[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

1 files changed, 141 insertions, 0 deletions

diff --git a/llvm/test/Analysis/ScalarEvolution/shl-lshr-differentconstmask.ll b/llvm/test/Analysis/ScalarEvolution/shl-lshr-differentconstmask.ll
new file mode 100644
index 00000000000..be97990e116
--- /dev/null
+++ b/llvm/test/Analysis/ScalarEvolution/shl-lshr-differentconstmask.ll
@@ -0,0 +1,141 @@
+; 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 @mul_biggerShl(i32 %val) nounwind {
+; CHECK-LABEL: 'mul_biggerShl'
+; CHECK-NEXT:  Classifying expressions for: @mul_biggerShl
+; CHECK-NEXT:    %tmp1 = mul i32 %val, 64
+; CHECK-NEXT:    -->  (64 * %val) U: [0,-63) S: [-2147483648,2147483585)
+; CHECK-NEXT:    %tmp2 = udiv i32 %tmp1, 16
+; CHECK-NEXT:    -->  ((64 * %val) /u 16) U: [0,268435453) S: [0,268435456)
+; CHECK-NEXT:  Determining loop execution counts for: @mul_biggerShl
+;
+  %tmp1 = mul i32 %val, 64
+  %tmp2 = udiv i32 %tmp1, 16
+  ret i32 %tmp2
+}
+
+define i32 @mul_biggerLshl(i32 %val) nounwind {
+; CHECK-LABEL: 'mul_biggerLshl'
+; CHECK-NEXT:  Classifying expressions for: @mul_biggerLshl
+; CHECK-NEXT:    %tmp1 = mul i32 %val, 16
+; CHECK-NEXT:    -->  (16 * %val) U: [0,-15) S: [-2147483648,2147483633)
+; CHECK-NEXT:    %tmp2 = udiv i32 %tmp1, 64
+; CHECK-NEXT:    -->  ((16 * %val) /u 64) U: [0,67108864) S: [0,67108864)
+; CHECK-NEXT:  Determining loop execution counts for: @mul_biggerLshl
+;
+  %tmp1 = mul i32 %val, 16
+  %tmp2 = udiv i32 %tmp1, 64
+  ret i32 %tmp2
+}
+
+; Or, it could have been transformed to shifts
+
+define i32 @shifty_biggerShl(i32 %val) {
+; CHECK-LABEL: 'shifty_biggerShl'
+; CHECK-NEXT:  Classifying expressions for: @shifty_biggerShl
+; CHECK-NEXT:    %tmp1 = shl i32 %val, 6
+; CHECK-NEXT:    -->  (64 * %val) U: [0,-63) S: [-2147483648,2147483585)
+; CHECK-NEXT:    %tmp2 = lshr i32 %tmp1, 4
+; CHECK-NEXT:    -->  ((64 * %val) /u 16) U: [0,268435453) S: [0,268435456)
+; CHECK-NEXT:  Determining loop execution counts for: @shifty_biggerShl
+;
+  %tmp1 = shl i32 %val, 6
+  %tmp2 = lshr i32 %tmp1, 4
+  ret i32 %tmp2
+}
+
+define i32 @shifty_biggerShl_shlnuw(i32 %val) {
+; CHECK-LABEL: 'shifty_biggerShl_shlnuw'
+; CHECK-NEXT:  Classifying expressions for: @shifty_biggerShl_shlnuw
+; CHECK-NEXT:    %tmp1 = shl nuw i32 %val, 6
+; CHECK-NEXT:    -->  (64 * %val) U: [0,-63) S: [-2147483648,2147483585)
+; CHECK-NEXT:    %tmp2 = lshr i32 %tmp1, 4
+; CHECK-NEXT:    -->  ((64 * %val) /u 16) U: [0,268435453) S: [0,268435456)
+; CHECK-NEXT:  Determining loop execution counts for: @shifty_biggerShl_shlnuw
+;
+  %tmp1 = shl nuw i32 %val, 6
+  %tmp2 = lshr i32 %tmp1, 4
+  ret i32 %tmp2
+}
+
+define i32 @shifty_biggerLshr(i32 %val) {
+; CHECK-LABEL: 'shifty_biggerLshr'
+; CHECK-NEXT:  Classifying expressions for: @shifty_biggerLshr
+; CHECK-NEXT:    %tmp1 = shl i32 %val, 4
