48 lines
1.1 KiB
C
48 lines
1.1 KiB
C
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#include "test.h"
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/*
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* https://github.com/davidgiven/ack/issues/203 was a bug in the
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* strength reduction (SR) phase of ego. To cause the bug:
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*
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* 1. SR must run; it runs at `ack -O3` and higher.
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*
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* 2. SR must find a loop with an induction variable, and SR must
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* find at least 2 different expressions using the variable, like
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* i << 1, (i + 1) << 1, or 3 * i, 5 * i.
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*
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* 3. There is no basic block to act as a loop header, so SR must
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* create the block. One way is to put if (one) { ... } around
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* the loop, so the loop is just after a conditional branch.
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*/
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/*
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* Global variables prevent optimizations:
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* if (one) { ... } caused the bug, if (1) { ... } didn't.
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*/
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int zero = 0;
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int one = 1;
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short ary[] = {8, 8, 8, 8, 8, 9};
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int left_shift(int i) {
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if (one) {
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/* EM will use i << 1, (i + 1) << 1 here. */
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while (ary[i] == ary[i + 1])
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i++;
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}
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return i;
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}
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int multiply(int i) {
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if (one) {
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while (((3 * i) & (5 * i)) < 40)
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i++;
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}
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return i;
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}
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int main(void) {
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ASSERT(left_shift(zero) == 4);
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ASSERT(multiply(zero) == 21);
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finished();
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}
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