Update peephole optimizer
+ Save one instruction for loads of local byte or float values.
+ Save two instructions for pointer arithmetic with a stride that
is a power of two.
diff --git a/libacc/acc.cpp b/libacc/acc.cpp
index 62dea4c..6dccc5b 100644
--- a/libacc/acc.cpp
+++ b/libacc/acc.cpp
@@ -730,6 +730,18 @@
return rotateRight(data, rotate);
}
+ static bool isPowerOfTwo(size_t n) {
+ return (n != 0) & ((n & (n-1)) == 0);
+ }
+
+ static size_t log2(size_t n) {
+ int result = 0;
+ while (n >>= 1) {
+ result++;
+ }
+ return result;
+ }
+
class ARMCodeBuf : public ICodeBuf {
ICodeBuf* mpBase;
ErrorSink* mErrorSink;
@@ -825,8 +837,9 @@
// Peephole check
bool didPeep;
do {
- const unsigned int opMask = 0x01e00000;
- const unsigned int immediateMask = 0x00000fff;
+ static const unsigned int opMask = 0x01e00000;
+ static const unsigned int immediateMask = 0x00000fff;
+ static const unsigned int BMask = 0x00400000;
didPeep = false;
if (mQ.count() >= 4) {
@@ -853,16 +866,25 @@
}
// Load local variable
- // sub r0,r11,#imm;ldr r0,[r0] ==> ldr r0, [r11,#-imm]
+ // sub r0,r11,#imm;ldr/ldrb r0,[r0] ==> ldr/ldrb r0, [r11,#-imm]
if (mQ.count() >= 2) {
- if ((mQ[-2] & ~immediateMask) == 0xe24b0000 && // sub r0,r11,#imm
- mQ[-1] == 0xe5900000) { // ldr r0, [r0]
- unsigned int op = mQ[-2];
- unsigned int ld = mQ[-1];
- unsigned int combined = (op & immediateMask) | 0xE51B0000; // ldr r0, [r11, #-0]
- mQ.popBack(2);
- mQ.pushBack(combined);
- didPeep = true;
+ if ((mQ[-2] & ~immediateMask) == 0xe24b0000) { // sub r0,r11,#imm
+ const unsigned int encodedImmediate = mQ[-2] & immediateMask;
+ const unsigned int ld = mQ[-1];
+ if ((ld & ~BMask) == 0xe5900000) { // ldr{b} r0, [r0]
+ unsigned int combined = encodedImmediate | (0xE51B0000 | (ld & BMask)); // ldr r0, [r11, #-0]
+ mQ.popBack(2);
+ mQ.pushBack(combined);
+ didPeep = true;
+ } else if (ld == 0xedd07a00) { // ldcl p10, c7, [r0, #0x000]
+ unsigned int decodedImmediate = decode12BitImmediate(encodedImmediate);
+ if (decodedImmediate <= 1020 && ((decodedImmediate & 3) == 0)) {
+ unsigned int combined = (decodedImmediate >> 2) | 0xed5b7a00; // ldcl p10, c7, [r11, #-0]
+ mQ.popBack(2);
+ mQ.pushBack(combined);
+ didPeep = true;
+ }
+ }
}
}
@@ -891,6 +913,21 @@
}
}
+ // Pointer arithmetic with a stride that is a power of two
+
+ if (mQ.count() >= 3 &&
+ (mQ[-3] & ~ immediateMask) == 0xe3a02000 && // mov r2, #stride
+ mQ[-2] == 0xe0000092 && // mul r0, r2, r0
+ mQ[-1] == 0xe0810000) { // add r0, r1, r0
+ int stride = decode12BitImmediate(mQ[-3]);
+ if (isPowerOfTwo(stride)) {
+ mQ.popBack(3);
+ unsigned int add = 0xe0810000 | (log2(stride) << 7); // add r0, r1, r0, LSL #log2(stride)
+ mQ.pushBack(add);
+ didPeep = true;
+ }
+ }
+
} while (didPeep);
#endif
}