Apr 22 17:16:42 2011 -0700
committer buzbee <buzbee@google.com> Sat Apr 23 10:34:13 2011 -0700
tree 6a31b4b9a5dcee556b2a6b8767cf78a0ce642463
parent 0ed5b9bf184b97b0d3fa2ef5a9f3dacd3e186e46

Local optimization fixes for diverences found by self verification.

1) Only optimize each block once. Strictly speaking this is not a
correctness issue however it triggers the subsequent problem.

2) Ignore dead instructions.

    1: ldr     r2, [r5, #8]
    2: ldr     r3, [r5, #8](nop)
    3: str     r3, [r5, #4]
    4: movs    r3, r2

When using instruction 1 to initiate redundant ld/st eliminations, if
instruction 2 (which is already dead) is not ignored, it will be turned
into a "mov r3, r2" and that will clobber r3 used by the str.

Change-Id: I6b9a88d3688889d917b90f4b8f55278df1701c6a

vm/compiler/codegen/arm/CodegenDriver.cpp

diff --git a/vm/compiler/codegen/arm/CodegenDriver.cpp b/vm/compiler/codegen/arm/CodegenDriver.cpp
index a722289..d170c8b 100644
--- a/vm/compiler/codegen/arm/CodegenDriver.cpp
+++ b/vm/compiler/codegen/arm/CodegenDriver.cpp
@@ -4572,6 +4572,8 @@
              */
             dvmCompilerApplyLocalOptimizations(cUnit, (LIR *) headLIR,
                                                cUnit->lastLIRInsn);
+            /* Reset headLIR which is also the optimization boundary */
+            headLIR = NULL;
         }
 
 gen_fallthrough:

vm/compiler/codegen/arm/LocalOptimizations.cpp

diff --git a/vm/compiler/codegen/arm/LocalOptimizations.cpp b/vm/compiler/codegen/arm/LocalOptimizations.cpp
index 4c0354a..ffeaa57 100644
--- a/vm/compiler/codegen/arm/LocalOptimizations.cpp
+++ b/vm/compiler/codegen/arm/LocalOptimizations.cpp
@@ -131,6 +131,12 @@
              checkLIR != tailLIR;
              checkLIR = NEXT_LIR(checkLIR)) {
 
+            /*
+             * Skip already dead instructions (whose dataflow information is
+             * outdated and misleading).
+             */
+            if (checkLIR->flags.isNop) continue;
+
             u8 checkMemMask = (checkLIR->useMask | checkLIR->defMask) &
                               ENCODE_MEM;
             u8 aliasCondition = thisMemMask & checkMemMask;
@@ -312,6 +318,10 @@
              checkLIR != headLIR;
              checkLIR = PREV_LIR(checkLIR)) {
 
+            /*
+             * Skip already dead instructions (whose dataflow information is
+             * outdated and misleading).
+             */
             if (checkLIR->flags.isNop) continue;
 
             u8 checkMemMask = checkLIR->defMask & ENCODE_MEM;