[NFC][SCEV] Add tests related to bit masking (PR37793)
Summary:
Related to https://bugs.llvm.org/show_bug.cgi?id=37793, https://reviews.llvm.org/D46760#1127287
We'd like to do this canonicalization https://rise4fun.com/Alive/Gmc
But it is currently restricted by rL155136 / rL155362, which says:
```
// This is a constant shift of a constant shift. Be careful about hiding
// shl instructions behind bit masks. They are used to represent multiplies
// by a constant, and it is important that simple arithmetic expressions
// are still recognizable by scalar evolution.
//
// The transforms applied to shl are very similar to the transforms applied
// to mul by constant. We can be more aggressive about optimizing right
// shifts.
//
// Combinations of right and left shifts will still be optimized in
// DAGCombine where scalar evolution no longer applies.
```
I think these tests show that for *constants*, SCEV has no issues with that canonicalization.
Reviewers: mkazantsev, spatel, efriedma, sanjoy
Reviewed By: mkazantsev
Subscribers: sanjoy, javed.absar, llvm-commits, stoklund, bixia
Differential Revision: https://reviews.llvm.org/D48229
llvm-svn: 335101
diff --git a/llvm/test/Analysis/ScalarEvolution/extract-highbits-sameconstmask.ll b/llvm/test/Analysis/ScalarEvolution/extract-highbits-sameconstmask.ll
new file mode 100644
index 0000000..851dce6
--- /dev/null
+++ b/llvm/test/Analysis/ScalarEvolution/extract-highbits-sameconstmask.ll
@@ -0,0 +1,60 @@
+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
+; RUN: opt -S -analyze -scalar-evolution < %s | FileCheck %s
+
+; The obvious case.
+define i32 @div(i32 %val) nounwind {
+; CHECK-LABEL: 'div'
+; CHECK-NEXT: Classifying expressions for: @div
+; CHECK-NEXT: %tmp1 = udiv i32 %val, 16
+; CHECK-NEXT: --> (%val /u 16) U: [0,268435456) S: [0,268435456)
+; CHECK-NEXT: %tmp2 = mul i32 %tmp1, 16
+; CHECK-NEXT: --> (16 * (%val /u 16)) U: [0,-15) S: [0,-15)
+; CHECK-NEXT: Determining loop execution counts for: @div
+;
+ %tmp1 = udiv i32 %val, 16
+ %tmp2 = mul i32 %tmp1, 16
+ ret i32 %tmp2
+}
+
+define i32 @sdiv(i32 %val) nounwind {
+; CHECK-LABEL: 'sdiv'
+; CHECK-NEXT: Classifying expressions for: @sdiv
+; CHECK-NEXT: %tmp1 = sdiv i32 %val, 16
+; CHECK-NEXT: --> %tmp1 U: full-set S: [-134217728,134217728)
+; CHECK-NEXT: %tmp2 = mul i32 %tmp1, 16
+; CHECK-NEXT: --> (16 * %tmp1) U: [0,-15) S: [-2147483648,2147483633)
+; CHECK-NEXT: Determining loop execution counts for: @sdiv
+;
+ %tmp1 = sdiv i32 %val, 16
+ %tmp2 = mul i32 %tmp1, 16
+ ret i32 %tmp2
+}
+
+; Or, it could be a number of equivalent patterns with mask:
+; b) x & (-1 << nbits)
+; d) x >> nbits << nbits
+
+define i32 @mask_b(i32 %val) nounwind {
+; CHECK-LABEL: 'mask_b'
+; CHECK-NEXT: Classifying expressions for: @mask_b
+; CHECK-NEXT: %masked = and i32 %val, -16
+; CHECK-NEXT: --> (16 * (%val /u 16)) U: [0,-15) S: [0,-15)
+; CHECK-NEXT: Determining loop execution counts for: @mask_b
+;
+ %masked = and i32 %val, -16
+ ret i32 %masked
+}
+
+define i32 @mask_d(i32 %val) nounwind {
+; CHECK-LABEL: 'mask_d'
+; CHECK-NEXT: Classifying expressions for: @mask_d
+; CHECK-NEXT: %lowbitscleared = lshr i32 %val, 4
+; CHECK-NEXT: --> (%val /u 16) U: [0,268435456) S: [0,268435456)
+; CHECK-NEXT: %masked = shl i32 %lowbitscleared, 4
+; CHECK-NEXT: --> (16 * (%val /u 16)) U: [0,-15) S: [0,-15)
+; CHECK-NEXT: Determining loop execution counts for: @mask_d
+;
+ %lowbitscleared = lshr i32 %val, 4
+ %masked = shl i32 %lowbitscleared, 4
+ ret i32 %masked
+}