Souper says:
; Function: fn1
%0:i8 = var
%1:i1 = slt 255:i8, %0
pc %1 1:i1
%2:i8 = sub 0:i8, %0
%3:i1 = slt 0:i8, %2
cand %3 0:i1
COMMAND: /home/regehr/souper/build/souper -stp-path=/usr/local/bin/stp reduce_378/foo.bc
LLVM says:
define void @fn1() #0 {
entry:
%.pr = load i8* @a, align 1, !tbaa !1
%cmp2 = icmp sgt i8 %.pr, -1
br i1 %cmp2, label %for.body.lr.ph, label %for.end
for.body.lr.ph: ; preds = %entry
%0 = sub i8 0, %.pr
%1 = icmp sgt i8 %0, 0
%.op = add i8 %.pr, -1
%2 = select i1 %1, i8 %.op, i8 -1
store i32 0, i32* @b, align 4, !tbaa !4
store i8 %2, i8* @a, align 1, !tbaa !1
br label %for.end
for.end: ; preds = %for.body.lr.ph, %entry
ret void
}
COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -c -w -emit-llvm -O3 reduce_378/foo.c -o reduce_378/foo.bc
C source code:
char a;
int b;
void fn1() {
for (; a >= 0; a--)
b = 0;
}
x86-64 from LLVM:
fn1: # @fn1
movb a(%rip), %al
testb %al, %al
js .LBB0_5
movb %al, %cl
negb %cl
testb %cl, %cl
jg .LBB0_2
movb $-1, %al
jmp .LBB0_4
.LBB0_2:
decb %al
.LBB0_4: # %for.body.lr.ph
movl $0, b(%rip)
movb %al, a(%rip)
.LBB0_5: # %for.end
retq
COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -w -O3 reduce_378/foo.c -S -o -
x86-64 from GCC:
fn1:
movzbl a(%rip), %eax
testb %al, %al
js .L1
.L6:
subb $1, %al
jns .L6
movl $0, b(%rip)
movb %al, a(%rip)
.L1:
rep ret
COMMAND: gcc -w -O3 reduce_378/foo.c -S -o -