https://llvm.org/bugs/show_bug.cgi?id=23202
Bug ID: 23202
Summary: Registers are moved around in do{}while(); loop
Product: libraries
Version: 3.5
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Created attachment 14189
--> https://llvm.org/bugs/attachment.cgi?id=14189&action=edit
The whole function
The loop:
do{
previous = next;
in_pos++;
*out_pos++ = previous;
if(in_pos == in_limit)
goto end;
next = *in_pos;
}while(previous != next);
is translateted with -O2 to:
.LBB0_3: # Parent Loop BB0_2 Depth=1
# => This Inner Loop Header: Depth=2
#DEBUG_VALUE: xrle_compress:out <- R14
#DEBUG_VALUE: xrle_compress:repeat <- 1
mov rax, rdi
mov rcx, rsi
mov r13, rdx
add r13, 16
mov qword ptr [rbx], rax
cmp r12, rcx
je .LBB0_4
# BB#7: # in Loop: Header=BB0_3 Depth=2
#DEBUG_VALUE: xrle_compress:out <- R14
#DEBUG_VALUE: xrle_compress:repeat <- 1
mov rdi, qword ptr [rcx]
#DEBUG_VALUE: xrle_compress:next <- RDI
lea rsi, qword ptr [rcx + 8]
cmp rax, rdi
mov rdx, rbx
mov rbx, r13
jne .LBB0_3
Notice how many mov instructions are used:
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