+; CHECK-NEXT:    -->  (16 * %val) U: [0,-15) S: [-2147483648,2147483633)
+; CHECK-NEXT:    %tmp2 = lshr i32 %tmp1, 6
+; CHECK-NEXT:    -->  ((16 * %val) /u 64) U: [0,67108864) S: [0,67108864)
+; CHECK-NEXT:  Determining loop execution counts for: @shifty_biggerLshr
+;
+  %tmp1 = shl i32 %val, 4
+  %tmp2 = lshr i32 %tmp1, 6
+  ret i32 %tmp2
+}
+
+define i32 @shifty_biggerLshr_shlnuw(i32 %val) {
+; CHECK-LABEL: 'shifty_biggerLshr_shlnuw'
+; CHECK-NEXT:  Classifying expressions for: @shifty_biggerLshr_shlnuw
+; CHECK-NEXT:    %tmp1 = shl nuw i32 %val, 4
+; CHECK-NEXT:    -->  (16 * %val) U: [0,-15) S: [-2147483648,2147483633)
+; CHECK-NEXT:    %tmp2 = lshr i32 %tmp1, 6
+; CHECK-NEXT:    -->  ((16 * %val) /u 64) U: [0,67108864) S: [0,67108864)
+; CHECK-NEXT:  Determining loop execution counts for: @shifty_biggerLshr_shlnuw
+;
+  %tmp1 = shl nuw i32 %val, 4
+  %tmp2 = lshr i32 %tmp1, 6
+  ret i32 %tmp2
+}
+
+; Or, further folded into mask variant.
+
+define i32 @masky_biggerShl(i32 %val) {
+; CHECK-LABEL: 'masky_biggerShl'
+; CHECK-NEXT:  Classifying expressions for: @masky_biggerShl
+; CHECK-NEXT:    %tmp1 = shl i32 %val, 2
+; CHECK-NEXT:    -->  (4 * %val) U: [0,-3) S: [-2147483648,2147483645)
+; CHECK-NEXT:    %tmp2 = and i32 %tmp1, 268435452
+; CHECK-NEXT:    -->  (4 * (zext i26 (trunc i32 %val to i26) to i32)) U: [0,268435453) S: [0,268435453)
+; CHECK-NEXT:  Determining loop execution counts for: @masky_biggerShl
+;
+  %tmp1 = shl i32 %val, 2
+  %tmp2 = and i32 %tmp1, 268435452
+  ret i32 %tmp2
+}
+
+define i32 @masky_biggerShl_shlnuw(i32 %val) {
+; CHECK-LABEL: 'masky_biggerShl_shlnuw'
+; CHECK-NEXT:  Classifying expressions for: @masky_biggerShl_shlnuw
+; CHECK-NEXT:    %tmp1 = shl nuw i32 %val, 2
+; CHECK-NEXT:    -->  (4 * %val) U: [0,-3) S: [-2147483648,2147483645)
+; CHECK-NEXT:  Determining loop execution counts for: @masky_biggerShl_shlnuw
+;
+  %tmp1 = shl nuw i32 %val, 2
+  ret i32 %tmp1
+}
+
+define i32 @masky_biggerLshr(i32 %val) {
+; CHECK-LABEL: 'masky_biggerLshr'
+; CHECK-NEXT:  Classifying expressions for: @masky_biggerLshr
+; CHECK-NEXT:    %tmp1 = lshr i32 %val, 2
+; CHECK-NEXT:    -->  (%val /u 4) U: [0,1073741824) S: [0,1073741824)
+; CHECK-NEXT:    %tmp2 = and i32 %tmp1, 67108863
+; CHECK-NEXT:    -->  (zext i26 (trunc i32 (%val /u 4) to i26) to i32) U: [0,67108864) S: [0,67108864)
+; CHECK-NEXT:  Determining loop execution counts for: @masky_biggerLshr
+;
+  %tmp1 = lshr i32 %val, 2
+  %tmp2 = and i32 %tmp1, 67108863
+  ret i32 %tmp2
+}
+
+define i32 @masky_biggerLshr_shlnuw(i32 %val) {
+; CHECK-LABEL: 'masky_biggerLshr_shlnuw'
+; CHECK-NEXT:  Classifying expressions for: @masky_biggerLshr_shlnuw
+; CHECK-NEXT:    %tmp1 = lshr i32 %val, 2
+; CHECK-NEXT:    -->  (%val /u 4) U: [0,1073741824) S: [0,1073741824)
+; CHECK-NEXT:  Determining loop execution counts for: @masky_biggerLshr_shlnuw
+;
+  %tmp1 = lshr i32 %val, 2
+  ret i32 %tmp1
+}