GNU ToolchainCompiler performance

Team

Christophe

Kugan Venkat

Yvan Zhenqiang

Achieved since LCA13

● Switched to gcc-4.8– Lots of backports from trunk

● Gcc-4.7 is now in maintenance● Improved epilogues of leaf functions (can now use LR)● Shrink-wrapping● Progress on conditional compare support● Progress on VRP (Value Range Propagation)● Progress on divmod optimisation● Progress on disabling loop peeling● Address sanitizer

● Shrink-wrapping: move prologue/epilogue inside function body

● Conditional compare support: short-circuit &&/|| if possible:

● VRP: helps removing useless sign/zero extensions

● Divmod: ARM runtime lib contains a routine computing div & mod at the same time

X = a / b; // call div()Y = a % b; // call mod()

(x,y) = divmod(a,b)

short foo(unsigned char c) { c = c & (unsigned char)0x0F ;

if (c > 7) { return c - 6; } return c;}

foo: and r0, r0, #15 cmp r0, #7 subhi r0, r0, #6 uxthhi r0, r0 sxth r0, r0 bx lr

foo: and r0, r0, #15 cmp r0, #7 subhi r0, r0, #6 bx lr

Void test (int a){ If (a == 0) return; ….}

Push {….}If (a == 0) goto Lx;…..Lx:Pop {…}return

If (a == 0) return;Push {…}….Pop {…}Return

If (a == b && c == d) Cmp a,bCmpeq c,d

● Loop peeling: generate out of loop iterations to make sure the loop body makes aligned memory accesses for vectorization. – Mostly useless on ARM which supports unaligned

memory accesses.

● Address sanitizer: new GCC framework to identify NULL pointers accesses, invalid memory references....

Next iteration

● Spec2k analysis– Comparison with x86– Looking for hot spots– Identify and prioritise actions

● Shrink wrapping improvements● Conditional compares● Finalize loop peeling improvements● Neon intrinsics improvements● GCC trunk backports● Compiler target hooks audit