[SLP]Add better minbitwidth analysis for udiv/urem instructions.

[alexey-bataev]

Adds improved bitwidth analysis for udiv/urem instructions. The
analysis is based on similar version in InstCombiner.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Alexey Bataev (alexey-bataev)

Changes

Adds improved bitwidth analysis for udiv/urem instructions. The
analysis is based on similar version in InstCombiner.

---

Full diff: https://github.com/llvm/llvm-project/pull/85928.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp (+22)
• (modified) llvm/test/Transforms/SLPVectorizer/X86/reorder-possible-strided-node.ll (+2-6)

diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index 5d59f35f30810e..f8f7015e5f15f2 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -14165,6 +14165,28 @@ bool BoUpSLP::collectValuesToDemote(
       return false;
     break;
   }
+  case Instruction::UDiv:
+  case Instruction::URem: {
+    if (ITE->UserTreeIndices.size() > 1 && !IsPotentiallyTruncated(I, BitWidth))
+      return false;
+    // UDiv and URem can be truncated if all the truncated bits are zero.
+    if (!AttemptCheckBitwidth(
+            [&](unsigned BitWidth, unsigned OrigBitWidth) {
+              assert(BitWidth <= OrigBitWidth && "Unexpected bitwidths!");
+              APInt Mask = APInt::getBitsSetFrom(OrigBitWidth, BitWidth);
+              return MaskedValueIsZero(I->getOperand(0), Mask,
+                                       SimplifyQuery(*DL)) &&
+                     MaskedValueIsZero(I->getOperand(1), Mask,
+                                       SimplifyQuery(*DL));
+            },
+            NeedToExit))
+      return false;
+    if (NeedToExit)
+      return true;
+    if (!ProcessOperands({I->getOperand(0), I->getOperand(1)}, NeedToExit))
+      return false;
+    break;
+  }
 
   // We can demote selects if we can demote their true and false values.
   case Instruction::Select: {
diff --git a/llvm/test/Transforms/SLPVectorizer/X86/reorder-possible-strided-node.ll b/llvm/test/Transforms/SLPVectorizer/X86/reorder-possible-strided-node.ll
index 4a23abf182e888..cfbbe14186b501 100644
--- a/llvm/test/Transforms/SLPVectorizer/X86/reorder-possible-strided-node.ll
+++ b/llvm/test/Transforms/SLPVectorizer/X86/reorder-possible-strided-node.ll
@@ -116,9 +116,7 @@ define void @test_div() {
 ; CHECK-NEXT:    [[TMP1:%.*]] = load <4 x i32>, ptr [[ARRAYIDX22]], align 4
 ; CHECK-NEXT:    [[TMP2:%.*]] = shufflevector <4 x i32> [[TMP1]], <4 x i32> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
 ; CHECK-NEXT:    [[TMP3:%.*]] = mul <4 x i32> [[TMP2]], [[TMP0]]
-; CHECK-NEXT:    [[TMP4:%.*]] = zext <4 x i32> [[TMP3]] to <4 x i64>
-; CHECK-NEXT:    [[TMP5:%.*]] = udiv <4 x i64> [[TMP4]], <i64 1, i64 2, i64 1, i64 2>
-; CHECK-NEXT:    [[TMP6:%.*]] = trunc <4 x i64> [[TMP5]] to <4 x i32>
+; CHECK-NEXT:    [[TMP6:%.*]] = udiv <4 x i32> [[TMP3]], <i32 1, i32 2, i32 1, i32 2>
 ; CHECK-NEXT:    store <4 x i32> [[TMP6]], ptr getelementptr inbounds ([4 x i32], ptr null, i64 8, i64 0), align 16
 ; CHECK-NEXT:    ret void
 ;
@@ -170,9 +168,7 @@ define void @test_rem() {
 ; CHECK-NEXT:    [[TMP1:%.*]] = load <4 x i32>, ptr [[ARRAYIDX22]], align 4
 ; CHECK-NEXT:    [[TMP2:%.*]] = shufflevector <4 x i32> [[TMP1]], <4 x i32> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
 ; CHECK-NEXT:    [[TMP3:%.*]] = mul <4 x i32> [[TMP2]], [[TMP0]]
-; CHECK-NEXT:    [[TMP4:%.*]] = zext <4 x i32> [[TMP3]] to <4 x i64>
-; CHECK-NEXT:    [[TMP5:%.*]] = urem <4 x i64> [[TMP4]], <i64 1, i64 2, i64 1, i64 1>
-; CHECK-NEXT:    [[TMP6:%.*]] = trunc <4 x i64> [[TMP5]] to <4 x i32>
+; CHECK-NEXT:    [[TMP6:%.*]] = urem <4 x i32> [[TMP3]], <i32 1, i32 2, i32 1, i32 1>
 ; CHECK-NEXT:    store <4 x i32> [[TMP6]], ptr getelementptr inbounds ([4 x i32], ptr null, i64 8, i64 0), align 16
 ; CHECK-NEXT:    ret void
 ;

[RKSimon]

This is starting to have a lot of code similar to canEvaluateTruncated in InstCombineCasts.cpp - can we reuse that code somehow - move it to ValueTracking.h or something?

[alexey-bataev]

Yeah, I thought about this. Actually, only the code for shifts/div/rem is duplicated, all other code is unique and/or requires some extra processing, which canEvaluateTruncated does not have. We can think about it later.

[github-actions]

✅ With the latest revision this PR passed the Python code formatter.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[alexey-bataev]

Ping!

[RKSimon]

LGTM