[llvm-dev] Can't get an induction variable by getInductionVariable API

[ZIN MOON via llvm-dev]

Dear All

I have a question about the getInductionVariable API.
I was trying to get an induction variable (indvar) in the code below using
the getInductionVariable API (LoopInfo class).

*C file*
void test(int val) {
  int sum = 0, i = 0;
  for (i = 0; i < val; i++) {
      sum += i;
  }
}

*IR (with mem2reg pass)*
; Function Attrs: nounwind
define dso_local void @test(i32 %0) #0 {
  br label %2
2:                                                ; preds = %6, %1
  %.01 = phi i32 [ 0, %1 ], [ %5, %6 ]
  %.0 = phi i32 [ 0, %1 ], [ %7, %6 ]
  %3 = icmp slt i32 %.0, %0
  br i1 %3, label %4, label %8 <- *Why don't check this BranchInst ?*
4:                                                ; preds = %2
  %5 = add nsw i32 %.01, %.0
  br label %6
6:                                                ; preds = %4
  %7 = add nsw i32 %.0, 1
 * br label %2  <- checked it whether isCondition by getLatchCmpInst
API(called by getInductionVariable API)*
8:                                                ; preds = %2
  ret void
}

Then I got null (no indvar) because BranchInst's number of operands was
less than 2.(red block).

A CmpInst(compare with induction variable) is contained in the header of
the loop.
But the getInductionVariable API checks only in a latch block(contains a
branch back to the header of the loop)
is there a missing case that contains CmpInst in the header?

And if I use the getCanonicalInductionVariable API, I can get the variable
'i'(%. 01) as an indvar.

I checked the code implementing getInductionVariable and
getCanonicalInductionVariable.
It seems that indvar and canonical indvar differ only in the starting
number (0 or none).
Why not use the same way to detect the indvar between getInductionVariable
and getCanonicalInductionVariable.

BR
ZIN
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