Souper says:
; Function: fn2
%0:i32 = var
%1:i32 = lshr 1:i32, %0
%2:i1 = slt 4294967295:i32, %1
cand %2 1:i1
COMMAND: /home/regehr/souper/build/souper -stp-path=/usr/local/bin/stp reduce_685/foo.bc
LLVM says:
define i32 @fn1(i32 %p1) #0 {
entry:
%cmp = icmp sgt i32 %p1, -1
%p1.lobit = lshr i32 %p1, 31
%p1.lobit.not = xor i32 %p1.lobit, 1
%conv. = select i1 %cmp, i32 %p1.lobit.not, i32 0
ret i32 %conv.
}
define void @fn2() #1 {
entry:
%0 = load i32* @a, align 4, !tbaa !1
%shr = lshr i32 1, %0
store i32 %shr, i32* @d, align 4, !tbaa !1
store i32 %shr, i32* @c, align 4, !tbaa !1
%cmp.i = icmp sgt i32 %shr, -1
%p1.lobit.i = lshr i32 %shr, 31
%p1.lobit.not.i = xor i32 %p1.lobit.i, 1
%conv..i = select i1 %cmp.i, i32 %p1.lobit.not.i, i32 0
store i32 %conv..i, i32* @b, align 4, !tbaa !1
ret void
}
COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -c -w -emit-llvm -O3 reduce_685/foo.c -o reduce_685/foo.bc
C source code:
int a, b, c, d;
int fn1(p1) { return p1 >= 0 ?: 0; }
void fn2() {
int *e = &c;
d = 1 >> a;
c = d;
b = fn1(*e);
}
x86-64 from LLVM:
fn1: # @fn1
movl %edi, %ecx
shrl $31, %ecx
xorl $1, %ecx
xorl %eax, %eax
testl %edi, %edi
cmovnsl %ecx, %eax
retq
fn2: # @fn2
movb a(%rip), %cl
movl $1, %eax
shrl %cl, %eax
movl %eax, %ecx
shrl $31, %ecx
xorl $1, %ecx
xorl %edx, %edx
testl %eax, %eax
movl %eax, d(%rip)
movl %eax, c(%rip)
cmovnsl %ecx, %edx
movl %edx, b(%rip)
retq
.Ltmp1:
COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -w -O3 reduce_685/foo.c -S -o -
x86-64 from GCC:
fn1:
movl %edi, %eax
notl %eax
shrl $31, %eax
ret
fn2:
.LFB1:
movl a(%rip), %ecx
movl $1, %eax
sarl %cl, %eax
movl %eax, d(%rip)
movl %eax, c(%rip)
notl %eax
shrl $31, %eax
movl %eax, b(%rip)
ret
.LFE1:
COMMAND: gcc -w -O3 reduce_685/foo.c -S -o -