JIT: Reworked the assembler to be smarter about short instruction forms

Previously, the JIT wasn't generating short-form compare and branch on
zero/not zero instructions for Thumb2.  The reason was that these only
allow a 1-byte displacement, and when they didn't reach the assembler would
abort the trace, split it in half and try again.  This change re-enables
cbz, cbnz generation and introduces a relatively lightweight retry
mechanism.

Also includes changes for Thumb2 to always generate large displacement
literal loads and conditional branches to minimize the number of retry
attempts.

Change-Id: Icf066836fad203f5c0fcbbb2ae8e1aa73d1cf816

1 files changed, 8 insertions, 1 deletions

diff --git a/vm/compiler/CompilerIR.h b/vm/compiler/CompilerIR.h
index 21aadec3a..82b97e5ba 100644
--- a/vm/compiler/CompilerIR.h
+++ b/vm/compiler/CompilerIR.h
@@ -152,6 +152,12 @@ typedef struct BasicBlock {
 struct LoopAnalysis;
 struct RegisterPool;
 
+typedef enum AssemblerStatus {
+    kSuccess,
+    kRetryAll,
+    kRetryHalve
+} AssemblerStatus;
+
 typedef struct CompilationUnit {
     int numInsts;
     int numBlocks;
@@ -166,11 +172,12 @@ typedef struct CompilationUnit {
     int headerSize;                     // bytes before the first code ptr
     int dataOffset;                     // starting offset of literal pool
     int totalSize;                      // header + code size
+    AssemblerStatus assemblerStatus;    // Success or fix and retry
+    int assemblerRetries;               // How many times tried to fix assembly
     unsigned char *codeBuffer;
     void *baseAddr;
     bool printMe;
     bool allSingleStep;
-    bool halveInstCount;
     bool executionCount;                // Add code to count trace executions
     bool hasLoop;                       // Contains a loop
     bool hasInvoke;                     // Contains an invoke instruction