Skip constant folding the loop predicates if the loop contains control
convergence tokens referenced outside the loop.
Fixes https://github.com/llvm/llvm-project/issues/164496.
Verified
[loop_peeling.test](https://github.com/llvm/offload-test-suite/pull/473)
passes with the fix.
Similar control convergence issues are found on other passes.
https://github.com/llvm/llvm-project/issues/165642
HLSL used for tests:
```hlsl
RWStructuredBuffer<uint> Out : register(u0);
[numthreads(8,1,1)]
void main(uint3 TID : SV_GroupThreadID) {
for (uint i = 0; i < 8; i++) {
if (i == TID.x) {
Out[TID.x] = WaveActiveMax(TID.x);
break;
}
}
}
```
With nested loop:
```hlsl
RWStructuredBuffer<uint> Out : register(u0);
[numthreads(8,8,1)]
void main(uint3 TID : SV_GroupThreadID) {
for (uint i = 0; i < 8; i++) {
for (uint j = 0; j < 8; j++) {
if (i == TID.x && j == TID.y) {
uint index = TID.x * 8 + TID.y;
Out[index] = WaveActiveMax(index);
break;
}
}
}
}
```
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