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https://github.com/c64scene-ar/llvm-6502.git
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2c33915628
int tries = INT_MAX;
while (tries > 0) {
tries--;
}
The check should be:
subs r4, #1
cmp r4, #0
bgt LBB0_1
The subs can set the overflow V bit when r4 is INT_MAX+1 (which loop
canonicalization apparently does in this case). cmp #0 would have cleared
it while not changing the N and Z bits. Since BGT is dependent on the V
bit, i.e. (N == V) && !Z, it is not safe to eliminate the cmp #0.
rdar://9172742
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128179 91177308-0d34-0410-b5e6-96231b3b80d8
42 lines
1.1 KiB
LLVM
42 lines
1.1 KiB
LLVM
; RUN: llc < %s -mtriple=thumbv7-apple-darwin10 -relocation-model=pic -disable-fp-elim -mcpu=cortex-a8 | FileCheck %s
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; subs r4, #1
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; cmp r4, 0
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; bgt
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; cmp cannot be optimized away since it will clear the overflow bit.
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; gt / ge, lt, le conditions all depend on V bit.
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; rdar://9172742
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define i32 @t() nounwind {
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; CHECK: t:
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entry:
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br label %bb2
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bb: ; preds = %bb2
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%0 = tail call i32 @rand() nounwind
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%1 = icmp eq i32 %0, 50
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br i1 %1, label %bb3, label %bb1
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bb1: ; preds = %bb
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%tmp = tail call i32 @puts() nounwind
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%indvar.next = add i32 %indvar, 1
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br label %bb2
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bb2: ; preds = %bb1, %entry
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; CHECK: bb2
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; CHECK: subs [[REG:r[0-9]+]], #1
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; CHECK: cmp [[REG]], #0
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; CHECK: bgt
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%indvar = phi i32 [ %indvar.next, %bb1 ], [ 0, %entry ]
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%tries.0 = sub i32 2147483647, %indvar
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%tmp1 = icmp sgt i32 %tries.0, 0
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br i1 %tmp1, label %bb, label %bb3
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bb3: ; preds = %bb2, %bb
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ret i32 0
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}
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declare i32 @rand()
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declare i32 @puts() nounwind
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