Add a test case to show isKnownNonZero() returns correctly; NFC

[junbuml]

Summary

Added a test case just to make sure that isKnownNonZero() returns false
when we cannot guarantee that a ConstantExpr is a non-zero constant.

[mssimpso]

Jun,

This makes sense to me. But I'm curious if you've seen any changes with this because it doesn't look to be functionally identical, due to the extra floating point checking done in isZeroValue. While you're here, it would be nice to fix the comment for the function to mention the constants.

[junbuml]

This makes sense to me. But I'm curious if you've seen any changes with this because it doesn't look to be functionally identical, due to the extra floating point checking done in isZeroValue. While you're here, it would be nice to fix the comment for the function to mention the constants.

I am sending this out to get any early feedback. Since this is not a NFC, I need to check performance. This is also missing test cases that I will add soon.

[nlewycky]

What about a ConstantExpr like "and(ptrtoint(@global), 32)"? We don't know the 5th bit of the address of @global, so C->isZeroValue() returns false (since we don't know it's zero), but isKnownNonZero must also return false (since we don't know it's non-zero). With your patch, we would incorrectly return true.

You are replacing "is known to be non-zero" with "is not known to be zero" which are not quite the same thing for all Constants. Please send out a patch which adds a testcase that would fail if someone were to propose this change in the future.

[junbuml]

Based on Nick's comment, I just added a test case to prevent any similar changes in future.
Thanks Nick for the comment.

[mcrosier]

LGTM, with minor nits.

test/Transforms/InstSimplify/compare.ll

336 ↗

(On Diff #47648)

Please drop "expect to".

Also, please maximize 80-column.

[junbuml]

Addressed Chad's comment.

llvm/trunk/test/Transforms/InstSimplify/compare.ll

 define i1 @or(i32 %x) {
 ; CHECK-LABEL: @or(
   %o = or i32 %x, 1
   %c = icmp eq i32 %o, 0
   ret i1 %c
 ; CHECK: ret i1 false
 }
 
+; Do not simplify if we cannot guarantee that the ConstantExpr is a non-zero
+; constant.
+@GV = common global i32* null
+define i1 @or_constexp(i32 %x) {
+; CHECK-LABEL: @or_constexp(
+entry:
+  %0 = and i32 ptrtoint (i32** @GV to i32), 32
+  %o = or i32 %x, %0
+  %c = icmp eq i32 %o, 0
+  ret i1 %c
+; CHECK: or
+; CHECK-NEXT: icmp eq
+; CHECK-NOT: ret i1 false
+}
+
 define i1 @shl1(i32 %x) {
 ; CHECK-LABEL: @shl1(
   %s = shl i32 1, %x
   %c = icmp eq i32 %s, 0
   ret i1 %c
 ; CHECK: ret i1 false
 }