Hi,
The following code snippet:
static int test_do(void) {
int a = 0;
int count = 27;
switch (count % 8) {
case 0: do { a++;
case 7: a++;
case 6: a++;
case 5: a++;
case 4: a++;
case 3: a++;
case 2: a++;
case 1: a++;
} while ((count -= 8) > 0);
}
return a;
}
Results in following linear output:
test_do:
.L0:
<entry-point>
phisrc.32 %phi3(a) <- $0
phisrc.32 %phi4(a) <- $0
phisrc.32 %phi6(a) <- $0
phisrc.32 %phi8(a) <- $0
phisrc.32 %phi10(a) <- $0
phisrc.32 %phi12(a) <- $0
phisrc.32 %phi14(a) <- $0
phisrc.32 %phi16(a) <- $0
phisrc.32 %phi18(a) <- $0
phisrc.32 %phi20(count) <- $27
br .L7
.L10:
phi.32 %r3 <- %phi18(a), %phi19(a)
add.32 %r4 <- %r3, $1
phisrc.32 %phi17(a) <- %r4
phi.32 %r5 <- %phi16(a), %phi17(a)
add.32 %r6 <- %r5, $1
phisrc.32 %phi15(a) <- %r6
phi.32 %r7 <- %phi14(a), %phi15(a)
add.32 %r8 <- %r7, $1
phisrc.32 %phi13(a) <- %r8
phi.32 %r9 <- %phi12(a), %phi13(a)
add.32 %r10 <- %r9, $1
phisrc.32 %phi11(a) <- %r10
phi.32 %r11 <- %phi10(a), %phi11(a)
add.32 %r12 <- %r11, $1
phisrc.32 %phi9(a) <- %r12
br .L7
.L7:
phi.32 %r13 <- %phi8(a), %phi9(a)
add.32 %r14 <- %r13, $1
phisrc.32 %phi7(a) <- %r14
phi.32 %r15 <- %phi6(a), %phi7(a)
add.32 %r16 <- %r15, $1
phisrc.32 %phi5(a) <- %r16
phi.32 %r17 <- %phi4(a), %phi5(a)
add.32 %r18(a) <- %r17, $1
phisrc.32 %phi2(a) <- %r18(a)
phisrc.32 %phi19(a) <- %r18(a)
phi.32 %r19 <- %phi20(count), %phi21(count)
add.32 %r21 <- %r19, $-8
setgt.32 %r23 <- %r21, $0
phisrc.32 %phi21(count) <- %r21
cbr %r23, .L10, .L1
.L1:
phi.32 %r24 <- %phi2(a), %phi3(a)
ret.32 %r24
This is translated to following LLVM IR:
define internal i32 @test_do() {
L0:
%0 = alloca i32
%1 = alloca i32
%2 = alloca i32
%3 = alloca i32
%4 = alloca i32
%5 = alloca i32
%6 = alloca i32
%7 = alloca i32
%8 = alloca i32
%9 = alloca i32
store i32 0, i32* %9
store i32 0, i32* %7
store i32 0, i32* %6
store i32 0, i32* %5
store i32 0, i32* %4
store i32 0, i32* %3
store i32 0, i32* %2
store i32 0, i32* %1
store i32 0, i32* %0
store i32 27, i32* %8
br label %L2
L1: ; preds = %L2
%10 = load i32, i32* %0
%R4 = add i32 %10, 1
store i32 %R4, i32* %1
%11 = load i32, i32* %1
%R6 = add i32 %11, 1
store i32 %R6, i32* %2
%12 = load i32, i32* %2
%R8 = add i32 %12, 1
store i32 %R8, i32* %3
%13 = load i32, i32* %3
%R10 = add i32 %13, 1
store i32 %R10, i32* %4
%14 = load i32, i32* %4
%R12 = add i32 %14, 1
store i32 %R12, i32* %5
br label %L2
L2: ; preds = %L1, %L0
%15 = load i32, i32* %5
%R14 = add i32 %15, 1
store i32 %R14, i32* %6
%16 = load i32, i32* %6
%R16 = add i32 %16, 1
store i32 %R16, i32* %7
%17 = load i32, i32* %7
%R18 = add i32 %17, 1
store i32 %R18, i32* %9
store i32 %R18, i32* %0
%18 = load i32, i32* %8
%R21 = add i32 %18, -8
%R23 = icmp sgt i32 %R21, 0
%R231 = zext i1 %R23 to i32
store i32 %R21, i32* %8
%cond = icmp ne i32 %R231, 0
br i1 %cond, label %L1, label %L3
L3: ; preds = %L2
%19 = load i32, i32* %9
ret i32 %19
}
It seems to me that 'a' ends up having 9 different slots on the stack,
but it should really be merged into one slot, i.e. we should detect
that the phis all related to the same symbol, and create only one
alloca?
Regards
Dibyendu
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