https://llvm.org/bugs/show_bug.cgi?id=31164
Bug ID: 31164
Summary: x64 backend creates unnecessary setcc instructions
Product: tools
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: llc
Assignee: unassignedb...@nondot.org
Reporter: e...@arbat.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
An i1 phi is cleverly placed in the processor status word, but then when we
want to branch on it, it is materialized in a setcc-testb-je sequence instead
of just a jne instruction.
Input .ll:
define i64 @foo(i64, i64, i64) {
%4 = icmp eq i64 %0, 0
br i1 %4, label %left, label %right
left:
%l = icmp eq i64 %1, 1
br label %join
right:
%r = icmp eq i64 %1, %2
br label %join
join:
%lr = phi i1 [%l, %left], [%r, %right]
%iszero = icmp eq i1 %lr, 0
br i1 %iszero, label %left2, label %right2
left2:
ret i64 %2
right2:
ret i64 %0
}
Output x64
foo: # @foo
.cfi_startproc
# BB#0:
testq %rdi, %rdi
je .LBB0_1
# BB#2: # %right
cmpq %rdx, %rsi
jmp .LBB0_3
.LBB0_1: # %left
cmpq $1, %rsi
.LBB0_3: # %join
sete %al
testb %al, %al
je .LBB0_4
# BB#5: # %right2
movq %rdi, %rax
retq
.LBB0_4: # %left2
movq %rdx, %rax
retq
See http://pastebin.com/UinMkFr1 and http://pastebin.com/Su1b1mxj for syntax
coloured versions.
The sete and testb instructions are superfluous.
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